Configure Tempo for WARN log level in JSON format

[vpmedia]

Hi!

I've my Grafana Tempo instance configured for WARN log level in JSON format, like this:

server:
  log_format: json
  log_level: warn

Still I'm seeing non-json formatted info level logs like this:

tempo-1    | time=2025-10-14T05:35:22.775Z level=INFO source=/home/runner/work/tempo/tempo/vendor/github.com/prometheus/prometheus/tsdb/wlog/watcher.go:523 msg="Done replaying WAL" tenant=single-tenant component=remote remote_name=786027 url=http://host.docker.internal:9090/api/v1/write duration=30.004237669s
tempo-1    | time=2025-10-14T07:34:52.777Z level=INFO source=/home/runner/work/tempo/tempo/vendor/github.com/prometheus/prometheus/tsdb/agent/db.go:647 msg="series GC completed" tenant=single-tenant component=wal duration=1.706356ms
tempo-1    | time=2025-10-14T09:34:52.779Z level=INFO source=/home/runner/work/tempo/tempo/vendor/github.com/prometheus/prometheus/tsdb/agent/db.go:647 msg="series GC completed" tenant=single-tenant component=wal duration=1.3682ms
tempo-1    | time=2025-10-14T11:34:52.782Z level=INFO source=/home/runner/work/tempo/tempo/vendor/github.com/prometheus/prometheus/tsdb/agent/db.go:647 msg="series GC completed" tenant=single-tenant component=wal duration=2.960657ms
tempo-1    | time=2025-10-14T13:34:52.784Z level=INFO source=/home/runner/work/tempo/tempo/vendor/github.com/prometheus/prometheus/tsdb/agent/db.go:647 msg="series GC completed" tenant=single-tenant component=wal duration=1.734456ms

Is there any way to configure the used Prometheus TSDB component to use the root logger configuration?

[joe-elliott]

That may have been a miss when building the generator component. We use logfmt and have never noticed. I believe the appropriate config would need to be passed forward here:

https://github.com/grafana/tempo/blob/main/modules/generator/storage/instance.go#L69C2-L69C8

if you'd like to submit a PR i'd be glad to review.