It's nice to check that your configuration is valid before pushing to production.

Prometheus will gracefully fail to reload if there's a bad configuration, but will fail to start if there isn't one at startup. Thus it's wise to check that the configuration is good before checking it in via continuous integration or similar mechanisms.

To facilitate this, promtool which comes with Prometheus has a check config command. Let's download Prometheus and create an invalid config:

wget https://github.com/prometheus/prometheus/releases/download/v2.5.0/prometheus-2.5.0.linux-amd64.tar.gz tar -xzf prometheus-*.tar.gz cd prometheus-* cat >prometheus.yml <<'EOF' scrape_configs: - job_name: prometehus static_configs: - targets: ['localhost:9090'] EOF

If you now check the configuration, you'll see an error:

./promtool check config prometheus.yml Checking prometheus.yml FAILED: parsing YAML file prometheus.yml: yaml: unmarshal errors: line 3: field static_configs not found in type config.plain

and the exit code will be 1, indicating failure.

If you fix the last two lines to be correctly indented and check the config again it will now pass:

./promtool check config prometheus.yml Checking prometheus.yml SUCCESS: 0 rule files found

and the exit code will be 0.

This sort of feature isn't limited to Prometheus, the Alertmanager's amtool has a similar feature too.

Prometheus configuration got you down? Contact us.