Thanos is an open-source project that provides highly available Prometheus setup with long-term storage capabilities. It is designed to scale out Prometheus by providing a global query view, deduplication, and downsampling. One of its components, the Thanos Ruler, is responsible for evaluating Prometheus alerting rules against historical data.
When using Thanos, you might encounter the error message: ruler: failed to evaluate alert. This indicates that the Thanos Ruler has encountered an issue while attempting to evaluate an alerting rule. This can disrupt the alerting mechanism, potentially leading to missed alerts or incorrect alert statuses.
The error ruler: failed to evaluate alert typically arises due to syntax errors in the alerting rules or missing data required for evaluation. Thanos Ruler relies on correctly formatted Prometheus alerting rules to function properly. If there are any discrepancies in the syntax or if the data required for evaluation is unavailable, this error may occur.
Ensure that all alerting rules are correctly formatted. You can use the Prometheus alerting rules documentation to verify the syntax. Additionally, tools like Promtool can be used to validate the rules:
promtool check rules /path/to/your/rules/file
Ensure that the data required for the alert evaluation is available and accessible. You can query the data directly using Prometheus or Thanos Query to verify its presence:
thanos query --query="up{job='your_job_name'}"
Check the configuration of Thanos Ruler to ensure it is correctly set up to evaluate the rules. Pay attention to the rule file paths and any external data sources configured.
Examine the logs of the Thanos Ruler component for any additional error messages or warnings that might provide more context about the issue. Logs can often reveal configuration issues or data access problems.
By following these steps, you should be able to diagnose and resolve the ruler: failed to evaluate alert error in Thanos. Ensuring proper syntax, data availability, and configuration will help maintain a robust alerting system. For further reading, consider exploring the Thanos Ruler documentation.
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