Enable global file logging

[Mpdreamz]

This ensures we can specify file logging globally and uniformly. Greatly simplifying the debug-ability of the agent.

The preferred way is to set any or all of the following:

• ELASTIC_OTEL_LOG_TARGETS (to anything but none)
  • if only set to stdout no file will be created but global logging will kicking )
• OTEL_DOTNET_AUTO_LOG_DIRECTORY
• OTEL_LOG_LEVEL
  • trace debug will enable global file logging if the other two variables are not set explicitly.

This ensure we have one way to debug both our proprietary agent as well as the Elastic OpenTelemetry Distribution.

See: https://github.com/elastic/elastic-otel-dotnet/pull/129

For backwards compatible reasons the profiler variables are also supported:

• ELASTIC_APM_PROFILER_LOG
• ELASTIC_APM_PROFILER_LOG_DIR
• ELASTIC_APM_PROFILER_LOG_TARGETS

Globally setting

• ELASTIC_APM_LOG_LEVEL and ELASTIC_APM_LOG_DIRECTORY is also supported but not preferred.

Setting these in any of our supported deploy scenarios:

• Manual instrumentation (nuget)
  • ASP.NET (classic)
  • ASP.NET core
  • NOTE: we now log to both the configured ILogger and our global logging.
• Auto Instrumentation
  • Profiler
  • Startup hooks To keep support existing deploys this now always globally logs to file if only ELASTIC_APM_STARTUP_HOOKS_LOGGING is set as well.

This further updates our docs for the profiler and troubleshooting to prefer ELASTIC_OTEL_* variables.

The profiler is updated to read the same environment variables as managed code.

[Mpdreamz]

A couple of minor fix suggestions. The only thing I'm a little unsure about is using the ELASTIC_OTEL_ env vars for this agent. I like that migration is easier, but not sure if it's subtly confusing why OTEL is mentioned in their names.

Aye, it's not ideal but I'd love to be in a situation where we can point customers to 3 variables that work across the board and in mixed environments.

We could use:

• ELASTIC_APM_LOG_LEVEL
• ELASTIC_APM_LOG_DIRECTORY
• ELASTIC_APM_LOG_TARGETS

For both? Or:

• ELASTIC_APM_FILE_LOG_LEVEL
• ELASTIC_APM_FILE_LOG_DIRECTORY
• ELASTIC_APM_LOG_TARGETS

[stevejgordon]

Yeah, okay. If we want one set to work for all things, let's go with the OTEL-based names, as that's where we expect to end up eventually. Would these make sense, since log level can apply to other loggers that may not be file-based?

• ELASTIC_OTEL_LOG_LEVEL
• ELASTIC_OTEL_FILE_LOG_DIRECTORY
• ELASTIC_OTEL_LOG_TARGETS

[Mpdreamz]

Yeah it might make sense ELASTIC_OTEL_FILE_LOG_LEVEL on its own is enough to start logging to file today.

ELASTIC_OTEL_LOG_LEVEL on its own might be slightly confusing because the default for ELASTIC_OTEL_LOG_TARGETS is to include file.

However I think its benefits negate the possible confusion.

If we take this further we can also rename ELASTIC_OTEL_FILE_LOG_DIRECTORY to ELASTIC_OTEL_LOG_DIRECTORY since this only makes sense to file logging anyhow.

I'll update the PR to the following set:

• ELASTIC_OTEL_LOG_LEVEL
• ELASTIC_OTEL_LOG_DIRECTORY
• ELASTIC_OTEL_LOG_TARGETS

I like symmetry in the naming and its more terser 😸