Hello Dan,
> -Ursprüngliche Nachricht-
> Von: Dan McLaughlin
> Gesendet: Freitag, 16. Juni 2023 18:54
> An: Tomcat Users List
> Betreff: Words of Wisdom re: Context Versioning - Parallel Deployment
>
> Does anyone have any advice on implementing Context Versioning (parallel
> deployment) in Tomcat? It seems to have been a feature for quite some
> time.
> Is it stable? What are the typical issues people run into? JMX issues?
> Classloader issues?
>
> I've tried to do a parallel deployment with our applications as they exist
> today, and I can already see a few problems we'd have to address.
>
> 1) We have a concept of a workdir where we will extract configuration-
> related properties files, XML, etc... on initial start-up; the workdir also
> contains working files related to things like XA transaction logs and
> application-specific logging. We'd probably need to append the context
> version to our workdir path so that each version can have separate
> application logs, configuration settings, etc...
>
> 2) We use JMX MBeans throughout our apps to allow real-time configuration
> of our applications. Since our apps weren't originally developed with parallel
> deployment in mind, so a parallel deployment results in two app versions
> trying to use the same JMX MBeans. I can see in our app logs when I try to
> deploy two versions, the second version will either throw an exception and
> fail to start because the MBean exists, or it will try to destroy and recreate
> the MBean--which could cause issues if it changes a setting that the first
> version of the app depended on. I assume we will need to fix all our code to
> somehow version the MBeans so there aren't conflicts.
>
> 3) Do third-party dependencies that use JMX pose any issues? We use jgroups
> and log4j2. Both create their own mbeans, but it seems we have control over
> the names they use.
>
> Do you know if there are any other issues we need to consider? Words of
> wisdom?
>
> Thanks!
>
> Dan
>
Just some thoughts / ideas from my side:
a) If you use any scheduler (e.g. quartz) you must use a DB based
synchronization / clustering
b) When using caches, they must be synchronized between the two apps
c) Some frameworks have built-in caches which must be taken into account (e.g.
eclipse link)
d) Any shared resources should be checked whether parallel access might cause
problems
e) Opening listening ports might conflict
I would like to try this feature in future. The above mentioned are some
thoughts I made up to now.
Greetings,
Thomas
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