Proper error message when trying runtime attach with wrong user

[SylvainJuge]

Description

Runtime attach requires to use the same OS user that is running the target JVM.

While this requirement is written in our documentation in the Caveats section, forgetting about this is rewarded with a very cryptic error message similar to:

2020-12-02 17:27:20.717 INFO Attaching the Elastic APM agent to XXXX
Exception in thread "main" java.lang.IllegalStateException: Error during attachment using: co.elastic.apm.attach.bytebuddy.agent.ByteBuddyAgent$AttachmentProvider$Compound@1b9e1916
at co.elastic.apm.attach.bytebuddy.agent.ByteBuddyAgent.install(ByteBuddyAgent.java:613)
at co.elastic.apm.attach.bytebuddy.agent.ByteBuddyAgent.attach(ByteBuddyAgent.java:273)
at co.elastic.apm.attach.ElasticApmAttacher.attach(ElasticApmAttacher.java:170)
at co.elastic.apm.attach.RemoteAttacher.main(RemoteAttacher.java:88)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at co.elastic.apm.attach.bytebuddy.agent.Attacher.install(Attacher.java:106)
at co.elastic.apm.attach.bytebuddy.agent.ByteBuddyAgent.install(ByteBuddyAgent.java:608)
... 3 more
Caused by: com.sun.jna.LastErrorException: [1] Operation not permitted
...

Here the Operation not permitted pushes users to try running this as root or even try to look for rights/permissions issues without success.

Proposal

Detect when target JVM and the JVM used for attaching aren't running with the same user and issue a proper error message on how to solve the issue.

[felixbarny]

We should also investigate if it's feasible to switch the user if the user of the target VM is not matching the user of the attaching VM. Maybe even fork a new JVM that runs with the target VM's user.