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Open source

(Optional) Grafana Mimir ruler

The ruler is an optional component that evaluates PromQL expressions defined in recording and alerting rules. Each tenant has a set of recording and alerting rules and can group those rules into namespaces.

Architecture of Grafana Mimir’s ruler component

Recording rules

The ruler evaluates the expressions in the recording rules at regular intervals and writes the results back to the ingesters. The ruler has a built-in querier that evaluates the PromQL expressions and a built-in distributor, so that it can write directly to the ingesters. Configuration of the built-in querier and distributor uses their respective configuration parameters:

Alerting rules

The ruler evaluates the expressions in alerting rules at regular intervals and if the result includes any series, the alert becomes active. If an alerting rule has a defined for duration, it enters the PENDING (pending) state. After the alert has been active for the entire for duration, it enters the FIRING (firing) state. The ruler then notifies Alertmanagers of any FIRING (firing) alerts.

Configure the addresses of Alertmanagers with the -ruler.alertmanager-url flag, which supports the DNS service discovery format. For more information about DNS service discovery, refer to Supported discovery modes.


The ruler supports multi-tenancy and horizontal scalability. To achieve horizontal scalability, the ruler shards the execution of rules by rule groups. Ruler replicas form their own hash ring stored in the KV store to divide the work of the executing rules.

To configure the rulers’ hash ring, refer to configuring hash rings.

HTTP configuration API

The ruler HTTP configuration API enables tenants to create, update, and delete rule groups. For a complete list of endpoints and example requests, refer to ruler.


The ruler uses the backend configured via -ruler-storage.backend. The ruler supports the following backends:

Local storage

The local storage backend reads Prometheus recording rules from the local filesystem.

Note: Local storage is a read-only backend that does not support the creation and deletion of rules through the Configuration API.

When all rulers have the same rule files, local storage supports ruler sharding. To facilitate sharding in Kubernetes, mount a Kubernetes ConfigMap into every ruler pod.

The following example shows a local storage definition:


The ruler looks for tenant rules in the /tmp/rules/<TENANT ID> directory. The ruler requires rule files to be in the Prometheus format.