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Monitoring Memcached Using Prometheus operator

Prometheus operator provides simple and Kubernetes native way to deploy and configure Prometheus server. This tutorial will show you how to use Prometheus operator to monitor Memcached server deployed with KubeDB.

Before You Begin

At first, you need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using kind.
To learn how Prometheus monitoring works with KubeDB in general, please visit here.
We need a Prometheus operator instance running. If you don’t already have a running instance, deploy one following the docs from here.
To keep Prometheus resources isolated, we are going to use a separate namespace called monitoring to deploy respective monitoring resources. We are going to deploy database in demo namespace.
```
$ kubectl create ns monitoring
namespace/monitoring created

$ kubectl create ns demo
namespace/demo created
```

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

Find out required labels for ServiceMonitor

We need to know the labels used to select ServiceMonitor by a Prometheus crd. We are going to provide these labels in spec.monitor.prometheus.labels field of Memcached crd so that KubeDB creates ServiceMonitor object accordingly.

At first, let’s find out the available Prometheus server in our cluster.

$ kubectl get prometheus --all-namespaces
NAMESPACE    NAME                                    VERSION   DESIRED   READY   RECONCILED   AVAILABLE   AGE
monitoring   prometheus-kube-prometheus-prometheus   v2.54.1   1         1       True         True        3m

If you don’t have any Prometheus server running in your cluster, deploy one following the guide specified in Before You Begin section.

Now, let’s view the YAML of the available Prometheus server prometheus in monitoring namespace.

$ kubectl get prometheus -n monitoring prometheus-kube-prometheus-prometheus -o yaml
apiVersion: monitoring.coreos.com/v1
kind: Prometheus
metadata:
  annotations:
    meta.helm.sh/release-name: prometheus
    meta.helm.sh/release-namespace: monitoring
  creationTimestamp: "2024-09-17T13:24:28Z"
  generation: 1
  labels:
    app: kube-prometheus-stack-prometheus
    app.kubernetes.io/instance: prometheus
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/part-of: kube-prometheus-stack
    app.kubernetes.io/version: 62.7.0
    chart: kube-prometheus-stack-62.7.0
    heritage: Helm
    release: prometheus
  name: prometheus-kube-prometheus-prometheus
  namespace: monitoring
  resourceVersion: "396596"
  uid: ee3cb256-1f08-4bd4-966a-2050822affbf
spec:
  alerting:
    alertmanagers:
    - apiVersion: v2
      name: prometheus-kube-prometheus-alertmanager
      namespace: monitoring
      pathPrefix: /
      port: http-web
  automountServiceAccountToken: true
  enableAdminAPI: false
  evaluationInterval: 30s
  externalUrl: http://prometheus-kube-prometheus-prometheus.monitoring:9090
  hostNetwork: false
  image: quay.io/prometheus/prometheus:v2.54.1
  listenLocal: false
  logFormat: logfmt
  logLevel: info
  paused: false
  podMonitorNamespaceSelector: {}
  podMonitorSelector:
    matchLabels:
      release: prometheus
  portName: http-web
  probeNamespaceSelector: {}
  probeSelector:
    matchLabels:
      release: prometheus
  replicas: 1
  retention: 10d
  routePrefix: /
  ruleNamespaceSelector: {}
  ruleSelector:
    matchLabels:
      release: prometheus
  scrapeConfigNamespaceSelector: {}
  scrapeConfigSelector:
    matchLabels:
      release: prometheus
  scrapeInterval: 30s
  securityContext:
    fsGroup: 2000
    runAsGroup: 2000
    runAsNonRoot: true
    runAsUser: 1000
    seccompProfile:
      type: RuntimeDefault
  serviceAccountName: prometheus-kube-prometheus-prometheus
  serviceMonitorNamespaceSelector: {}
  serviceMonitorSelector:
    matchLabels:
      release: prometheus
  shards: 1
  tsdb:
    outOfOrderTimeWindow: 0s
  version: v2.54.1
  walCompression: true
status:
  availableReplicas: 1
  conditions:
  - lastTransitionTime: "2024-09-17T13:24:45Z"
    message: ""
    observedGeneration: 1
    reason: ""
    status: "True"
    type: Available
  - lastTransitionTime: "2024-09-17T13:24:45Z"
    message: ""
    observedGeneration: 1
    reason: ""
    status: "True"
    type: Reconciled
  paused: false
  replicas: 1
  selector: app.kubernetes.io/instance=prometheus-kube-prometheus-prometheus,app.kubernetes.io/managed-by=prometheus-operator,app.kubernetes.io/name=prometheus,operator.prometheus.io/name=prometheus-kube-prometheus-prometheus,prometheus=prometheus-kube-prometheus-prometheus
  shardStatuses:
  - availableReplicas: 1
    replicas: 1
    shardID: "0"
    unavailableReplicas: 0
    updatedReplicas: 1
  shards: 1
  unavailableReplicas: 0
  updatedReplicas: 1

Notice the spec.serviceMonitorSelector section. Here, release: prometheus label is used to select ServiceMonitor crd. So, we are going to use this label in spec.monitor.prometheus.labels field of Memcached crd.

Deploy Memcached with Monitoring Enabled

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

apiVersion: kubedb.com/v1
kind: Memcached
metadata:
  name: memcached
  namespace: demo
spec:
  replicas: 1
  version: "1.6.22"
  deletionPolicy: WipeOut
  podTemplate:
    spec:
      containers:
      - name: memcached
        resources:
          limits:
            cpu: 500m
            memory: 128Mi
          requests:
            cpu: 250m
            memory: 64Mi
  monitor:
    agent: prometheus.io/operator
    prometheus:
      serviceMonitor:
        labels:
          release: prometheus
        interval: 10s

Here,

monitor.agent: prometheus.io/operator indicates that we are going to monitor this server using Prometheus operator.
monitor.prometheus.namespace: monitoring specifies that KubeDB should create ServiceMonitor in monitoring namespace.
monitor.prometheus.labels specifies that KubeDB should create ServiceMonitor with these labels.
monitor.prometheus.interval indicates that the Prometheus server should scrape metrics from this database with 10 seconds interval.

Let’s create the Memcached object that we have shown above,

$ kubectl create -f https://github.com/kubedb/docs/raw/v2024.9.30/docs/examples/memcached/monitoring/memcached.yaml
memcached.kubedb.com/memcached created

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

$ kubectl get mc -n demo memcached
NAME        VERSION   STATUS   AGE
memcached   1.6.22    Ready    2m

KubeDB will create a separate stats service with name {Memcached crd name}-stats for monitoring purpose.

$ kubectl get svc -n demo --selector="app.kubernetes.io/instance=memcached"
NAME              TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)     AGE
memcached         ClusterIP   10.96.91.51   <none>        11211/TCP   3m9s
memcached-pods    ClusterIP   None          <none>        11211/TCP   3m9s
memcached-stats   ClusterIP   10.96.50.21   <none>        56790/TCP   3m9s

Here, memcached-stats service has been created for monitoring purpose.

Let’s describe this stats service.

$ kubectl describe svc -n demo memcached-stats
Name:              memcached-stats
Namespace:         demo
Labels:            app.kubernetes.io/component=database
                   app.kubernetes.io/instance=memcached
                   app.kubernetes.io/managed-by=kubedb.com
                   app.kubernetes.io/name=memcacheds.kubedb.com
                   kubedb.com/role=stats
Annotations:       monitoring.appscode.com/agent: prometheus.io/operator
Selector:          app.kubernetes.io/instance=memcached,app.kubernetes.io/managed-by=kubedb.com,app.kubernetes.io/name=memcacheds.kubedb.com
Type:              ClusterIP
IP Family Policy:  SingleStack
IP Families:       IPv4
IP:                10.96.50.21
IPs:               10.96.50.21
Port:              metrics  56790/TCP
TargetPort:        metrics/TCP
Endpoints:         10.244.0.7:56790
Session Affinity:  None
Events:            <none>

Notice the Labels and Port fields. ServiceMonitor will use these information to target its endpoints.

KubeDB will also create a ServiceMonitor crd in monitoring namespace that select the endpoints of memcached-stats service. Verify that the ServiceMonitor crd has been created.

$ kubectl get servicemonitor -n demo
NAME              AGE
memcached-stats   5m

Let’s verify that the ServiceMonitor has the label that we had specified in spec.monitor section of Memcached crd.

$ kubectl get servicemonitor -n demo memcached-stats -o yaml
apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  creationTimestamp: "2024-09-17T13:32:15Z"
  generation: 1
  labels:
    app.kubernetes.io/component: database
    app.kubernetes.io/instance: memcached
    app.kubernetes.io/managed-by: kubedb.com
    app.kubernetes.io/name: memcacheds.kubedb.com
    release: prometheus
  name: memcached-stats
  namespace: demo
  ownerReferences:
  - apiVersion: v1
    blockOwnerDeletion: true
    controller: true
    kind: Service
    name: memcached-stats
    uid: 6c05bc95-c26c-4b0b-988f-2ecc58e983bf
  resourceVersion: "397210"
  uid: b14633ab-338d-43a6-87bc-2ab77d761cf4
spec:
  endpoints:
  - honorLabels: true
    path: /metrics
    port: metrics
  namespaceSelector:
    matchNames:
    - demo
  selector:
    matchLabels:
      app.kubernetes.io/component: database
      app.kubernetes.io/instance: memcached
      app.kubernetes.io/managed-by: kubedb.com
      app.kubernetes.io/name: memcacheds.kubedb.com
      kubedb.com/role: stats

Notice that the ServiceMonitor has label release: prometheus that we had specified in Memcached crd.

Also notice that the ServiceMonitor has selector which match the labels we have seen in the memcached-stats service. It also, target the prom-http port that we have seen in the stats service.

Verify Monitoring Metrics

At first, let’s find out the respective Prometheus pod for prometheus Prometheus server.

$ kubectl get pod -n monitoring -l=app.kubernetes.io/name=prometheus
NAME                                                 READY   STATUS    RESTARTS   AGE
prometheus-prometheus-kube-prometheus-prometheus-0   2/2     Running   0          16m

Prometheus server is listening to port 9090 of prometheus-prometheus-0 pod. We are going to use port forwarding to access Prometheus dashboard.

Run following command on a separate terminal to forward the port 9090 of prometheus-prometheus-0 pod,

$ kubectl port-forward -n monitoring svc/prometheus-kube-prometheus-prometheus 9090
Forwarding from 127.0.0.1:9090 -> 9090
Forwarding from [::1]:9090 -> 9090

Now, we can access the dashboard at localhost:9090. Open http://localhost:9090 in your browser. You should see prom-http endpoint of memcached-stats service as one of the targets.

Prometheus Target

Check the endpoint and service labels marked by red rectangle. It verifies that the target is our expected database. Now, you can view the collected metrics and create a graph from homepage of this Prometheus dashboard. You can also use this Prometheus server as data source for Grafana and create beautiful dashboard with collected metrics.

Cleaning up

To cleanup the Kubernetes resources created by this tutorial, run following commands

# cleanup database
kubectl delete -n demo mc/memcached

# cleanup prometheus resources
kubectl delete -n monitoring prometheus prometheus
kubectl delete -n monitoring clusterrolebinding prometheus
kubectl delete -n monitoring clusterrole prometheus
kubectl delete -n monitoring serviceaccount prometheus
kubectl delete -n monitoring service prometheus-operated

# cleanup prometheus operator resources
kubectl delete -n monitoring deployment prometheus-operator
kubectl delete -n dmeo serviceaccount prometheus-operator
kubectl delete clusterrolebinding prometheus-operator
kubectl delete clusterrole prometheus-operator

# delete namespace
kubectl delete ns monitoring
kubectl delete ns demo

Next Steps

Monitor your Memcached server with KubeDB using out-of-the-box builtin-Prometheus.
Detail concepts of Memcached object.
Use private Docker registry to deploy Memcached with KubeDB.
Want to hack on KubeDB? Check our contribution guidelines.

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