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This guide covers observability for a running kona-node: adjusting log verbosity, filtering log targets, and collecting Prometheus metrics into Grafana dashboards.

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Logging

kona-node provides a -v (or --v) flag as a way to set the “verbosity” level for logs. By default, the verbosity level is set to 3, which is the INFO level. The level ranges from 0 being no logs to 5 which includes trace logs. Log levels are listed below, with each level including the one below it.
  • 5: TRACE - very verbose logs that provide a detailed trace
  • 4: DEBUG - logs meant to print debugging information
  • 3: INFO - informational logs
  • 2: WARN - includes warning and error logs
  • 1: ERROR - only error logs are shown
  • 0: No logs
The default verbosity level is -vvv which is the 3 or INFO level. To set the kona-node to print DEBUG logs or level 4, run the node like so: kona-node node -vvvv.

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Filtering Log Targets

By default, the kona-node initializes its tracing (logging) using the default environment variable filter provided by the tracing_subscriber crate. This uses the value in the RUST_LOG environment variable to set the tracing level for specific targets. Effectively, RUST_LOG allows you to bypass the default log level for the whole node or specific log targets. For example, by prepending RUST_LOG=engine=debug to the kona-node command (or setting that as an environment variable), only INFO logs will be displayed except for the engine log target which will also print DEBUG logs. This comes in handy say for when we would like to debug Kona’s P2P stack, we could prepend RUST_LOG=discv5=debug,libp2p=debug to view debug logs from only discv5 and libp2p targets.

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Metrics

The kona-node can serve Prometheus metrics, which are disabled by default. To turn them on, pass the --metrics.enabled cli flag. Unless otherwise specified with the --metrics.port flag, metrics are exposed on port 9090. To grab a snapshot of the metrics, you can visit 0.0.0.0:9090 or curl the url.
The output should be raw text mapping metrics with their values. Remember, this is just a snapshot of the metrics at that point in time. To record and visualize the metrics, we’ll use Grafana and Prometheus.

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Grafana and Prometheus

Prometheus is a simple service that scrapes metrics at a predefined interval. Grafana then uses Prometheus as a “Data Source” to visualize the collected metrics. The Reth book provides a great overview to setting up Prometheus and Grafana. Visit the Reth docs to follow along. The kona-node comes shipped with a default Grafana dashboard for the kona-node. To import the dashboard to grafana, click the + icon > Import Dashboard > paste the contents of kona’s dashboard in the textbox > Load.