What are Alertmanager rules in Prometheus?

What are Alertmanager rules in Prometheus?

Alertmanager rules are configurations that define how alerts are handled in Prometheus. They specify conditions for triggering alerts and how to group, route, and silence them.

How do I create a new alert rule?

To create a new alert rule, you need to define it in a YAML file under the 'rules' section, specifying the alert name, conditions, and labels.

Can you give me an example of an alert rule?

Sure! Here's a simple example:

- alert: HighCPUUsage
  expr: sum(rate(cpu_usage[5m])) by (instance) > 0.9
  for: 5m
  labels:
    severity: critical
  annotations:
    summary: "High CPU usage detected on {{ $labels.instance }}"

This rule triggers an alert if CPU usage exceeds 90% for 5 minutes.

What happens when an alert is triggered?

When an alert is triggered, Alertmanager processes it according to the defined routing rules, sending notifications to the specified channels like email, Slack, or PagerDuty.