I am new to upgrade process and we are planning to upgrade our application which is built on Pega 7.2.2 to Pega 8.1. App server we are using is IBM WebSphere Application Server v8.5, however in pega platform support guide it is mentioned that this version of App server is not supported by Pega 8.1. My question is - Do we need to upgrade App server first to Websphere v9.0 before upgrading to Pega 8.1. If yes, then won't there be any issue with existing pega 7..2.2 as Wbsphere v9.0 does not support Pega 7.2.2?
If you upgrade both in the same timeframe before you actually use the application, it shouldn't matter. You can wait until both the application server and Pega application are upgraded before starting any nodes. If you need to run with one upgraded for a time before doing the other, I'd suggest starting with the application server in a lower environment to see how it goes.