Prometheus is an open-source systems monitoring and alerting toolkit originally built at SoundCloud. It is now a part of the Cloud Native Computing Foundation. Prometheus is designed to collect metrics from configured targets at given intervals, evaluate rule expressions, display the results, and trigger alerts if some condition is observed to be true.
One common issue that users might encounter is Prometheus not scraping metrics from targets due to DNS issues. This can manifest as missing data in your dashboards or alerts not firing as expected. The logs might show errors related to DNS resolution failures.
When Prometheus is unable to scrape metrics, it often logs errors indicating that it cannot resolve the DNS names of the targets. This can be due to several reasons, such as DNS server unavailability, incorrect DNS settings, or network issues preventing DNS queries from reaching the DNS server.
level=error ts=... caller=scrape.go:... msg="Scrape failed" err="Get http://example.com/metrics: dial tcp: lookup example.com: no such host"level=warn ts=... caller=manager.go:... msg="Error refreshing targets" err="lookup example.com on 192.168.1.1:53: no such host"Resolving DNS issues involves a few steps to ensure that the DNS settings are correct and that the DNS server is reachable.
Check the DNS settings on the server where Prometheus is running. Ensure that the DNS server addresses are correctly configured in /etc/resolv.conf or equivalent configuration files.
cat /etc/resolv.conf
Ensure that the DNS servers listed are reachable and correct.
Use tools like dig or nslookup to test DNS resolution for the target addresses.
dig example.com
If the DNS resolution fails, verify the network connectivity to the DNS server and check for any firewall rules that might be blocking DNS queries.
Ensure that the server running Prometheus can reach the DNS server. Use ping or traceroute to diagnose network issues.
ping 192.168.1.1
If there are connectivity issues, investigate network configurations, such as routing tables or firewall settings.
Ensure that the target URLs in the Prometheus configuration file (prometheus.yml) are correct and use valid hostnames.
scrape_configs:
- job_name: 'example'
static_configs:
- targets: ['example.com:9090']
After making changes, reload the Prometheus configuration:
kill -HUP $(pgrep prometheus)
For more detailed information on Prometheus configuration and troubleshooting, refer to the Prometheus Documentation. Additionally, the Configuration Guide provides insights into setting up and managing your Prometheus instance effectively.
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