Creating Alerting Rules

1 hour
  • 3 Learning Objectives

About this Hands-on Lab

After deploying a Prometheus environment to our Kubernetes cluster, the team has decided to test its monitoring capabilities by configuring alerting of our Redis deployment. We have been tasked with writing two alerting rules. The first rule will fire an alert if any of the Redis pods are down for 10 minutes. The second alert will fire if there are no pods available for 1 minute.

Learning Objectives

Successfully complete this lab by achieving the following learning objectives:

Create a ConfigMap That Will Be Used to Manage the Alerting Rules

Edit prometheus-rules-config-map.yml and add the Redis alerting rules. It should look like this when we’re done:

apiVersion: v1
kind: ConfigMap
metadata:
  creationTimestamp: null
  name: prometheus-rules-conf
  namespace: monitoring
data:
  redis_rules.yml: |
    groups:
    - name: redis_rules
      rules:
      - record: redis:command_call_duration_seconds_count:rate2m
        expr: sum(irate(redis_command_call_duration_seconds_count[2m])) by (cmd, environment)
      - record: redis:total_requests:rate2m
        expr: rate(redis_commands_processed_total[2m])
  redis_alerts.yml: |
    groups:
    - name: redis_alerts
      rules:
      - alert: RedisServerDown
        expr: redis_up{app="media-redis"} == 0
        for: 10m
        labels:
          severity: critical
        annotations:
          summary: Redis Server {{ $labels.instance }} is down!
      - alert: RedisServerGone
        expr:  absent(redis_up{app="media-redis"})
        for: 1m
        labels:
          severity: critical
        annotations:
          summary: No Redis servers are reporting!
Apply the Changes Made to `prometheus-rules-config-map.yml`

Now, apply the changes that were made to prometheus-rules-config-map.yml:

kubectl apply -f prometheus-rules-config-map.yml
Delete the Prometheus Pod
  1. List the pods to find the name of the Prometheus pod:

    kubectl get pods -n monitoring
  2. Delete the Prometheus pod:

    kubectl delete pods <POD_NAME> -n monitoring
  3. In a new browser tab, navigate to the Expression browser:

    http://<IP>:8080
  4. Click on the Alerts link to verify that the two Redis alerts are showing as green.

Additional Resources

  1. Use prometheus-rules-config-map.yml to create a configuration map for the Redis alerting rules:

    • The file is located in /root/prometheus.
    • Under the data section, add a new file called redis-alerts.yml.
    • Create an alerting group called redis_alerts.
    • This group will contain two rules: RedisServerGone and RedisServerDown.
  2. The RedisServerDown alert:

    • The expression uses the redis_up metric and is filtered using the label app with media-redis as the value. The condition will equal 0.
    • The alert will fire if the condition remains true for 10 minutes.
    • The alert has a severity of critical.
    • Add a summary in annotations that says “Redis Server <SERVER_NAME> is down!”
    • Replace <SERVER_NAME> with the templating syntax that displays the instance label.
  3. The RedisServerGone alert:

    • For the expression, use the absent function to evaluate the redis_up metric. Filter using the app label with a value of media-redis.
    • The alert will fire if the condition remains true for 1 minute.
    • The alert has a severity of critical.
    • Add a summary in annotations that says “No Redis servers are reporting!”
  4. Apply the changes made in prometheus-rules-config-map.yml.

    • Make sure the rules propagate into Prometheus.
    • Delete the Prometheus pod to make the rules propagate.
    • Verify the rules are showing up by clicking on Alerts.
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