What is the Prometheus Alert Lifecycle?

The Prometheus alert lifecycle describes the process alerts follow from creation to resolution, enabling effective monitoring and timely notifications. Prometheus generates alerts based on pre-defined rules, which are then processed and managed by systems like Alertmanager.

Stages of the Alert Lifecycle

1. Define Alert Rules
   Alerts are created using alerting rules in prometheus.yml or external rule files. Each rule specifies conditions to trigger an alert using PromQL.
   Example:
   yaml - alert: InstanceDown expr: up == 0 for: 5m labels: severity: critical annotations: summary: "Instance {{ $labels.instance }} is down" description: "No response from {{ $labels.instance }} for 5 minutes"

2. Alert Evaluation
   Prometheus evaluates alerting rules at its scrape interval. If the rule condition is true, the alert enters a pending state but remains silent during this phase.

3. Firing Alerts
   When the condition persists for the specified for duration, the alert transitions to a firing state. Prometheus then sends the alert to Alertmanager, including metadata (e.g., labels and annotations).

4. Routing and Notification
   Alertmanager routes alerts based on defined rules, determining the recipients and notification channels (e.g., email, Slack, PagerDuty).
   Example configuration:
   yaml route: group_by: ['alertname', 'severity'] receiver: 'slack' receivers: - name: 'slack' slack_configs: - channel: '#alerts' text: "{{ .CommonAnnotations.summary }}"

5. Resolution
   Once the alert condition is no longer true, Prometheus marks the alert as resolved and informs Alertmanager, which may notify users about the resolution.

Lifecycle Summary

1. Define Rule →
   
2. Evaluate Condition →
   
3. Pending Alert →
   
4. Firing Alert →
   
5. Alertmanager Processing →
   
6. Notification →
   
7. Resolution

Key Details

• Pending State: Alerts stay in this state until the for duration is met. No notifications are sent during this phase.
• Firing State: The alert is actively sent to Alertmanager for processing and notification.
• Resolved State: Alerts are marked resolved when the condition becomes false, and updates are sent to Alertmanager.
• Expiration: Resolved alerts that no longer match active rules are eventually purged from Prometheus.

Understanding and managing the alert lifecycle ensures that Prometheus monitoring is both reliable and actionable.

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