10 Setting Up WebLogic Clusters

Learn the guidelines and instructions for configuring an Oracle WebLogic Server cluster.

This chapter includes the following sections:

• Before You Start
  Learn the prerequisite tasks for setting up a WebLogic Server cluster.
• Cluster Implementation Procedures
  The following sections describe how to get a clustered application up and running from the installation of the WebLogic Server through the initial deployment of application components.

Before You Start

Learn the prerequisite tasks for setting up a WebLogic Server cluster.

• Understand the Configuration Process
  
• Determine Your Cluster Architecture
  
• Consider Your Network and Security Topologies
  
• Choose Machines for the Cluster Installation
  
• Identify Names and Addresses
  

Understand the Configuration Process

If you have a basic understanding of the cluster configuration process and how to accomplish the configuration tasks, information in this section will be most useful.

For information about the configuration facilities available in WebLogic Server and the tasks they support, see Understanding Cluster Configuration.

Determine Your Cluster Architecture

Determine the best cluster architecture that suits your needs. Key architectural decisions include:

• Should you combine all application tiers in a single cluster or segment your application tiers in separate clusters?

• How will you balance the load among server instances in your cluster? Will you:

  • Use basic WebLogic Server load balancing,

  • Implement a third-party load balancer, or

  • Deploy the Web tier of your application on one or more secondary HTTP servers, and proxy requests to it?

• Should you define your Web applications DMZ with one or more firewalls?

To guide these decisions, see Cluster Architectures, and Load Balancing in a Cluster.

The architecture you choose affects how you set up your cluster. The cluster architecture may also require that you install or configure other resources, such as load balancers, HTTP servers, and proxy plug-ins.

Consider Your Network and Security Topologies

Your security requirements form the basis for designing the appropriate security topology. For a discussion of several alternative architectures that provide varying levels of application security, see Security Options for Cluster Architectures.

Note:

Some network topologies can interfere with multicast communication. If you are deploying a cluster across a WAN, see If Your Cluster Spans Multiple Subnets In a WAN .

Avoid deploying server instances in a cluster across a firewall. For a discussion of the impact of tunneling multicast traffic through a firewall, see Firewalls Can Break Multicast Communication.

Choose Machines for the Cluster Installation

Identify the machine or machines where you plan to install WebLogic Server (throughout this section we refer to such machines as "hosts") and ensure that they have the resources required. WebLogic Server allows you to set up a cluster on a single, non-multihomed machine. This new capability is useful for demonstration or development environments.

Note:

Do not install WebLogic Server on machines that have dynamically assigned IP addresses.

• WebLogic Server Instances on Multi-CPU Machines
  
• Check Host Machines' Socket Reader Implementation
  
• Setting Up a Cluster on a Disconnected Windows Machine
  

WebLogic Server Instances on Multi-CPU Machines

WebLogic Server has no built-in limit for the number of server instances that can reside in a cluster. Large, multi-processor servers such as Sun Microsystems, Inc. Sun Enterprise 10000 can host very large clusters or multiple clusters.

Oracle recommends that you start with one server per CPU and then scale up based on the expected behavior. However, as with all capacity planning, you should test the actual deployment with your target Web applications to determine the optimal number and distribution of server instances. For more information see Running Multiple Server Instances on Multi-Core Machines in Tuning Performance of Oracle WebLogic Server for additional information.

Check Host Machines' Socket Reader Implementation

For best socket performance, configure the host to use the native socket reader implementation for your operating system, rather than the pure-Java implementation. For understanding and the instructions about configuring native sockets or optimizing pure-Java socket communications, see Peer-to-Peer Communication Using IP Sockets.

Setting Up a Cluster on a Disconnected Windows Machine

If you want to demonstrate a WebLogic Server cluster on a single, disconnected Windows machine, you must force Windows to load the TCP/IP stack. By default, Windows does not load the TCP/IP stack if it does not detect a physical network connection.

To force Windows to load the TCP/IP stack, disable the Windows media sensing feature using the instructions in How to Disable Media Sense for TCP/IP in Windows.

Identify Names and Addresses

During the cluster configuration process, you supply addressing information, such as IP addresses or DNS names and port numbers for the server instances in the cluster.

For information on intra-cluster communication, and how it enables load balancing and failover, see Choosing WebLogic Server Cluster Messaging Protocols.

When you set up your cluster, you must provide location information for:

• Administration Server

• Managed Servers

• Multicast location

Read the sections that follow for an explanation of the information you must provide, and factors that influence the method you use to identify resources.

• Avoiding Listen Address Problems
  
• Assigning Names to WebLogic Server Resources
  
• Administration Server Address and Port
  
• Managed Server Addresses and Listen Ports
  
• Cluster Multicast Address and Port
  
• Cluster Address
  

Avoiding Listen Address Problems

As you configure a cluster, you can specify address information using either IP addresses or DNS names.

• DNS Names or IP Addresses?
  
• When Internal and External DNS Names Vary
  
• Localhost Considerations
  

DNS Names or IP Addresses?

Consider the purpose of the cluster when deciding whether to use DNS names or IP addresses. For production environments, the use of DNS names is generally recommended. The use of IP addresses can result in translation errors, if:

• Clients will connect to the cluster through a firewall, or

• You have a firewall between the presentation and object tiers. For example, you have a servlet cluster and EJB cluster with a firewall in between, as described in the recommended multitier cluster.

You can avoid translation errors by binding the address of an individual server instance to a DNS name. Make sure that a server instance's DNS name is identical on each side of firewalls in your environment, and do not use a DNS name that is also the name of an NT system on your network.

For more information about using DNS names instead of IP addresses, see Firewall Considerations.

When Internal and External DNS Names Vary

If the internal and external DNS names of a WebLogic Server instance are not identical, use the ExternalDNSName attribute for the server instance to define the server's external DNS name. Outside the firewall the ExternalDNSName should translate to external IP address of the server. If clients are accessing WebLogic Server over the default channel and t3, do not set the ExternalDNSName attribute, even if the internal and external DNS names of a WebLogic Server instance are not identical.

Localhost Considerations

If you identify a server instance's listen address as localhost, non-local processes will not be able to connect to the server instance. Only processes on the machine that hosts the server instance will be able to connect to the server instance. If the server instance must be accessible as localhost (for instance, if you have administrative scripts that connect to localhost), and must also be accessible by remote processes, leave the listen address blank. The server instance will determine the address of the machine and listen on it.

Assigning Names to WebLogic Server Resources

Ensure that each configurable resource in your WebLogic Server environment has a unique name. Each domain, server, machine, cluster, data source, virtual host, or other resource must have a unique name.

Administration Server Address and Port

Identify the DNS name or IP address and listen port of the Administration Server you will use for the cluster.

The Administration Server is the WebLogic Server instance used to configure and manage all the Managed Servers in its domain. When you start a Managed Server, you identify the host and port of its Administration Server.

Managed Server Addresses and Listen Ports

Identify the DNS name or IP address of each Managed Server planned for your cluster.

Each Managed Server in a cluster must have a unique combination of address and listen port number. Clustered server instances on a single non-multihomed machine can have the same address, but must use a different listen port.

Cluster Multicast Address and Port

Identify the address and port you will dedicate to multicast communications for your cluster. A multicast address is an IP address between 224.0.0.0 and 239.255.255.255.

Note:

The default multicast value used by WebLogic Server is 239.192.0.0. You should not use any multicast address with the value x.0.0.1.

Server instances in a cluster communicate with each other using multicast—they use multicast to announce their services, and to issue periodic heartbeats that indicate continued availability.

The multicast address for a cluster should not be used for any purpose other than cluster communications. If the machine where the cluster multicast address exists hosts or is accessed by cluster-external programs that use multicast communication, ensure that those multicast communications use a different port than the cluster multicast port. For more information, see Using IP Multicast.

• Multicast and Multiple Clusters
  
• Multicast and Multitier Clusters
  

Multicast and Multiple Clusters

Multiple clusters on a network may share a multicast address and multicast port combination if necessary.

Multicast and Multitier Clusters

If you are setting up the recommended multitier architecture, described in Cluster Architectures, with a firewall between the clusters, you will need two dedicated multicast addresses: one for the presentation (servlet) cluster and one for the object cluster. Using two multicast addresses ensures that the firewall does not interfere with cluster communication.

Cluster Address

In WebLogic Server cluster, the cluster address is used in entity and stateless beans to construct the host name portion of request URLs.

You can explicitly define the cluster address when you configure a cluster; otherwise, WebLogic Server dynamically generates the cluster address for each new request. For system administration, it is simple to allow the WebLogic Server to generate the cluster address dynamically and is suitable for both development and production environments.

• Dynamic Cluster Address
  
• Explicitly Defining Cluster Address for Production Environments
  
• Explicitly Defining Cluster Address for Development and Test Environments
  
• Explicitly Defining Cluster Address for Single, Multihomed Machine
  

Dynamic Cluster Address

If you do not explicitly define a cluster address when you configure a cluster, and when a clustered server instance receives a remote request, WebLogic Server generates the cluster address, in the form:

listenaddress1:listenport1,listenaddress2:listenport2;listenaddress3:
listenport3 

Each listen address:listen port combination in the cluster address corresponds to Managed Server and network channel that received the request.

• If the request was received on the Managed Server's default channel, the listen address:listen port combinations in the cluster address reflect the ListenAddress and ListenPort values from the associated ServerMBean and SSLMBean instances. See The Default Network Channel in Administering Server Environments for Oracle WebLogic Server.

• If the request was received on a custom network channel, the listen address:listen port in the cluster address reflect the ListenAddress and ListenPort values from NetworkAccessPointMBean that defines the channel. For more information about network channels in a cluster, see Configuring Network Channels For a Cluster in Administering Server Environments for Oracle WebLogic Server.

The number of ListenAddress:ListenPort combinations included in the cluster address is governed by the value of the NumberOfServersInClusterAddress attribute on the ClusterMBean, which is 3 by default.

Note:

You can set NumberOfServersInClusterAddress attribute to a minimum value of 1. This attribute is used when WebLogic Server dynamically constructs cluster address for use with EJBs. In WebLogic Server cluster, the cluster address is used in entity and stateless beans to construct the host name portion of requested URLs. You can explicitly define the cluster address while configuring a cluster. Otherwise, WebLogic Server dynamically generates the cluster address for each new request. Allowing WebLogic Server to dynamically generate the cluster address is the simplest and convenient method for System Administration, and both development and production environments.

You can modify the value of NumberOfServersInClusterAddress on the Environments > Clusters > ClusterName > Configuration > General page of the WebLogic Server Administration Console.

• If there are fewer Managed Servers available in the cluster than the value of NumberOfServersInClusterAddress, the dynamically generated cluster address contains a ListenAddress:ListenPort combination for each of the running Managed Servers.

• If there are more Managed Servers available in the cluster than the value of NumberOfServersInClusterAddress, WebLogic Server randomly selects a subset of the available instances that is equal to the value of NumberOfServersInClusterAddress, and uses the ListenAddress:ListenPort combination for those instances to form the cluster address.

The order in which the ListenAddress:ListenPort combinations appear in the cluster address is random; from request to request, the order will vary.

Explicitly Defining Cluster Address for Production Environments

If you explicitly define a cluster address for a cluster in a production environment, specify the cluster address as a DNS name that maps to the IP addresses or DNS names of each WebLogic Server instance in the cluster.

If you define the cluster address as a DNS name, the listen ports for the cluster members are not specified in the cluster address—it is assumed that each Managed Server in the cluster has the same listen port number. Because each server instance in a cluster must have a unique combination of address and listen port, if a cluster address is a DNS name, each server instance in the cluster must have:

• a unique address and

• the same listen port number

When clients obtain an initial JNDI context by supplying the cluster DNS name, weblogic.jndi.WLInitialContextFactory obtains the list of all addresses that are mapped to the DNS name. This list is cached by WebLogic Server instances, and new initial context requests are fulfilled using addresses in the cached list with a round-robin algorithm. If a server instance in the cached list is unavailable, it is removed from the list. The address list is refreshed from the DNS service only if the server instance is unable to reach any address in its cache.

Using a cached list of addresses avoids certain problems with relying on DNS round-robin alone. For example, DNS round-robin continues using all addresses that have been mapped to the domain name, regardless of whether or not the addresses are reachable. By caching the address list, WebLogic Server can remove addresses that are unreachable, so that connection failures aren't repeated with new initial context requests.

Note:

The Administration Server should not participate in a cluster. Ensure that the Administration Server's IP address is not included in the cluster-wide DNS name. See Administration Server Considerations.

Explicitly Defining Cluster Address for Development and Test Environments

If you explicitly define a cluster address for using it in development environments, you can use a cluster DNS name for the cluster address, as described in Explicitly Defining Cluster Address for Production Environments.

Alternatively, you can define the cluster address as a list that contains the DNS name (or IP address) and listen port of each Managed Server in the cluster, as shown in the examples below:

DNSName1:port1,DNSName1:port2,DNSName1:port3
IPaddress1:port1,IPaddress2:port2;IPaddress3:port3 

Note:

Each cluster member has a unique address and port combination.

Explicitly Defining Cluster Address for Single, Multihomed Machine

If your cluster runs on a single, multihomed machine, and each server instance in the cluster uses a different IP address, define the cluster address using a DNS name that maps to the IP addresses of the server instances in the cluster. If you define the cluster address as a DNS name, specify the same listen port number for each of the Managed Servers in the cluster.

Cluster Implementation Procedures

The following sections describe how to get a clustered application up and running from the installation of the WebLogic Server through the initial deployment of application components.

• Configuration Roadmap
  
• Install WebLogic Server
  
• Create a Clustered Domain
  
• Configure Node Manager
  
• Configure Load Balancing Method for EJBs and RMIs
  
• Specifying a Timeout Value For RMIs
  
• Configure Server Affinity for Distributed JMS Destinations
  
• Configuring Load Balancers that Support Passive Cookie Persistence
  
• Configure Proxy Plug-Ins
  
• Configure Replication Groups
  
• Configure Migratable Targets for Pinned Services
  
• Package Applications for Deployment
  
• Deploy Applications
  
• Deploying, Activating, and Migrating Migratable Services
  
• Configure In-Memory HTTP Replication
  
• Additional Configuration Topics
  

Configuration Roadmap

This section lists typical cluster implementation tasks, and highlights key configuration considerations. The exact process you follow is driven by the unique characteristics of your environment and the nature of your application. The following list describes the cluster implementation tasks:

1. Install WebLogic Server

2. Create a Clustered Domain

3. Configure Node Manager

4. Configure Load Balancing Method for EJBs and RMIs

5. Configure Server Affinity for Distributed JMS Destinations

6. Configuring Load Balancers that Support Passive Cookie Persistence

7. Configure Proxy Plug-Ins

8. Configure Replication Groups

9. Configure Migratable Targets for Pinned Services

10. Package Applications for Deployment

11. Deploy Applications

12. Deploying_ Activating_ and Migrating Migratable Services

13. Configure In-Memory HTTP Replication

14. Additional Configuration Topics

Not every step is required for every cluster implementation. Additional steps may be necessary in some cases.

Install WebLogic Server

If you have not installed WebLogic Server prior, install it. For more information about WebLogic Server installation, see Planning the Oracle WebLogic Server Installation in Installing and Configuring Oracle WebLogic Server and Coherence.

• If the cluster will run on a single machine, do a single installation of WebLogic Server under the /Oracle directory to use for all clustered instances.

• For remote, networked machines, install the same version of WebLogic Server on each machine. Each machine:

  • Must have permanently assigned, static IP addresses. You cannot use dynamically-assigned IP addresses in a clustering environment.

  • Must be accessible to clients. If the server instances are behind a firewall and the clients are in front of the firewall, each server instance must have a public IP address that can be reached by the clients.

  • Must be located on the same LAN and must be reachable via IP multicast.

Create a Clustered Domain

The are multiple methods of creating a clustered domain. See Methods of Configuring Clusters.

For instructions to create a cluster using the:

• Configuration Wizard, do the following:

  1. For instructions on creating a domain, see Creating a WebLogic Domain in Creating WebLogic Domains Using the Configuration Wizard.
  2. For instructions on configuring a cluster, see Clusters in Creating WebLogic Domains Using the Configuration Wizard.

• WebLogic Server Administration Console, see Create and configure clusters in Oracle WebLogic Server Administration Console Online Help.

• Starting a WebLogic Server Cluster
  

Starting a WebLogic Server Cluster

There are multiple methods of starting a cluster. The available options include the command-line interface, scripts that contain the necessary commands, and Node Manager.

Note:

Node Manager eases the process of starting servers, and restarting them after failure.

To use Node Manager, you must first configure a Node Manager process on each machine that hosts Managed Servers in the cluster. See Configure Node Manager.

Regardless of the method you use to start a cluster, start the Administration Server first, then start the Managed Servers in the cluster.

Follow the instructions below to start the cluster from a command shell.

Note:

Each server instance is started in a separate command shell.

1. Open a command shell.
2. Change directory to the domain directory that you created with the Configuration Wizard.
3. Type the StartWebLogic command to start the Administration Server.
4. Enter user name and password for the domain when prompted.

   The command shell displays messages that report the status of the startup process.

5. Open another command shell so that you can start a Managed Server.
6. Change directory to the domain directory that you created with the Configuration Wizard.
7. Type the following command:
   StartManagedWebLogic server_name address:port

   where:

   server_name is the name of the Managed Server you wish to start

   address is the IP address or DNS name for the Administration Server for the domain

   port is the listen port for the Administration Server for the domain

8. Enter user name and password for the domain when prompted.

   The command shell displays messages that report the status of the startup process.

   Note:

   After you start a Managed Server, it listens for heartbeats from other running server instances in the cluster. The Managed Server builds its local copy of the cluster-wide JNDI tree, as described in How WebLogic Server Updates the JNDI Tree, and displays status messages when it has synchronized with each running Managed Server in the cluster. The synchronization process can take a minute or so.

9. To start another server instance in the cluster, return to step 5 and continue through step 8.
10. When you have started all Managed Servers in the cluster, the cluster startup process is complete.

Configure Node Manager

Node Manager is a standalone program provided with WebLogic Server that is useful for starting a Managed Server that resides on a different machine than its Administration Server. Node Manager also provides features that help increase the availability of Managed Servers in your cluster. For instructions to configure and use Node Manager, see Administering Node Manager for Oracle WebLogic Server.

Configure Load Balancing Method for EJBs and RMIs

Follow the instructions in this section to select the load balancing algorithm for EJBs and RMI objects.

Unless you explicitly specify otherwise, WebLogic Server uses the round-robin algorithm as the default load balancing strategy for clustered object stubs. To understand alternative load balancing algorithms, see Load Balancing for EJBs and RMI Objects. To change the default load balancing algorithm, do as follows:

1. Open the WebLogic Server Administration Console.
2. Select Environments > Clusters.
3. Select the name of your cluster in the table.
4. If you have not already done so, click Lock & Edit in the top left corner of the Console.
5. Enter the desired load balancing algorithm in the Default Load Algorithm field.
6. Select Advanced.
7. Enter the desired value in the Service Age Threshold field.
8. Click Save to save your changes.
9. Click Activate Changes in the top left corner once you are ready to activate your changes.

Specifying a Timeout Value For RMIs

You can enable a timeout option when making calls to the ReplicationManager by setting the ReplicationTimeoutEnabled in the ClusterMBean to true.

The timeout value is equal to the multicast heartbeat timeout. Although you can customize the multicast timeout value, the ReplicationManager timeout cannot be changed. This restriction exists because the ReplicationManager timeout does not affect cluster membership. A missing multicast heartbeat causes the member to be removed from the cluster and the timed out ReplicationManager call will choose a new secondary server to connect to.

Note:

It is possible that a cluster member will continue to send multicast heartbeats, but will be unable to process replication requests. This could potentially cause an uneven distribution of secondary servers. When this situation occurs, a warning message is recorded in the server logs.

Configure Server Affinity for Distributed JMS Destinations

To understand the server affinity support provided by WebLogic Server for JMS, see Load Balancing for JMS.

Configuring Load Balancers that Support Passive Cookie Persistence

Load balancers that support passive cookie persistence can use information from the WebLogic Server session cookie to associate a client with the WebLogic Server instance that hosts the session. The session cookie contains a string that the load balancer uses to identify the primary server instance for the session.

For a discussion of external load balancers, session cookie persistence, and the WebLogic Server session cookie, see Load Balancing HTTP Sessions with an External Load Balancer.

To configure the load balancer to work with your cluster, use the facilities of the load balancer to define the offset and length of the string constant.

Assuming that the Session ID portion of the session cookie is the default length of 52 bytes, on the load balancer, set:

• string offset to 53 bytes, the default Random Session ID length plus 1 byte for the delimiter character.

• string length to 10 bytes.

If your application or environmental requirements dictate that you change the length of the Random Session ID from its default value of 52 bytes, set the string offset on the load balancer accordingly. The string offset must equal the length of the Session ID plus 1 byte for the delimiter character.

Note:

For vendor-specific instructions for configuring Big-IP load balancers, see Configuring BIG-IP Hardware with Clusters.

Configure Proxy Plug-Ins

Refer to the instructions in this section if you wish to load balance servlets and JSPs using a proxy plug-in. A proxy plug-in proxies requests from a Web server to WebLogic Server instances in a cluster, and provides load balancing and failover for the proxied HTTP requests.

For information about load balancing using proxy plug-ins, see Load Balancing with a Proxy Plug-in. For information about connection and failover using proxy plug-ins, see Replication and Failover for Servlets and JSPs , and Accessing Clustered Servlets and JSPs Using a Proxy.

• If you use WebLogic Server as a Web server, set up HttpClusterServlet using the instructions in Set Up the HttpClusterServlet.

• If you use a supported third-party Web server, set up a product-specific plug-in (for a list of supported Web servers, see Load Balancing with a Proxy Plug-in) follow the instructions in Using Oracle WebLogic Server Proxy Plug-Ins.

  Note:

  Each Web server that proxies requests to a cluster must have an identically configured plug-in.

• Set Up the HttpClusterServlet
  

Set Up the HttpClusterServlet

To use the HTTP cluster servlet, configure it as the default Web application on your proxy server machine, as described in the steps below. For an introduction to Web applications, see Understanding Web Applications, Servlets, and JSPs in Developing Web Applications, Servlets, and JSPs for Oracle WebLogic Server.

1. If you have not already done so, configure a separate, non-clustered Managed Server to host the HTTP Cluster Servlet.

2. Create the web.xml deployment descriptor file for the servlet. This file must reside in the \WEB-INF subdirectory of the Web application directory. A sample deployment descriptor for the proxy servlet is provided in Sample web.xml.

   1. Define the name and class for the servlet in the <servlet> element in web.xml. The servlet name is HttpClusterServlet. The servlet class is weblogic.servlet.proxy.HttpClusterServlet.

   2. Identify the clustered server instances to which the proxy servlet will direct requests in the <servlet> element in web.xml, by defining the WebLogicCluster parameter.

   3. Optionally, define the following <KeyStore> initialization parameters to use two-way SSL with your own identity certificate and key. If no <KeyStore> is specified in the deployment descriptor, the proxy will assume one-way SSL.

      • <KeyStore>—The key store location in your Web application.

      • <KeyStoreType>—The key store type. If it is not defined, the default type will be used instead.

      • <PrivateKeyAlias>—The private key alias.

      • <KeyStorePasswordProperties>—A property file in your Web application that defines encrypted passwords to access the key store and private key alias. The file contents looks like this:

        KeyStorePassword={AES}yWv/i0qhfM4/IvzoghzjHj/xpJUkQPF8OWuSfh0f0Ss=
        PrivateKeyPassword={AES}wr86u9Z5DHr+5p7WIbzTDSy4M/sl7EYnX/K5xzcarDQ=
        

        You must use the weblogic.security.Encrypt command-line utility to encrypt the password. For more information on the Encrypt utility, as well as the CertGen, and der2pem utilities, see Using the Oracle WebLogic Server Java Utilities in the Command Reference for Oracle WebLogic Server.

   4. Create <servlet-mapping> stanzas to specify the requests that the servlet will proxy to the cluster, using the <url-pattern> element to identify specific file extensions, for example *.jsp, or *.html. Define each pattern in a separate <servlet-mapping> stanza.

      You can set the <url-pattern> to "/" to proxy any request that cannot be resolved by WebLogic Server to the remote server instance. If you do so, you must also specifically map the following extensions: *.jsp, *.htm, and *.html, to proxy files ending with those extensions. For an example, see Sample web.xml.

   5. You can enable the WLProxyPassThrough attribute to allow the header to be passed through a chain of proxies and the WLProxySSLPassThrough attribute so that the use of SSL is passed on to WebLogic Server. For a complete description of these attributes, see General Parameters for Web Server Plug-Ins in Using Oracle WebLogic Server Proxy Plug-Ins.

   6. Define, as appropriate, any additional parameters. See Table 10-1 for a list of key parameters. See Parameters for Web Server Plug-ins in Using Oracle WebLogic Server Proxy Plug-Ins for a complete list. Follow the syntax instructions in Proxy Servlet Deployment Parameters.

3. Create the weblogic.xml deployment descriptor file for the servlet. This file must reside in the \WEB-INF subdirectory of the Web application directory.

   Assign the proxy servlet as the default Web application for the Managed Server on the proxy machine by setting the <context-root> element to a forward slash character (/) in the <weblogic-web-app> stanza. For an example, see Sample weblogic.xml.

4. In the WebLogic Server Administration Console, deploy the servlet to the Managed Server on your proxy server machine. For instructions, see Deploy applications and modules in Oracle WebLogic Server Administration Console Online Help.

• Sample web.xml
  
• Sample weblogic.xml
  
• Proxy Servlet Deployment Parameters
  
• Accessing Applications Via the Proxy Server
  

Sample web.xml

This section contains a sample deployment descriptor file (web.xml) for HttpClusterServlet.

web.xml defines parameters that specify the location and behavior of both versions of the proxy servlet.

• The DOCTYPE stanza specifies the document type definition (DTD) used by WebLogic Server to validate web.xml.

• The servlet stanza:

  • Specifies the location of the proxy plug-in servlet class. The file is located in the weblogic.jar in your WL_HOME/server/lib directory. You do not have to specify the servlet's full directory path in web.xml because weblogic.jar is put in your CLASSPATH when you start WebLogic Server.

  • Identifies the host name (either DNS name or IP address) and listen port of each Managed Servers in the cluster, using the WebLogicCluster parameter.

  • Identifies the key store initialization parameters to use two-way SSL with your own identity certificate and key.

• The three servlet-mapping stanzas specify that the servlet will proxy URLs that end in '/', 'htm', 'html', or 'jsp' to the cluster.

For parameter definitions, see Proxy Servlet Deployment Parameters.

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee 
         http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"version="3.1">
<servlet>
  <servlet-name>HttpClusterServlet</servlet-name> 
    <servlet-class>
      weblogic.servlet.proxy.HttpClusterServlet
    </servlet-class>
  <init-param>
    <param-name>WebLogicCluster</param-name>
    <param-value>hostname1:7736|hostname2:7736|hostname:7736</param-value> 
  </init-param>
  <init-param>
    <param-name>KeyStore</param-name>
    <param-value>/mykeystore</param-value>
  </init-param>
  <init-param>
    <param-name>KeyStoreType</param-name>
    <param-value>jks</param-value>
  </init-param>
  <init-param>
    <param-name>PrivateKeyAlias</param-name>
    <param-value>passalias</param-value>
  </init-param>
  <init-param>
    <param-name>KeyStorePasswordProperties</param-name>
    <param-value>mykeystore.properties</param-value>
  </init-param>
</servlet>
<servlet-mapping>
  <servlet-name>HttpClusterServlet</servlet-name>
  <url-pattern>/</url-pattern>
</servlet-mapping>
<servlet-mapping>
  <servlet-name>HttpClusterServlet</servlet-name> 
  <url-pattern>*.jsp</url-pattern> 
</servlet-mapping>	
<servlet-mapping>
  <servlet-name>HttpClusterServlet</servlet-name> 
  <url-pattern>*.htm</url-pattern> 
</servlet-mapping>
<servlet-mapping>
  <servlet-name>HttpClusterServlet</servlet-name> 
  <url-pattern>*.html</url-pattern> 
</servlet-mapping>
</web-app>

Sample weblogic.xml

This section contains a sample weblogic.xml file. The <context-root> deployment parameter is set to "/". This makes the proxy servlet the default Web application for the proxy server.

<!DOCTYPE weblogic-web-app PUBLIC "-//BEA Systems, Inc.//DTD Web Application 9.1//EN" "http://www.bea.com/servers/wls810/dtd/weblogic
810-web-jar.dtd">
  <weblogic-web-app>
    <context-root>/</context-root>
  </weblogic-web-app>

Proxy Servlet Deployment Parameters

Key parameters for configuring the behavior of the proxy servlet in web.xml are listed in Before You Start.

The parameters for the proxy servlet are the same as those used to configure WebLogic Server plug-ins for Apache, Microsoft, and Netscape Web servers. For a complete list of parameters for configuring the proxy servlet and the plug-ins for third-part Web servers, see Parameters for Web Server Plug-ins in Using Oracle WebLogic Server Proxy Plug-Ins.

The syntax for specifying the parameters, and the file where they are specified, is different for the proxy servlet and for each of the plug-ins.

For the proxy servlet, specify the parameters in web.xml, each in its own <init-param> stanza within the <servlet> stanza of web.xml. For example:

<init-param> 
    <param-name>ParameterName</param-name> 
    <param-value>ParameterValue</param-value> 
</init-param>

Table 10-1 Proxy Servlet Deployment Parameter

Parameter	Usage
WebLogicCluster	<init-param> <param-name>WebLogicCluster</param-name> <param-value>WLS1.com:port|WLS2.com:port </param-value> Where WLS1.com and WLS2.com are the host names of servers in the cluster, and port is a port where the host is listening for HTTP requests. If you are using SSL between the plug-in and WebLogic Server, set the port number to the SSL listen port (see Configuring the Listen Port) and set the SecureProxy parameter to ON.
SecureProxy	<init-param> <param-name>SecureProxy</param-name> <param-value>ParameterValue</param-value> </init-param> Valid values are ON and OFF. If you are using SSL between the plug-in and WebLogic Server, set the port number to the SSL listen port (see Configuring the Listen Port) and set the SecureProxy parameter to ON.
DebugConfigInfo	<init-param> <param-name>DebugConfigInfo</param-name> <param-value>ParameterValue</param-value> </init-param> Valid values are ON and OFF. If set to ON, you can query the HttpClusterServlet for debugging information by adding a request parameter of ?__WebLogicBridgeConfig to any request. (Note: There are two underscore ( _ ) characters after the ?.) For security reasons, it is recommended that you set the DebugConfigInfo parameter to OFF in a production environment.
ConnectRetrySecs	Interval in seconds that the servlet will sleep between attempts to connect to a server instance. Assign a value less than ConnectTimeoutSecs. The number of connection attempts the servlet makes before returning an HTTP 503/Service Unavailable response to the client is ConnectTimeoutSecs divided by ConnectRetrySecs. Syntax: <init-param> <param-name>ConnectRetrySecs</param-name> <param-value>ParameterValue</param-value> </init-param>
ConnectTimeoutSecs	Maximum time in seconds that the servlet will attempt to connect to a server instance. Assign a value greater than ConnectRetrySecs. If ConnectTimeoutSecs expires before a successful connection, an HTTP 503/Service Unavailable response is sent to the client. Syntax: <init-param> <param-name>ConnectTimeoutSecs</param-name> <param-value>ParameterValue</param-value> </init-param>
PathTrim	String trimmed by the plug-in from the beginning of the original URL, before the request is forwarded to the cluster. Syntax: <init-param> <param-name>PathTrim</param-name> <param-value>ParameterValue</param-value> </init-param> Example: If the URL http://myWeb.example.com/weblogic/foo is passed to the plug-in for parsing and if PathTrim has been set to /weblogic the URL forwarded to WebLogic Server is: http://myWeb.example.com:7001/foo
TrimExt	The file extension to be trimmed from the end of the URL. Syntax: <init-param> <param-name>TrimExt</param-name> <param-value>ParameterValue</param-value> </init-param>
clientCertProxy	Specifies to trust client certificates in the WL-Proxy-Client-Cert header. Valid values are true and false. The default value is false. This setting is useful if user authentication is performed on the proxy server—setting clientCertProxy to true causes the proxy server to pass on the certs to the cluster in a special header, WL-Proxy-Client-Cert. The WL-Proxy-Client-Cert header can be used by any client with direct access to WebLogic Server. WebLogic Server takes the certificate information from that header, trusting that is came from a secure source (the plug-in) and uses that information to authenticate the user. For this reason, if you set clientCertProxy to true, use a connection filter to ensure that WebLogic Server accepts connections only from the machine on which the plug-in is running. See Using Network Connection Filters in Developing Applications with the WebLogic Security Service.
PathPrepend	String that the servlet prepends to the original URL, after PathTrim is trimmed, before forwarding the URL to the cluster. <init-param> <param-name>PathPrepend</param-name> <param-value>ParameterValue</param-value> </init-param>
RoutingHandlerClassName	Extends the proxy servlet to support Web service cluster routing. See Managing Web Services in a Cluster in Developing JAX-WS Web Services for Oracle WebLogic Server. <init-param> <param-name>RoutingHandlerClassName</param-name> <param-value> weblogic.wsee.jaxws.cluster.proxy.SOAPRoutingHandler </param-value> </init-param>

Accessing Applications Via the Proxy Server

Ensure that application clients access through the proxy server are deployed to your cluster. Address client requests to the listen address and listen port of the proxy server.

If you have problems:

• Ensure that all server instances have unique address/port combinations.

  Each of the server instances in the configuration must have a unique combination of listen address and listen port.

• Ensure that the proxy servlet is the default application for the proxy server.

  If you get "page not found" error when you try to your application, make sure that weblogic.xml is in \WEB-INF for the application and that it sets the context-root deployment parameter to "/".

• When all else fails, restart

  If you are having problems, try to restart all your servers. Some of the changes you made while configuring your setup may not persist to the configuration file.

• Verify Your Configuration

  To verify the configuration of the HttpClusterServlet:

  1. Set the DebugConfigInfo parameter in web.xml to ON.

  2. Use a Web browser to access the following URL:

     http://myServer:port/placeholder.jsp?__WebLogicBridgeConfig
     

  Where:

  • myServer is the Managed Server on the proxy machine where HttpClusterServlet runs,

  • port is the port number on the server that is listening for HTTP requests, and

  • placeholder.jsp is a file that does not exist on the server.

  The plug-in gathers configuration information and run-time statistics and returns the information to the browser. For more information, see Parameters for Web Server Plug-ins in Using Oracle WebLogic Server Proxy Plug-Ins.

Configure Replication Groups

To support automatic failover for servlets and JSPs, WebLogic Server replicates HTTP session states in memory. You can further control where secondary states are placed using replication groups. A replication group is a preferred list of clustered instances to be used for storing session state replicas.

If your cluster will host servlets or stateful session EJBs, you may want to create replication groups of WebLogic Server instances to host the session state replicas.

For instructions on how to determine which server instances should participate in each replication group, and to determine each server instance's preferred replication group, follow the instructions in Using Replication Groups.

Then follow these steps to configure replication groups for each WebLogic Server instance:

1. Open the WebLogic Server Administration Console.
2. Select Environments > Servers.
3. In the table, select the name of the server you want to configure.
4. Select the Cluster page.
5. If you have not already done so, click Lock & Edit in the top left corner of the Console.
6. Enter values for the following attribute fields:

   • Replication Group: Enter the name of the replication group to which this server instance belongs.

   • Preferred Secondary Group: Enter the name of the replication group you would like to use to host replicated HTTP session states for this server instance.

7. Click Save to save your changes.
8. Click Activate Changes in the top left corner to activate your changes.

Configure Migratable Targets for Pinned Services

WebLogic Server enables you to configure an optional migratable target, which is a special target that can migrate from one server in a cluster to another. As such, a migratable target provides a way to group pinned services that should move together. When the migratable target is migrated, all services hosted by that target are migrated. Pinned services include JMS-related services (for example, JMS servers, SAF agents, path services, and persistent stores) or the JTA Transaction Recovery Service.

If you want to use a migratable target, configure the target server list before deploying or activating the service in the cluster. If you do not configure a migratable target in the cluster, migratable services can be migrated to any available WebLogic Server instance in the cluster. See Understanding Migratable Targets In a Cluster.

Package Applications for Deployment

You must package applications before you deploy them to WebLogic Server. For more information ,see Packaging Applications Using wlpackage in Developing Applications for Oracle WebLogic Server.

Deploy Applications

Clustered objects in WebLogic Server should be deployed homogeneously. To ensure homogeneous deployment, when you select a target, use the cluster name rather than individual WebLogic Server instances in the cluster. If cluster is dynamic or mixed cluster type, you can select singleton or distributed deployment based on your need for one single instance across entire cluster or one instance per cluster member.

The Console automates deploying replica-aware objects to clusters. When you deploy an application or object to a cluster, the Console automatically deploys it to all members of the cluster (whether they are local to the Administration Server machine or they reside on remote machines). For a discussion of application deployment in clustered environments, see Methods of Configuring Clusters. For a broad discussion of deployment topics, see Deploying Applications to Oracle WebLogic Server.

Note:

All server instances in your cluster should be running when you deploy applications to the cluster using the WebLogic Server Administration Console.

• Deploying to a Single Server Instance (Pinned Deployment)
  
• Cancelling Cluster Deployments
  
• Viewing Deployed Applications
  
• Undeploying Deployed Applications
  

Deploying to a Single Server Instance (Pinned Deployment)

Deploying a application to a server instance, rather than the all cluster members is called a pinned deployment. Although a pinned deployment targets a specific server instance, all server instances in the cluster must be running during the deployment process.

You can perform a pinned deployment using the WebLogic Server Administration Console or using the command line weblogic.Deployer.

• Pinned Deployment from the Command Line
  

Pinned Deployment from the Command Line

From a command shell, use the following syntax to target a server instance:

java weblogic.Deployer -activate -name ArchivedEarJar -source C:/MyApps/JarEar.ear -target server1

Cancelling Cluster Deployments

You can cancel a deployment using the WebLogic Server Administration Console or using the command line weblogic.Deployer.

• Cancel Deployment from the Command Line
  
• Cancel Deployment Using the WebLogic Server Administration Console
  

Cancel Deployment from the Command Line

From a command shell, use the following syntax to cancel the deployment task ID:

java weblogic.Deployer -adminurl http://admin:7001 -cancel -id tag

Cancel Deployment Using the WebLogic Server Administration Console

In the WebLogic Server Administration Console, open the Tasks node to view and to cancel any current deployment tasks.

Viewing Deployed Applications

To view a deployed application in the WebLogic Server Administration Console:

1. In the WebLogic Server Administration Console, select Deployments.
2. View a list of deployed applications in the table.

Undeploying Deployed Applications

To undeploy a deployed application from the WebLogic Server Administration Console, do as follows:

1. In the WebLogic Server Administration Console, select Deployments.
2. In the table, select the check box to the left of the application you want to undeploy.
3. If you have not already done so, click Lock & Edit in the top left corner of the Console.
4. Click Stop when you want the application to stop (undeploy).
5. Click Yes.
6. Click Activate Changes in the top left corner of the Console to activate your changes.

Deploying, Activating, and Migrating Migratable Services

The sections that follow provide guidelines and instructions for deploying, activating, and migrating migratable services.

• Deploying JMS to a Migratable Target Server Instance
  
• Activating JTA as a Migratable Service
  
• Migrating a Pinned Service to a Target Server Instance
  

Deploying JMS to a Migratable Target Server Instance

The migratable target that you create defines the scope of server instances in the cluster that can potentially host a migratable service. You must deploy or activate a pinned service on one of the server instances listed in the migratable target to migrate the service within the target server list at a later time. Use the instructions that follow to deploy a JMS service on a migratable target, or activate the JTA transaction recovery system so that you can migrate it later.

Note:

If you did not configure a migratable target, deploy the JMS server to any WebLogic Server instance in the cluster; you can then migrate the JMS server to any other server instance in the cluster (no migratable target is used).

Before you begin, use the instructions in Configure Migratable Targets for Pinned Services, to create a migratable target for the cluster. Then, deploy JMS-related services to a migratable target, as described in the following topics of Oracle WebLogic Server Administration Console Online Help:

• Change JMS server targets

• Change SAF agent targets

• Change path service targets

• Create file stores and Create JDBC stores

Activating JTA as a Migratable Service

The JTA recovery service is automatically started on one of the server instances listed in the migratable target for the cluster; you do not have to deploy the service to a selected server instance.

If you did not configure a JTA migratable target, WebLogic Server activates the service on any available WebLogic Server instance in the cluster. For instructions to change the current server instance that hosts the JTA service, see Migrating a Pinned Service to a Target Server Instance.

Migrating a Pinned Service to a Target Server Instance

After you have deployed a migratable service, you can use the WebLogic Server Administration Console to manually migrate the service to another server instance in the cluster. If you configured a migratable target for the service, you can migrate to any other server instance listed in the migratable target, even if that server instance is not currently running. If you did not configure a migratable target, you can migrate the service to any other server instance in the cluster.

If you migrate a service to a stopped server instance, the server instance will activate the service upon the next startup. If you migrate a service to a running WebLogic Server instance, the migration takes place immediately.

Before you begin, use the instructions in Deploying JMS to a Migratable Target Server Instance, to deploy a pinned service to the cluster. Next, migrate the pinned service using the WebLogic Server Administration Console by following the appropriate instructions in the Oracle WebLogic Server Administration Console Online Help:

• Manually migrate JMS-related services

• Manually migrate the Transaction Recovery Service

Here are some additional steps that are not covered in the Console Help instructions:

1. If the current server is not reachable by the Administration Server, the WebLogic Server Administration Console displays this message:

   Unable to contact server MyServer-1, the source server from which services are being migrated.
   Please ensure that server MyServer-1 is NOT running! If the administration
   server cannot reach server MyServer-1 due to a network partition, inspect the
   server directly to verify that it is not running. Continue the migration only
   if MyServer-1 is not running. Cancel the migration if MyServer-1 is running,
   or if you do not know whether it is running.

   If this message is displayed, perform the procedure described in Migrating When the Currently Active Host is Unavailable.

2. If the Destination Server is stopped, the WebLogic Server Administration Console notifies you of the stopped server instance and asks if you would like to continue the migration. Click the Continue button to migrate to the stopped server instance, or click Cancel to stop the migration and select a different server instance.
3. The migration process may take several minutes to complete, depending on the server instance configuration. However, you can continue using other WebLogic Server Administration Console features while the migration takes place. To view the migration status at a later time, click the Tasks node in the left pane to display the currently-running tasks for the domain; then select the task description for the migration task to view the current status.

• Migrating When the Currently Active Host is Unavailable
  

Migrating When the Currently Active Host is Unavailable

Use this migration procedure if a clustered Managed Server that was the active server for the migratable service crashes or becomes unreachable.

This procedure purges the failed Managed Server's configuration cache. The purpose of purging the cache is to ensure that, when the failed server instance is once again available, it does not re-deploy a service that you have since migrated to another Managed Server. Purging the cache eliminates the risk that Managed Server which was previously the active host for the service uses local, out-of-date configuration data when it starts up again.

1. Disconnect the machine from the network entirely. It should not be accessible to the Administration Server or client traffic. If the machine has a dual ported disk, disconnect it.
2. Migrate the migratable service(s) to a Managed Server instance on a different machine. The Administration Server must be running, so that it can coordinate the migration and update the activation table.

   • If you use the command line for migration, use the -sourcedown flag.

   • If you use the Console, it will ask you to make sure the source server is not going to restart.

   The migratable service is now available on a different Managed Server on a different machine. The following steps can be performed at leisure.

3. Perform the necessary repair or maintenance on the failed machine.
4. Restart the machine, but do not connect it to the network.

   Node Manager will start as a service or daemon, and will attempt to start the Managed Servers on the machine.

   • If Managed Server Independence is enabled, the Managed Server will start, even though it cannot connect to the Administration Server.

   • If Managed Server Independence is disabled, the Managed Server will not start, because it cannot connect to the Administration Server.

5. Reconnect the machine to the network and shared storage, including dual ported disk, if applicable.
6. Restart the Node Manager daemon/service or restart the machine, to start all remaining Managed Servers.
7. Start the Managed Server that was disabled. This is a normal start up, rather than a restart performed by Node Manager. The Administration Server must be reachable and running, so that the Managed Servers can synchronize with the migratable service activation table on the Administration Server and hence know that it is no longer the active host of the migratable service.

Configure In-Memory HTTP Replication

To support automatic failover for servlets and JSPs, WebLogic Server replicates HTTP session states in memory.

Note:

WebLogic Server can also maintain the HTTP session state of a servlet or JSP using file-based or JDBC-based persistence. For more information on these persistence mechanisms, see Using Sessions and Session Persistence in Developing Web Applications, Servlets, and JSPs for Oracle WebLogic Server.

In-memory HTTP session state replication is controlled separately for each application you deploy. For the application, the parameter that controls it is PersistentStoreType, which appears within the session-descriptor element in the WebLogic deployment descriptor file and weblogic.xml.

domain_directory/applications/application_directory/WEB-INF/weblogic.xml

To use in-memory HTTP session state replication across server instances in a cluster, set the PersistentStoreType to replicated. The fragment below shows the appropriate XML from weblogic.xml.

<session-descriptor>
<persistent-store-type>replicated</persistent-store-type> 
</session-descriptor>

Additional Configuration Topics

The sections below contain useful tips for particular cluster configurations.

• Configure IP Sockets
  
• Configure Multicast Time-To-Live (TTL)
  
• Configure Multicast Buffer Size
  
• Configure Multicast Data Encryption
  
• Configure Machine Names
  
• Configuration Notes for Multitier Architecture
  
• Enable URL Rewriting
  

Configure IP Sockets

For best socket performance, Oracle recommends that you use the native socket reader implementation, rather than the pure-Java implementation, on machines that host WebLogic Server instances.

If you must have to use the pure-Java socket reader implementation for host machines, you can still improve the performance of socket communication by configuring the proper number of socket reader threads for each server instance and client machine.

• To learn more about how IP sockets are used in a cluster, and why native socket reader threads provide best performance, see Peer-to-Peer Communication Using IP Sockets, and Client Communication via Sockets.

• For instructions to determine the number of socket reader threads necessary for your cluster, see Determining Potential Socket Usage. If you are deploying a servlet cluster in a multitier cluster architecture, this has an effect on how many sockets you require, as described in Configuration Considerations for Multitier Architecture.

The following sections have instructions to configure native socket reader threads for host machines and set the number of reader threads for host and client machines.

• Configure Native IP Sockets Readers on Machines that Host Server Instances
  
• Set the Number of Reader Threads on Machines that Host Server Instances
  
• Set the Number of Reader Threads on Client Machines
  

Configure Native IP Sockets Readers on Machines that Host Server Instances

To configure a WebLogic Server instance to use the native socket reader threads implementation:

1. Open the WebLogic Server Administration Console.
2. Select Environments > Servers.
3. Select the name of the server instance you want to configure.
4. If you have not already done so, click Lock & Edit in the top left corner of the Console.
5. Select Configuration > Tuning.
6. Select the Enable Native IO check box.
7. Click Save.
8. Click Activate Changes in the top left corner of the Console to activate your changes.

Set the Number of Reader Threads on Machines that Host Server Instances

By default, a WebLogic Server instance creates three socket reader threads upon starting. If you determine that your cluster system may utilize more than three sockets during peak periods, increase the number of socket reader threads by using the following instructions:

1. Open the WebLogic Server Administration Console.
2. Select Environments > Servers.
3. Select the name of the server instance you want to configure.
4. If you have not already done so, click Lock & Edit in the top left corner of the Console.
5. Select Configuration > Tuning.
6. Edit the percentage of Java reader threads in the Socket Readers field. The number of Java socket readers is computed as a percentage of the number of total execute threads (as shown in the Execute Threads field).
7. Click Save to save your changes.
8. Click Activate Changes in the top left corner of the Console to activate your changes.

Set the Number of Reader Threads on Client Machines

On client machines, you can configure the number of socket reader threads in the Java Virtual Machine (JVM) that runs the client. Specify the socket readers by defining the -Dweblogic.ThreadPoolSize=value and -Dweblogic.ThreadPoolPercentSocketReaders=value options in the Java command line for the client.

Configure Multicast Time-To-Live (TTL)

If your cluster spans multiple subnets in a WAN, the value of the Multicast TTL parameter for the cluster must be high enough to ensure that routers do not discard multicast packets before they reach their final destination. The Multicast TTL parameter sets the number of network hops a multicast message makes before the packet can be discarded. Configuring the Multicast TTL parameter appropriately reduces the risk of losing the multicast messages that are transmitted among server instances in the cluster.

For more information about planning your network topology to ensure that multicast messages are reliably transmitted, see If Your Cluster Spans Multiple Subnets In a WAN .

To configure the Multicast TTL for a cluster, change the Multicast TTL value on the Multicast page for the cluster in the WebLogic Server Administration Console. The config.xml excerpt below shows a cluster with a Multicast TTL value of three. This value ensures that the cluster's multicast messages can pass through three routers before being discarded:

<Cluster
	Name="testcluster"
	ClusterAddress="wanclust"
	MulticastAddress="wanclust-multi"
	MulticastTTL="3"
/>

Note:

When relying upon the Multicast TTL value, it is important to remember that within a clustered environment it is possible that timestamps across servers may not always be synchronized. For example, this can occur in replicated HTTP sessions and EJBs.

When the ClusterDebug flag is enabled and cluster members clocks are not synchronized, an error is printed to the server log.

Configure Multicast Buffer Size

If multicast storms occur because server instances in a cluster are not processing incoming messages on a timely basis, you can increase the size of multicast buffers. For information on multicast storms, see If Multicast Storms Occur.

TCP/IP kernel parameters can be configured with the UNIX ndd utility. The udp_max_buf parameter controls the size of send and receive buffers (in bytes) for a UDP socket. The appropriate value for udp_max_buf varies from deployment to deployment. If you are experiencing multicast storms, increase the value of udp_max_buf by 32K, and evaluate the effect of this change.

Do not change udp_max_buf unless necessary. Before changing udp_max_buf, read the warning in the UDP Parameter With Additional Caution in Solaris Tunable Parameters Reference Manual.

Configure Multicast Data Encryption

WebLogic Server allows you to encrypt multicast messages that are sent between clusters. You can enable this option in the WebLogic Server Administration Console by following the below instructions:

1. Open the WebLogic Server Administration Console.
2. Select Environment > Clusters > cluster_name > Multicast node.
3. Select Advanced options.
4. Select Enable Multicast Data Encryption.

Only the data portion of the multicast message is encrypted. Information contained in the multicast header is not encrypted.

Configure Machine Names

Configure a machine name, if:

• Your cluster will span multiple machines, and multiple server instances will run on individual machines in the cluster.

  Or

• You plan to run Node Manager on a machine that does not host an Administration Server.

WebLogic Server uses configured machine names to determine whether or not two server instances reside on the same physical hardware. Machine names are generally used with machines that host multiple server instances. If you do not define machine names for such installations, each instance is treated as if it resides on separate physical hardware. This can negatively affect the selection of server instances to host secondary HTTP session state replicas, as described in Using Replication Groups.

Configuration Notes for Multitier Architecture

If your cluster has a multitier architecture, see the configuration guidelines in Configuration Considerations for Multitier Architecture.

Enable URL Rewriting

In its default configuration, WebLogic Server uses client-side cookies to keep track of the primary and secondary server instance that host the client's servlet session state. If client browsers have disabled cookie usage, WebLogic Server can also keep track of primary and secondary server instances using URL rewriting. With URL rewriting, both locations of the client session state are embedded into the URLs passed between the client and proxy server. To support this feature, you must ensure that URL rewriting is enabled on the WebLogic Server cluster. For instructions on how to enable URL rewriting, see Using URL Rewriting Instead of Cookies in Developing Web Applications, Servlets, and JSPs for Oracle WebLogic Server.