Prometheus is an open-source systems monitoring and alerting toolkit originally built at SoundCloud. It is designed to record real-time metrics in a time-series database, built using a highly dimensional data model. Prometheus is widely used for monitoring and alerting due to its powerful query language, PromQL, and its ability to handle high-dimensional data.
One common issue users encounter is that Prometheus stops scraping targets after a restart. This can be observed when the Prometheus dashboard shows no new data being collected, or when alerts are triggered due to missing metrics.
When Prometheus is not scraping after a restart, it often indicates that the configuration has not been reloaded correctly, or there are network connectivity issues. Prometheus requires a valid configuration file to know which targets to scrape and how to do so. If this configuration is not loaded properly, Prometheus will not function as expected.
Prometheus relies on a YAML configuration file to define its scraping targets and rules. If this file is not reloaded after changes, Prometheus will continue using the old configuration.
Network issues can prevent Prometheus from reaching its targets. This could be due to firewall settings, DNS resolution problems, or incorrect target URLs.
Ensure that your Prometheus configuration file is correct and has been reloaded. You can check the configuration by running:
promtool check config /path/to/prometheus.yml
If there are errors, correct them and reload the configuration using:
kill -HUP $(pgrep prometheus)
Alternatively, if you are using a service manager like systemd, you can restart the service:
sudo systemctl restart prometheus
Ensure that Prometheus can reach its targets. You can test connectivity using tools like ping or curl:
ping target-hostnamecurl http://target-hostname:port/metrics
If there are connectivity issues, check your firewall settings and DNS configuration.
Check Prometheus logs for any errors or warnings that might indicate the cause of the issue. Logs can be found in the default logging location or specified in the Prometheus configuration:
tail -f /var/log/prometheus/prometheus.log
For more detailed information on configuring and troubleshooting Prometheus, you can refer to the official Prometheus Documentation. Additionally, the Configuration Guide provides insights into setting up and managing your Prometheus instance.
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