Add alert rules

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Support for providing alert rules through the relation is available for loki-k8s and prometheus-k8s, both directly and through intermediary charms like grafana-agent-k8s and prometheus-scrape-config-k8s.

Prerequisites

To be able to pass on alert rules, you also need to implement their corresponding telemetry relation interface, as well as instantiating their corresponding library classes. For Prometheus, the relation interface is either prometheus_scrape and MetricsEndpointProvider, or prometheus_remote_write and RemoteWriteConsumer. For Loki, this is loki_push_api and either LokiPushApiConsumer or LogProxyConsumer. If both interfaces are implemented, it would roughly look as follows:

provides:
  metrics-endpoint:
    interface: prometheus_scrape

requires:
  logging:
    interface: loki_push_api

Create an alert rule

An alert rule consists of a name, an expression, a duration, as well as optionally a set of labels and annotations. In this how to, we’ll use an alert rule for zinc-k8s. For the sake of this how to, the details of the rule are of less importance. If you want to learn more about crafting alert rules, have a look at the official Prometheus or Loki documentation.

alert: ZincTargetMissing
expr: up == 0
for: 0m
labels:
  severity: critical
annotations:
  summary: Prometheus target missing (instance {{ $labels.instance }})
  description: |
    A Prometheus target has disappeared. An exporter might be crashed.
    VALUE = {{ $value }}\n LABELS = {{ $labels }}

Save the file in ./src/prometheus_alert_rules for Prometheus, or ./src/loki_alert_rules for Loki, using a file name ending with .rule. Next time you pack and deploy your charm, the alert rules will be transferred over as you integrate it with something using a supported relation interface.

Note: Custom paths must be passed as an argument to the constructor (e.g. alert_rules_path=./src/rules/loki).

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