when upgrading Siteminder to the newest release (e.g. while performing a migration) we usually suggest the following migration order:
migrate one policy server, migrate one web agent, migrate all the other policy server and webagent, migrate the policy store and finally migrate the Admin UI.
One of my customer is migrating from the release r12.0 SP3 CR11 to the release r12.52 SP2 Cr1 and they would like to defer the webagent migration , and complete all the other steps in advance (migrate policy server, then migrate policy store and then migrate admin ui) leaving webagent at old release
What are the pros/cons of migrating all the component except the web agents?
Migrating web agents at the last is perfectly fine. As you might know, policy servers are always backward compatible with web agents.
So you can configure r12.52 policy server with any prior version of web agents e.g r12.51,r12.5,12.0,6.x etc.
Yes as Ujwol mentioned policy servers are always backward compatible with web agents. However, just make sure under the support matrix that the web agents are not too old versions which may not be compatible with latest version of Policy server.
Moreover, it would be good to inform the web servers (webagent owner /application owner) about the policy server upgrade so as if any issues are observed at webagent level related to compatibility or any other unseen issues they would be able to report the policy server owner immediately.
In my previous experience, we did migration for the policy servers and other related stuff, however we only upgrade those webagents who were no longer supported with the upgrade version of Policy servers or those webagents which faced issues.
I've always thought he best, safest approach is to parallel with building the foundation (prerequisites: your Stores, Java etc) of the policy server, then the Policy Server (with WAM UI) and finally going and finding your agents in use and switching those over. there's a scrip on these forums that can do that rather welll... well 2...
Finding Agent Versions