9 Administration Server High Availability

The Administration Server plays a unique role in domains. To set up high availability, you configure the Administration Server on a virtual host.

• Administration Server Role
  The Administration Server is the central control entity for configuring the entire domain, and manage and monitor all domain resources. It maintains domain configuration documents and distributes changes in them to Managed Servers.
• Role of Node Manager
  For each WebLogic Server domain you create, a per domain Node Manager configuration is created by default. This Node Manager comes complete with security credentials, a properties file, domain registration, and start scripts.
• Administration Server High Availability Topology
  An Administration Server can be active on one host at any one time. To set up high availability, you configure the Administration Server on a virtual host so that if the machine that it runs on fails, you can fail it over to another host in the domain.
• Configuring Administration Server High Availability
  In a highly available Administration Server environment, both hosts must have access to shared storage because the domain directory is maintained in shared storage.
• Failing Over or Failing Back Administration Server
  You fail over or fail back the Administration Server after host failure.

Administration Server Role

The Administration Server is the central control entity for configuring the entire domain, and manage and monitor all domain resources. It maintains domain configuration documents and distributes changes in them to Managed Servers.

Each domain requires one server that acts as the Administration Server. For more information on the Administration Server and Node Manager, see the following topics:

Table 9-1 Administration Server and Node Manager Topics

For information on...	See this topic...
Starting and Stopping the Administration Server	Starting and Stopping Administration Server in Administering Oracle Fusion Middleware
Configuring virtual hosting	Configuring Virtual Hosting in Administering Server Environments for Oracle WebLogic Server
Using Node Manager	In Administering Node Manager for Oracle WebLogic Server: Node Manager and System Crash Recovery How Node Manager Works in a WLS Environment Node Manager Configuration and Log Files

• Administration Server Failure and Restart
  Administration Server failure doesn't affect how Managed Servers in a domain operate.
• Shared Storage and Administration Server High Availability
  With shared storage, a backup host can access the same artifacts (Oracle binaries, configuration files, domain directory, and data) that an active host can.

Administration Server Failure and Restart

Administration Server failure doesn't affect how Managed Servers in a domain operate.

If an Administration Server fails due to a hardware or software failure on its host computer, other server instances on the same computer may also be affected.

For more information on Administration Server failure, see Impact of Managed Server Failure in Administering Oracle Fusion Middleware.

To restart an Administration Server, see What Happens if the Administration Server Fails? in Oracle Fusion Middleware Using Clusters for Oracle Server.

Shared Storage and Administration Server High Availability

With shared storage, a backup host can access the same artifacts (Oracle binaries, configuration files, domain directory, and data) that an active host can.

You configure this access by placing artifacts in storage that all hosts in the highly available Administration Server configuration can access. Shared storage is a network-attached storage (NAS) or storage area network (SAN) device. See Using Shared Storage.

Role of Node Manager

For each WebLogic Server domain you create, a per domain Node Manager configuration is created by default. This Node Manager comes complete with security credentials, a properties file, domain registration, and start scripts.

You can configure the scope of Node Manager:

• per domain Node Manager is associated with a domain to control all servers for the domain on a machine. Default configuration.

• per host Node Manager is associated with a specific machine, not a domain. One Node Manager process can control server instances in any domain, as long as the server instances reside on the same machine as the Node Manager process. A per host Node Manager must run on each computer that hosts WebLogic Server instances that you want to control with Node Manager, whether the WebLogic Server instances are an Administration Server or Managed Server(s).

Note:

Oracle recommends that you run Node Manager as an operating system service so that it restarts automatically if its host machine restarts.

Node Manager failure doesn't affect any servers running on the machine.

See What is Node Manager? in Oracle Fusion Middleware Understanding Oracle Fusion Middleware Concepts.

Administration Server High Availability Topology

An Administration Server can be active on one host at any one time. To set up high availability, you configure the Administration Server on a virtual host so that if the machine that it runs on fails, you can fail it over to another host in the domain.

Administration Server is configured to use a virtual IP to overlap the backup hosts. You configure Administration Server to listen on this virtual IP. The benefit of a virtual host and virtual IP is that you don't need to add a third machine; if failover occurs, you can map the virtual host to a surviving host in the domain by moving the virtual IP.

The two hosts share a virtual hostname and a virtual IP. However, only the active host can use this virtual IP at any one time. If the active host fails, the backup host becomes active and you must move (manually) the virtual IP to the new active host. The new active host then services all requests through the virtual IP. (You configure a high availability deployment to listen on this virtual IP.)

Figure 9-1 shows a highly available Administration Server.

In this topology, the Administration Server runs on a virtual host, APPHOST0. APPHOST0 overlaps to APPHOST1 or APPHOST2 by means of a virtual IP.

At first, APPHOST0 maps to APPHOST1. However, if the Administration Server fails due to an APPHOST1 failure, APPHOST0 fails over to APPHOST2 by moving the virtual IP.

Figure 9-1 Administration Server High Availability Topology

Description of "Figure 9-1 Administration Server High Availability Topology"

Configuring Administration Server High Availability

In a highly available Administration Server environment, both hosts must have access to shared storage because the domain directory is maintained in shared storage.

During normal operation, the Administration Server on the active host owns the domain directory in shared storage. If the active host fails, the backup host takes over and restarts the Administration Server from the shared domain directory.

• Administration Server High Availability Requirements
  To configure a highly available Administration Server, your environment must meet certain requirements.
• Configuring the Administration Server for High Availability
  To configure the Administration Server for high availability, you must start with the standard high availability topology that has one cluster (cluster_1).

Administration Server High Availability Requirements

To configure a highly available Administration Server, your environment must meet certain requirements.

• Conform to the standard installation topology. See About the Oracle Fusion Middleware Standard HA Topology and Figure 1-1.

• Include two hosts, APPHOST1 and APPHOST2, to implement a WebLogic Server cluster (cluster_1). In Configuring the Administration Server for High Availability, IP addresses for APPHOST1 and APPHOST2 are ip1 and ip2, respectively.

• APPHOST1 and APPHOST2 mount a common directory from shared storage and have read/write access rights to the directory. This directory is for installing products and storing domain directories.

• A reserved virtual IP address (vip0) to point to the host that runs the Administration Server. This floating virtual server IP address is configured dynamically on the host that the Administration Server runs on.

• Node Manager instances to manage the Administration Server and migrate it from the failed host to the designated standby host.

Configuring the Administration Server for High Availability

To configure the Administration Server for high availability, you must start with the standard high availability topology that has one cluster (cluster_1).

See About the Oracle Fusion Middleware Standard HA Topology.

To set up a highly available Administration Server, you run the Administration Server on a separate, virtual host (APPHOST0). You set up APPHOST0 so that it maps to one of the existing hosts in the cluster (APPHOST1 or APPHOST2) by configuring a (virtual) server IP for APPHOST0 on that existing host. If failover occurs, APPHOST0 fails over by moving its virtual server IP to a surviving host. The domain configuration is on shared storage so that the surviving host can access it.

Note:

There are multiple ways for Administration Server services to accomplish configuration tasks. No matter which method you use, the Administration Server must be running when you change the configuration.

Table 9-2 Host and Node Manager Terms

Term	Description
APPHOST0, machine_0	Virtual machine that the Administration Server runs on
APPHOST1, APPHOST2	Machines that host the application tier.
vip0	Virtual server IP address that the Administration Server listens on
NMa	Per-domain Node Manager that manages the Administration Server that runs on APPHOST0
NM1, NM2	Node Manager instances that run on APPHOST1 and APPHOST2, respectively
ip1, ip2	IP addresses of APPHOST1 and APPHOST2, respectively

To configure the Administration Server for high availability:

1. Configure a virtual server IP address (vip0) on APPHOST1 to represent virtual host APPHOST0.

   See Configuring Virtual Hosting in Administering Server Environments for Oracle WebLogic Server.

2. Use an Oracle Fusion Middleware expanded installation procedure to install Oracle Fusion Middleware binaries and configure the domain into a directory on shared storage. Use vip0 as the Administration Server listen address.
3. Create a virtual machine, machine_0 and add the Administration Server to it. machine_0 represents the virtual server host APPHOST0 with the IP address vip0.
4. Create a cluster (cluster_1) that has two Managed Servers, server_1 and server_2, that are assigned to machine_1 and machine_2, respectively.

   • machine_1 represents APPHOST1 and machine_2 represents APPHOST2.

   • server_1 and server_2 are set up to listen on ip1 and ip2, respectively.

5. Scale out the virtual server to APPHOST1 and APPHOST2. See Roadmap for Scaling Out Your Topology. To scale out, you pack the domain in shared storage and unpack it to a local directory on APPHOST1 and APPHOST2.
6. From APPHOST1, start a per-domain Node Manager (NMa) to manage the Administration Server listening on the configured virtual server IP vip0 on APPHOST1. Start this instance of Node Manager from the domain directory in shared storage.
7. On APPHOST1, start a per-domain Node Manager (NM1) to manage server_1 listening on ip1. Start this Node Manager (NM1) from the domain directory that you unpacked to local storage in APPHOST1 in step 5.
8. On APPHOST2, start a per-domain Node Manager (NM2) to manage server_2 listening on ip2. Start this Node Manager (NM2) from the domain directory that you unpacked to local storage in APPHOST2 step 5.
9. Use Node Manager (NMa) to start the Administration Server on APPHOST1.
10. Start Managed Servers server_1 and server_2 using NM1 and NM2, respectively.
11. Verify that the Administration Server and Managed Servers work properly. Connect to the Administration Server using the virtual IP address vip0.

Failing Over or Failing Back Administration Server

You fail over or fail back the Administration Server after host failure.

• Failing Over the Administration Server if Original Host Fails
  You fail over the Administration Server to another host if its original host (APPHOST1) fails. To do this, you configure the virtual IP address on the alternate host (APPHOST2), then start Node Manager and the Administration Server.
• Failing Back the Administration Server to the Original Host
  You fail back the Administration Server to its original host after it restarts.

Failing Over the Administration Server if Original Host Fails

You fail over the Administration Server to another host if its original host (APPHOST1) fails. To do this, you configure the virtual IP address on the alternate host (APPHOST2), then start Node Manager and the Administration Server.

To fail over the Administration Server to APPHOST2 if APPHOST1 fails:

1. Configure vip0 on APPHOST2.
2. Start Node Manager NMa on APPHOST2 from the domain directory in shared storage.
3. Start the Administration Server on APPHOST2 using NMa.
4. Start the Administration Console to verify that the Administration Server is running.

Failing Back the Administration Server to the Original Host

You fail back the Administration Server to its original host after it restarts.

To fail back the Administration Server to APPHOST1 when APPHOST1 comes back online:

1. Stop the Administration Server on APPHOST2 using Node Manager NMa.
2. Remove vip0 from APPHOST2.
3. Stop Node Manager NMa on APPHOST2.
4. Configure vip0 on APPHOST1.
5. Start Node Manager NMa on APPHOST1 using the domain directory in shared storage.
6. Use Node Manager NMa to start the Administration Server on APPHOST1.
7. Start the Administration Console to verify that the Administration Server is running.