Code QuizAdvanced

Prometheus Instance-Down Alert Bug

Spot the logic error in a Prometheus alerting rule meant to detect down targets.

Codeyaml

groups:
  - name: instance-health
    rules:
      - alert: InstanceDown
        expr: up == 1
        for: 5m
        labels:
          severity: critical
        annotations:
          summary: "Instance {{ $labels.instance }} is down"
          description: "{{ $labels.instance }} has been unreachable for 5 minutes."

This rule should alert when a scrape target is unreachable, but it never fires for a real outage. What is the bug?

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