A traditional IS cluster, as defined by the documentation, requires some type of shared memory. Some people refer to this is as a stateful cluster. Now, it is also possible to configure multiple load balanced Integration Servers without any shared memory depending on what products you’re using and how. Some people refer to this is a stateless cluster. However, based on your comments thus far, I’m assuming you’re interested in a traditional cluster.
Having said this, then yes, you will need either Coherence and Terracotta. If I recall correctly, 8.2 was the last version to offer Coherence as an option. Since then, the only option is Terracotta. Therefore, we can scratch the idea of using Coherence because it makes no sense for you to setup a Coherence-based cluster now and then have to convert it to Terracotta in your next upgrade.
Terracotta requires additional installation and configuration so one of the first things you will have to do is (1) identify what version of Terracotta you need for your version of IS (http://techcommunity.softwareag.com/ecosystem/documentation/webmethods/wmsuites/Current_webMethods_and_Terracotta_Compatibility_Matrix.pdf) and then (2) download that version of Terracotta from Empower.
Next, you’ll have to install it, which typically involves unzipping a file into a directory of your choice. The basic clustering license allows you to create a simple Terracotta Server Array (TSA) with a pair of active-passive servers, which means you’ll likely be installing Terracotta on two separate servers. Many customers with the typical 2-node cluster choose to simply install Terracotta on the same servers as the IS but you don’t have to do this. Up to you.
Once Terracotta is installed, you now need to configure it. The vast majority of the configuration is done through a file called tc-config.xml.
This page on Empower appears to have some good info for you to follow: https://empower.softwareag.com/sl24sec/SecuredServices/document/java/Troubleshooting/atg/Integration_Server_Terracotta_Cluster_Troubleshooting.html
If you get stuck, let us know.
Percio
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