Sun Cluster Data Service for Apache Tomcat Guide for Solaris OS

Planning the Sun Cluster HA for Apache Tomcat Installation and Configuration

This section contains the information you need to plan your Sun Cluster HA for Apache Tomcat installation and configuration.

About Horizontal Scalability

Sun Cluster includes a concept of horizontal scalability for data services called scalable service. Ip based load-balancing algorithms are integrated in this concept. Because of this reason you can scale horizontally without using hardware loadbalancers. For a more detailed discussion of this scalable service see Sun Cluster Concepts Guide for Solaris OS.

Before using the Sun Cluster HA for Apache Tomcat in a scalable configuration, it is necessary to have a closer look at the infrastructure of the cluster and the clients.

If your clients access your application using proxies, determine whether the used proxy stays the same during a session context. This is true for an intranet.

If the proxy changes during a session context it means, from the load-balancing point of view, that the source ip address is changing. This will spoil every ip based load-balancing, wether it is hardware or software.

Especially when your client accesses the server over the Internet, it is not guaranteed, that the source ip address remains the same during a session context.

Sun Cluster HA for Apache Tomcat can be configured two ways to get horizontal scalability.

Using Sun Cluster HA for Apache Tomcat in a purely scalable configuration.
Using Sun Cluster HA for Apache Tomcat in a multiple masters configuration.

The difference between the two configuration is in the way of accessing the nodes.

A client accesses the scalable configuration by its shared address. In this case, Sun Cluster does the load-balancing.
A client accesses a multiple masters configuration using each node's physical address. Load-balancing must be done outside of the cluster.

For more information about scalable data services, see Sun Cluster Concepts Guide for Solaris OS.

Both configuration options are discussed in the sectionsSun Cluster HA for Apache Tomcat as a scalable configuration and Sun Cluster HA for Apache Tomcat as a multiple master configuration.

Sun Cluster HA for Apache Tomcat as a scalable configuration

You can use Sun Cluster HA for Apache Tomcat in a scalable configuration if it is guaranteed, that the source ip address remains the same during a session context. This guarantee is achieved in example in an intranet.

If the source ip address might change during a session context and a scalable configuration is required, Apache Tomcat needs to be configured with session replication. This can be done by the application using a global file system or a database.

Caution –

You will get a performance penalty from this approach.

You will get better performance using Tomcats inbound memory session replication for a scalable configuration with changing source ip addresses.

You can achieve the session replication for Apache Tomcat 4.x by following the instructions at http://www.theserverside.com/resources/article.jsp?l=Tomcat.
For Apache Tomcat 5.x, inbound memory session replication as a built-in feature, is on the feature list.
For Apache Tomcat 3.x the inbound memory session replication is not configurable.

Sun Cluster HA for Apache Tomcat as a multiple master configuration

You can use Sun Cluster HA for Apache Tomcat in a multiple master configuration in the other scenarios. External load-balancing is required. A typical configuration uses the scalable Apache web server as a load balancer and configures one physical host name of an Apache Tomcat instance behind each instance of the Apache web server. Another option is to use a hardware load balancer, which handles the session context.

The difference between scalable and multiple masters configuration is only in the way, the clients access the cluster nodes. In a scalable configuration, they access the shared address. Otherwise the clients access the physical hostnames.

Configuration Restrictions

This section provides a list of software and hardware configuration restrictions that apply to Sun Cluster HA for Apache Tomcat only.

For restrictions that apply to all data services, see Sun Cluster Data Services Planning and Administration Guide for Solaris OS.

Deploy a scalable Sun Cluster HA for Apache Tomcat configuration only if either session replication, or reliable source ip addresses are achieved. Otherwise the behavior of the application becomes unpredictable.
Setting the resource parameter Load_balancing_policy to LB_STICKY is strictly required, if Sun Cluster HA for Apache Tomcat is deployed in a scalable configuration with reliable source ip addresses when no session replication is configured. Otherwise, the behavior of the application becomes unpredictable. In every other scalable configuration the Sticky Load_balancing_policy helps to get the more cache hits out of your caches.

Caution –

Your data service configuration might not be supported if you do not observe these restrictions.

Configuration Requirements

These requirements apply to Sun Cluster HA for Apache Tomcat only. You must meet these requirements before you proceed with your Sun Cluster HA for Apache Tomcat installation and configuration.

Caution –

Your data service configuration might not be supported if you do not adhere to these requirements.

Location of the Tomcat Home Directory for Scalable or Multiple Masters Configurations

If you intend to install Apache Tomcat in a scalable resource group, create the Tomcat Home directory and its dynamic data on local storage.

This required because Apache Tomcat uses the directory structure to store its configuration, logs, deployed applications and so on.

If your local storage is not big enough, you can use a Global File System on the shared storage.

Caution –

In this scenario, the deployment of Tomcat applications needs to occur on every node where Apache Tomcat is hosted.

Load Balancing for Multiple Master Configurations

If you intend to install Apache Tomcat in a multiple master configuration, an external load balancer is required.

Location of the Tomcat Home Directory for Failover Configurations

If you intend to install Apache Tomcat in a failover resource group, create the Tomcat Home directory on the shared storage. The location for the Tomcat Home directory can reside on a Global File System (GFS) or it can reside on a Failover File System (FFS) with an HAStoragePlus resource. It is best practice to store it on a FFS.

This is required because Apache Tomcat uses the directory structure to store its configuration, logs, deployed applications, and so on. It is not recommended to store the binaries local and the dynamic parts of the data on the shared storage.

Note –

It is best practice to mount Global File Systems with the /global prefix and to mount Failover File Systems with the /local prefix.

Apache Tomcat Component Dependencies

You can configure the Sun Cluster HA for Apache Tomcat data service to protect one or more Apache Tomcat instances. Each instance needs to be covered by one Apache Tomcat resource. The dependencies between the Apache Tomcat resource and other needed resources are described in Table 3, in Table 4, or in Table 5.

Table 3 Dependencies Failover


Component	Description
Storage Resource	This resource can be a `SUNW.HAStoragePlus` or a `SUNW.HAStorage` resource type.
Apache Tomcat`(Mandatory)`	-> `SUNW.HAStoragePlus` resource or `SUNW.HAStorage` resource The Storage resource manages the Apache Tomcat File System Mount points and ensures that Apache Tomcat is not started until they are mounted.
Logical Host`(Mandatory)`	The Apache Tomcat has an implicit dependency on the logical hosts of the resource group, because it is based on the generic data service. On behalf of this reason a logical Host needs to exist, but no explicit dependency is necessary.

Because of the special requirements of a scalable configuration, you need no dependencies to storage or addresses, as long as every Apache Tomcat and its parameter file pfile is stored on the root file system. Otherwise follow Table 4.

Table 4 Dependencies Scalable


Component	Description
Storage Resource	This resource can be a `SUNW.HAStorage` or a `SUNW.HAStoragePlus` resource type.
Apache Tomcat`(Mandatory)`	-> Storage resource The Storage resource manages the Apache Tomcat File System Mount points and ensures that Apache Tomcat is not started until they are mounted.
Shared address`(Mandatory)`	The shared address resource resides in a separate resource group on which the scalable resource group depends.

A multiple master configuration is running on more than one nodes like a scalable configuration, but without a shared address. Because of the special requirements of a multiple masters configuration, you need no dependencies to storage or addresses, as long as every Apache Tomcat and its parameter file pfile is stored on the root file system. Otherwise follow Table 5.

Table 5 Dependencies Multiple Masters


Component	Description
Storage Resource	This resource can be a `SUNW.HAStorage` or a `SUNW.HAStoragePlus` resource type.
Apache Tomcat`(Mandatory)`	-> Storage resource The Storage resource manages the Apache Tomcat File System Mount points and ensures that Apache Tomcat is not started until they are mounted.
Shared address`(Mandatory)`	The shared address resource resides in a separate resource group on which the scalable resource group depends.

Note –

For more detailed information about Apache Tomcat, refer to the http://jakarta.apache.org web page.

Apache Tomcat Configuration and Registration Files

Apache Tomcat component has configuration and registration files in the directory /opt/SUNWsctomcat/util . These files let you register the Apache Tomcat component with Sun Cluster.

Within these files, the appropriate dependencies have been applied.

# cd /opt/SUNWsctomcat
# 
# ls -l util
total 4
-rwx--x---   1 root     other        709 Apr 29 11:57 sctomcat_config
-rwx--x---   1 root     other        561 Apr 29 11:58 sctomcat_register
# more util/*g
::::::::::::::
util/sctomcat_config
::::::::::::::
#
# Copyright 2003 Sun Microsystems, Inc.  All rights reserved.
# Use is subject to license terms.
# 
# This file will be sourced in by sctomcat_register and the parameters
# listed below will be used.
#
# These parameters can be customized in (key=value) form
#
#        RS - name of the resource for the application
#        RG - name of the resource group containing RS
#      PORT - name of the port number
#        LH - name of the LogicalHostname SC resource
#  SCALABLE - true or false for a scalable or failover resource
#   NETWORK - false or true, false for multiple master configurations without
#             shared address, in this case SCALABLE will be ignored
#
#     PFILE - absolute pathname to the parameter file for the Tomcat resource
#    HAS_RS - name of the HAStoragePlus SC resource 
#             (it can be a , separated list for the dependencies)
#

RS=
RG=
PORT=8080
LH=
SCALABLE=false
NETWORK=true
PFILE=
HAS_RS=