[awithrow]

I think the only times it ever really makes sense to use logs to generate metrics are fairly limited:

1. You haven't yet instrumented the application with metrics yet.

2. The logs are from a third party tool that don't emit metrics

3. The log format is well defined and doesn't change (I'd still prefer native metrics)

Otherwise the issue is that logging messages can and do change over the lifetime of an application. Relying on the content of the log for metrics becomes an implicit API that's not obvious to developers working on the code. I've seen issues of broken monitoring and alerting because a refactor changed log formatting and content. Much better to be explicit about metrics and instrument them directly.