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Automatic logging: Trace discovery through logs

Running instrumented distributed systems is a very powerful way to gain understanding over a system, but it brings its own challenges. One of them is discovering which traces exist.

In the beginning of Tempo, querying for a trace was only possible if you knew the ID of the trace you were looking for. One solution was automatic logging. Automatic logging provides an easy and fast way of discovering trace IDs through log messages. Well-formatted log lines are written to a Loki instance or to stdout for each span, root, or process that passes through the tracing pipeline. This allows for automatically building a mechanism for trace discovery. On top of that, we also get metrics from traces using Loki, and allow quickly jumping from a log message to the trace view in Grafana.

While this approach is useful, it isn’t as powerful as TraceQL. If you are here because you know you want to log the trace ID, to enable jumping from logs to traces, then read on!

If you want to query the system directly, read the TraceQL documentation. We doubt you’ll be sad.

Configuration

For high throughput systems, logging for every span may generate too much volume. In such cases, logging per root span or process is recommended.

Automatic logging overview

Automatic logging searches for a given set of attributes in the spans and logs them as key-value pairs. This allows searching by those key-value pairs in Loki.

Before you begin

To configure automatic logging, you need to select your preferred backend and the trace data to log.

To see all the available config options, refer to the configuration reference.

This simple example logs trace roots to stdout and is a good way to get started using automatic logging:

yaml
traces:
  configs:
  - name: default
    ...
    automatic_logging:
      backend: stdout
      roots: true

This example pushes logs directly to a Loki instance also configured in the same Grafana Agent.

yaml
traces:
  configs:
  - name: default
    ...
    automatic_logging:
      backend: logs_instance
      logs_instance_name: default
      roots: true

Examples

Automatic logging overview

Automatic logging overview