What are the differences between Prometheus Recording Rules and Alerting Rules?

Differences and usage of Prometheus Recording Rules and Alerting Rules:

Recording Rules:

• Pre-calculate and store common query results
• Improve query performance and reduce computational overhead
• Do not trigger alerts

Configuration Example:

yaml
groups:
  - name: api_recording_rules
    interval: 30s
    rules:
      - record: job:http_requests:rate5m
        expr: sum by (job) (rate(http_requests_total[5m]))
      
      - record: job:request_errors:rate5m
        expr: sum by (job) (rate(http_requests_total{status=~"5.."}[5m]))

Use Cases:

• Frequently queried complex expressions
• Calculations that aggregate multiple metrics
• Improve dashboard loading speed
• Reduce real-time query pressure

Alerting Rules:

• Monitor metrics and trigger alerts
• Support alert grouping, inhibition, and silencing
• Send notifications to Alertmanager

Configuration Example:

yaml
groups:
  - name: api_alerting_rules
    rules:
      - alert: HighErrorRate
        expr: job:request_errors:rate5m / job:http_requests:rate5m > 0.05
        for: 5m
        labels:
          severity: critical
        annotations:
          summary: "High error rate on {{ $labels.job }}"
          description: "Error rate is {{ $value | humanizePercentage }}"

Key Differences:

Feature	Recording Rules	Alerting Rules
Purpose	Pre-calculate query results	Trigger alert notifications
Storage	Generate new time series	Do not store new series
Performance	Improve query performance	May increase evaluation overhead
Usage	Dashboards, queries	Monitoring, alerting

Best Practices:

1. Recording Rules:

   • Use meaningful naming conventions
   • Set reasonable evaluation intervals
   • Regularly review and clean up unused rules
   • Use by clause for grouping

2. Alerting Rules:

   • Set reasonable for parameters to avoid false positives
   • Use tiered alerts (info, warning, critical)
   • Add clear description information
   • Use labels for grouping and routing

3. Rule Management:

   • Use version control for rule files
   • Use promtool to check rule syntax
   • Test rules before deployment
   • Monitor rule evaluation performance

Validate Rules:

bash
promtool check rules /path/to/rules.yml