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Defining recording rules

Configuring rules

Prometheus supports two types of rules which may be configured and then evaluated at regular intervals: recording rules and alerting rules. To include rules in Prometheus, create a file containing the necessary rule statements and have Prometheus load the file via the rule_files field in the Prometheus configuration.

The rule files can be reloaded at runtime by sending SIGHUP to the Prometheus process. The changes are only applied if all rule files are well-formatted.

Syntax-checking rules

To quickly check whether a rule file is syntactically correct without starting a Prometheus server, install and run Prometheus's promtool command-line utility tool:

go get github.com/prometheus/prometheus/cmd/promtool
promtool check-rules /path/to/example.rules

When the file is syntactically valid, the checker prints a textual representation of the parsed rules to standard output and then exits with a 0 return status.

If there are any syntax errors, it prints an error message to standard error and exits with a 1 return status. On invalid input arguments the exit status is 2.

Recording rules

Recording rules allow you to precompute frequently needed or computationally expensive expressions and save their result as a new set of time series. Querying the precomputed result will then often be much faster than executing the original expression every time it is needed. This is especially useful for dashboards, which need to query the same expression repeatedly every time they refresh.

To add a new recording rule, add a line of the following syntax to your rule file:

<new time series name>[{<label overrides>}] = <expression to record>

Some examples:

# Saving the per-job HTTP in-progress request count as a new set of time series:
job:http_inprogress_requests:sum = sum(http_inprogress_requests) by (job)

# Drop or rewrite labels in the result time series:
new_time_series{label_to_change="new_value",label_to_drop=""} = old_time_series

Recording rules are evaluated at the interval specified by the evaluation_interval field in the Prometheus configuration. During each evaluation cycle, the right-hand-side expression of the rule statement is evaluated at the current instant in time and the resulting sample vector is stored as a new set of time series with the current timestamp and a new metric name (and perhaps an overridden set of labels).