[Request] Document required JLink modules for Cryostat to work

[andrewazores]

https://github.com/openjdk/jmc/blob/4c9d9e47bcf13d6c12ddfcdeddb2e90dbe3b691b/core/org.openjdk.jmc.rjmx.common/src/main/java/org/openjdk/jmc/rjmx/common/services/jfr/internal/FlightRecorderServiceFactory.java#L44

https://github.com/openjdk/jmc/blob/4c9d9e47bcf13d6c12ddfcdeddb2e90dbe3b691b/core/org.openjdk.jmc.rjmx.common/src/main/java/org/openjdk/jmc/rjmx/common/services/jfr/internal/FlightRecorderCommunicationHelperV2.java#L103

If the check in the second link fails then it will indeed fall back to trying to use V1, which is incorrect and would lead to the com.sun.management.MissionControl class loading (which will always fail on a modern JDK version - there is no module containing this class anymore as far as I can see).

$ jshell
jshell> javax.management.MBeanServerConnection.class.getModule()
$1 ==> module java.management

jshell> jdk.management.jfr.FlightRecorderMXBean.class.getModule()
$2 ==> module jdk.management.jfr

It looks like these two classes and respective modules might be the ones needed to get JFR V2 detection to work. Maybe adding jdk.management.jfr will help?

Originally posted by @andrewazores in #595 (reply in thread)

[andrewazores]

@Josh-Matsuoka could you take a look at this? From my investigation (linked above) it seems like the real problem here is primarily a JMC bug. For our downstream purposes I think it would be enough for now to simply document what the required modules are, so that users know not to JLink those modules out of their application.

[andrewazores]

See cryostatio/cryostat-core#447

[andrewazores]

See also cryostatio/cryostatio.github.io#196

[andrewazores]

I think between the website issue (our documentation) and the -core issue (really the upstream JMC bug) the work is covered, so I will close this issue as a duplicate.