Add option for logback to capture message template

[philsttr]

Partially implements #15119. Only for logback.

Added a new captureTemplate option to the logback OpenTelemetryAppender. Default is false.
The new option captures the unformatted log message template in the log.body.template log event attribute proposed in open-telemetry/semantic-conventions#1283.

For example:

logger.info("My favorite color is: {}", favoriteColor);

will result in the log.body.template attribute being set to My favorite color is: {}

Enable in the library by configuring the OpenTelemetryAppender with <captureTemplate>true</captureTemplate>.
Enable in the javaagent by setting otel.instrumentation.logback-appender.experimental.capture-template=true.

The existing captureArguments option previously enabled both capturing the template and arguments. However, it was only documented to capture the arguments. Now captureArguments only enables capturing arguments (not the message template). This is a backwards incompatible change to an experimental config option. Users currently setting captureArguments=true would now need to set both captureArguments=true and captureTemplate=true to maintain the previous behavior.

This PR only implements this change for logback (not log4j, jboss-logmanager, or java-util-logging). Others could be done in future PRs.

[philsttr]

failing tests seem unrelated to changes in this PR

[zeitlinger]

proposed in open-telemetry/semantic-conventions#1283.

this is an issue - can you create a PR in sem-conv?

[philsttr]

Hallo @zeitlinger

To clarify, the logback instrumentation already populates the log.body.template attribute (and the log.body.parameters attribute). This PR changes the configuration option that controls when the log.body.template attribute gets populated.

I can submit a PR for http://github.com/open-telemetry/semantic-conventions/issues/1283, but I feel that is a separate, but related, issue. In other words, I don't think this PR should depend on the new sem-conv PR, since the attributes are currently in use.

[zeitlinger]

I don't think this PR should depend on the new sem-conv PR, since the attributes are currently in use.

agreed

[philsttr]

When captureTemplate=true, I'm debating whether the log.body.template should
A) be captured even if no arguments are provided (meaning the message is not really a template, but the full message)
OR
B) only be captured if arguments are provided (thus, indicating that the message is actually a template)

Currently, the PR implements A, but I think I'm leaning toward B now, to reduce log volume.

If I change the implementation to B, then captureTemplate=true + captureArguments=true is essentially the same as the existing captureArguments=true behavior.

Anybody have any thoughts?

[cyrille-leclerc]

Capturing the logline template & arguments, even when no argument is used, provides the great benefit of enabling log analytics tools to immediately provide log trend analytics without having to parse the logline through CPU & memory intensive log pattern extraction algorithms.

I'm not aware of existing log analytics solution that today leverages log.body.template and log.record.parameters but it's very compelling and should be straightforward to support in log trend analytics.

[philsttr]

Capturing the logline template & arguments, even when no argument is used, provides the great benefit of enabling log analytics tools to immediately provide log trend analytics without having to parse the logline through CPU & memory intensive log pattern extraction algorithms.

I think this can be done with both option A or B that i mentioned earlier. For option B, if a log event has no log.event.parameters and the therefore no log.body.template, then the log analytics tools could look at the log body for that event, since in this case its value would be the same as log.body.template if it were written.

[philsttr]

I've updated the implementation to option B.

This reduces log data volume, makes it easier for users to revert to previous behavior, and still enables usage of the log.body.template by log analyzers when available.