Provide OpenTelemetry instance to Log4j2 appender after initialization

[rickardoberg]

Describe the bug

The Log4j2 appender seems to have conflicting implementation ideas. On the one hand there is the notion that Log4j2 can be initialized first, and so there is an eventsToReplay queue to deal with this. On the other hand the builder sets the OpenTelemetry instance to the noop version if none is specified, which then effectively throws away the log messages before the real OT instance has been installed, and the eventsToReplay queue never comes into play.

In my case Log4j2 is configured first, and then the OT instance, and so the idea with eventsToReplay would work great, except it's bypassed by the setting of a noop instance, and so I just lose all the log events before the OT instance is installed.

Steps to reproduce

Initialize Log4j2 first, then OT and call install.

Expected behavior

The appender should queue events before install is called (with either noop or SDK instance) and then replay them on install.

Actual behavior

Any events before install will be lost

Javaagent or library instrumentation version

1.32.0-alpha

Environment

JDK:
JDK 17
OS:
Win11

Additional context

No response

[laurit]

@jeanbisutti could you take a look