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Memcached Alerting with Prometheus

This tutorial shows you how to configure Prometheus-based alerting for a KubeDB-managed Memcached instance using the memcached-alerts Helm chart.

Before You Begin

• Ensure you have a Kubernetes cluster and that kubectl is configured to communicate with it. If you do not already have a cluster, you can create one using kind.

• Install the KubeDB operator by following the steps here.

• Deploy the database in the demo namespace:

  $ kubectl create ns demo
  namespace/demo created
  

• This tutorial assumes you already have a kube-prometheus-stack running in your cluster, with Prometheus configured so that both serviceMonitorSelector and ruleSelector match the label release: prometheus. See the Grafana Dashboard guide for how to deploy kube-prometheus-stack if you don’t have it yet.

  To verify the selectors:

  $ kubectl get prometheus -n monitoring -o jsonpath='{.items[0].spec.ruleSelector}'
  {"matchLabels":{"release":"prometheus"}}
  
  $ kubectl get prometheus -n monitoring -o jsonpath='{.items[0].spec.serviceMonitorSelector}'
  {"matchLabels":{"release":"prometheus"}}
  

• To learn more about how Prometheus monitoring works with KubeDB, see the overview here.

• For dashboards and visualisation, see Grafana Dashboard for Memcached.

Note: YAML files used in this tutorial are stored in docs/examples/memcached folder in GitHub repository kubedb/docs.

Overview

• KubeDB deploys Memcached with a built-in exporter sidecar that exposes metrics on port 56790.
• ServiceMonitor (named {memcached-name}-stats) is created automatically by KubeDB and tells Prometheus to scrape the exporter every 10 seconds.
• PrometheusRule is created by the memcached-alerts chart and contains all Memcached alert definitions grouped by concern: database health, provisioner, and ops-manager.
• Prometheus Operator evaluates every rule expression every 30 seconds and fires matching alerts to AlertManager.
• AlertManager groups, inhibits, and silences alerts, then routes them to configured receivers (Slack, email, PagerDuty, webhook, etc.).

Deploy Memcached with Monitoring Enabled

At first, let’s deploy a Memcached database with monitoring enabled. Below is the Memcached object we are going to create.

apiVersion: kubedb.com/v1
kind: Memcached
metadata:
  name: mc-alert-demo
  namespace: demo
spec:
  replicas: 1
  version: "1.6.40"
  deletionPolicy: WipeOut
  monitor:
    agent: prometheus.io/operator
    prometheus:
      serviceMonitor:
        interval: 10s
        labels:
          release: prometheus

Here,

• spec.monitor.agent: prometheus.io/operator tells KubeDB to create a ServiceMonitor resource managed by the Prometheus operator.
• spec.monitor.prometheus.serviceMonitor.labels.release: prometheus adds the release: prometheus label to the created ServiceMonitor, matching the Prometheus serviceMonitorSelector so the target is discovered automatically.

Let’s create the Memcached resource.

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2026.6.19/docs/examples/memcached/monitoring/mc-alert-demo.yaml
memcached.kubedb.com/mc-alert-demo created

Now, wait for the database to go into Ready state.

$ kubectl get memcached -n demo mc-alert-demo
NAME            VERSION   STATUS   AGE
mc-alert-demo   1.6.40    Ready    30s

KubeDB creates a dedicated stats service with the -stats suffix for monitoring.

$ kubectl get svc -n demo --selector="app.kubernetes.io/instance=mc-alert-demo"
NAME                    TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)     AGE
mc-alert-demo           ClusterIP   10.43.157.50   <none>        11211/TCP   30s
mc-alert-demo-pods      ClusterIP   None           <none>        11211/TCP   30s
mc-alert-demo-stats     ClusterIP   10.43.157.43   <none>        56790/TCP   30s

KubeDB also creates a ServiceMonitor that tells Prometheus where to scrape.

$ kubectl get servicemonitor -n demo
NAME                  AGE
mc-alert-demo-stats   30s

Verify that the ServiceMonitor carries the release: prometheus label so Prometheus discovers it.

$ kubectl get servicemonitor -n demo mc-alert-demo-stats \
    -o jsonpath='{.metadata.labels.release}'
prometheus

Step 1 — Install memcached-alerts

The memcached-alerts chart creates a PrometheusRule resource containing all Memcached alert definitions grouped by concern: database health, provisioner, and ops-manager.

Why the Helm release name matters

The chart derives the PromQL job/instance scoping (and the PrometheusRule name) from the Helm release name, not from a values field — so the release name must match the Memcached object’s name (mc-alert-demo) for the rules to be correctly scoped to this instance.

The chart’s default label is release: kube-prometheus-stack, so we must also override it at install time to match the Prometheus ruleSelector.

Install

$ helm upgrade -i mc-alert-demo oci://ghcr.io/appscode-charts/memcached-alerts \
    -n demo \
    --create-namespace \
    --version=v2026.7.14 \
    --set form.alert.labels.release=prometheus

Verify the PrometheusRule is created

$ kubectl get prometheusrule -n demo
NAME            AGE
mc-alert-demo   30s

Confirm the release: prometheus label is present.

$ kubectl get prometheusrule -n demo mc-alert-demo \
    -o jsonpath='{.metadata.labels.release}'
prometheus

Confirm Prometheus loaded the rules

Port-forward the Prometheus UI and open the Status → Rule health page.

$ kubectl port-forward -n monitoring \
    svc/prometheus-kube-prometheus-prometheus 9090:9090

Open http://localhost:9090/rules?search=memcached.

The memcached.database.demo.mc-alert-demo.rules group is visible with all rules showing OK, confirming that Prometheus has loaded and is evaluating the Memcached alert definitions every 30 seconds.

Verify End-to-End

1. Check the exporter is running

The exporter sidecar inside the Memcached pod serves metrics at :56790/metrics. A value of memcached_up 1 confirms the exporter can reach Memcached.

$ kubectl exec -n demo mc-alert-demo-0 -c exporter -- \
    wget -qO- localhost:56790/metrics | grep memcached_up
memcached_up 1

2. Check the Prometheus target is UP

Open http://localhost:9090/targets?search=mc-alert-demo.

The target serviceMonitor/demo/mc-alert-demo-stats/0 shows UP, confirming metrics are being scraped from mc-alert-demo-0 in the demo namespace.

3. Confirm all Memcached alerts are inactive

Open http://localhost:9090/alerts?search=memcached to see the Memcached alert groups.

All 6 rules in the memcached.database group show INACTIVE (6), meaning the database is healthy and no thresholds are breached.

4. Check AlertManager

Port-forward AlertManager to view any currently firing alerts.

$ kubectl port-forward -n monitoring \
    svc/prometheus-kube-prometheus-alertmanager 9093:9093

Open http://localhost:9093. With a healthy Memcached instance, no alerts for mc-alert-demo will be listed here.

Simulating a Firing Alert

The previous section confirmed that all alerts are INACTIVE while the database is healthy. This section walks through deliberately triggering the MemcachedDown critical alert so you can observe the full alert lifecycle — from firing in Prometheus through to the AlertManager dashboard — and then resolve it.

1. Stop the Memcached process

Kill the memcached process inside the pod. This crashes the main container so the exporter sidecar can no longer reach it and reports memcached_up 0 on the next scrape, while Kubernetes restarts the crashed container in the background.

$ kubectl exec -n demo mc-alert-demo-0 -c memcached -- kill 1

Wait 30–60 seconds for the next Prometheus scrape cycle (configured at 10 s) and rule-evaluation cycle (30 s) to register the failure.

2. Watch the alert fire in Prometheus

Open http://localhost:9090/alerts?search=memcached.

Because MemcachedDown has for: 0m (instant), it moves directly from INACTIVE to FIRING within one evaluation cycle.

3. Check the AlertManager dashboard

Open http://localhost:9093.

AlertManager shows the MemcachedDown alert. The alert card displays:

• Severity: critical
• Instance: mc-alert-demo-0 in the demo namespace
• job: mc-alert-demo-stats
• Started: timestamp when the alert first fired

AlertManager routes this alert to every receiver configured in your alertmanagerConfig (Slack, email, PagerDuty, webhook, etc.) based on your routing tree. If no receiver is configured, the alert is visible here but silently dropped.

4. Restore Memcached

Delete the pod so KubeDB recreates it cleanly.

$ kubectl delete pod -n demo mc-alert-demo-0

Once memcached_up returns to 1, Prometheus marks the alert INACTIVE again and AlertManager sends a resolved notification to all receivers.

Alert Reference

All alerts are scoped to the mc-alert-demo instance in the demo namespace via the PromQL label filters job="mc-alert-demo-stats" and namespace="demo".

Database Group

Fired based on live metrics from the Memcached exporter.

Provisioner Group

Monitors the KubeDB operator’s view of the Memcached resource phase.

OpsManager Group

Tracks MemcachedOpsRequest lifecycle during upgrades, scaling, and reconfiguration.

Customising Alerts

To override thresholds or disable specific alert groups, create a custom values file and upgrade the chart.

# custom-alerts.yaml
form:
  alert:
    labels:
      release: prometheus
    groups:
      database:
        enabled: warning
        rules:
          memcachedConnectionThrottled:
            enabled: true
            duration: "5m"
            val: 20        # fire at 20 throttled connections instead of the default 10
            severity: warning
      opsManager:
        enabled: "none"    # disable all ops-manager alerts

$ helm upgrade mc-alert-demo oci://ghcr.io/appscode-charts/memcached-alerts \
    -n demo \
    --version=v2026.7.14 \
    -f custom-alerts.yaml

Cleaning up

To remove all resources created in this tutorial, run the following commands.

# Remove the memcached-alerts release
$ helm uninstall mc-alert-demo -n demo

# Remove the Memcached instance
$ kubectl delete memcached -n demo mc-alert-demo

# Delete namespace
$ kubectl delete ns demo

Next Steps

• Monitor your Memcached database with KubeDB using builtin Prometheus.
• Monitor your Memcached database with KubeDB using Prometheus operator.
• Visualise Memcached metrics with Grafana Dashboard.
• Use private Docker registry to deploy Memcached with KubeDB.
• Want to hack on KubeDB? Check our contribution guidelines.