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See also the relevant September 2010 Jasig CAS Community Call, with both slides and audio available, which featured a presentation with a perspective on clustering CAS from Howard Gilbert at Yale University.
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Overview
Clustering is essential if your CAS instance is to be "highly available," or HA in manager-speak. Since CAS is a stateful application, there must be a way for each CAS instance to know about what the other CAS instance has done. It would be nice to just use one CAS instance (and one instance on the appropriate hardware can probably easily handle your login needs), but if that instance fails, you do not want all of your users to have to log in again.
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Since CAS stores the login information in the application session we need to setup session replication between our Tomcat instances.
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Note there was an approach (sometimes referenced in older resources) for preserving application login state via a Spring Workflow 1.0 configuration option (Spring 1.0 documentation on this here). Spring Webflow 2.0+ (used in modern versions of CAS) no longer has this feature, meaning this state must be maintained in some other way (such as Tomcat session replication covered here). |
The first thing you need to do is tell CAS (the application) that it is distributable 1. So, in the CAS web.xml file you need to add the <distributable/> tag. The web.xml file is located here:
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