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Monitoring FerretDB 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 FerretDB database 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, you can deploy one using this helm chart here.
To keep Prometheus resources isolated, we are going to use a separate namespace called monitoring to deploy the prometheus operator helm chart. 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/ferretdb 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.serviceMonitor.labels field of FerretDB 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        13m

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: "2024-10-14T17:17:25Z"
  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: 65.2.0
    chart: kube-prometheus-stack-65.2.0
    heritage: Helm
    release: prometheus
  name: prometheus-kube-prometheus-prometheus
  namespace: monitoring
  resourceVersion: "58118"
  uid: b1bf237b-2fdc-459c-b92f-e087a1119f33
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: "2024-10-14T17:27:17Z"
      message: ""
      observedGeneration: 1
      reason: ""
      status: "True"
      type: Available
    - lastTransitionTime: "2024-10-14T17:27:17Z"
      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.serviceMonitor.labels field of FerretDB crd.

Deploy FerretDB with Monitoring Enabled

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

apiVersion: kubedb.com/v1alpha2
kind: FerretDB
metadata:
  name: coreos-prom-fr
  namespace: demo
spec:
  version: "1.18.0"
  storage:
    accessModes:
      - ReadWriteOnce
    resources:
      requests:
        storage: 500Mi
  backend:
    externallyManaged: false
  deletionPolicy: WipeOut
  replicas: 2
  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.serviceMonitor.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 FerretDB object that we have shown above,

$ kubectl create -f https://github.com/kubedb/docs/raw/v2024.12.18/docs/examples/ferretdb/monitoring/coreos-prom-fr.yaml
ferretdb.kubedb.com/coreos-prom-fr created

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

$ kubectl get fr -n demo coreos-prom-fr
NAME             NAMESPACE   VERSION   STATUS   AGE
coreos-prom-fr   demo        1.18.0    Ready    111s

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

$ kubectl get svc -n demo --selector="app.kubernetes.io/instance=coreos-prom-fr"
NAME                   TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)     AGE
coreos-prom-fr         ClusterIP   10.96.234.253   <none>        27017/TCP   2m16s
coreos-prom-fr-stats   ClusterIP   10.96.27.143    <none>        56790/TCP   2m16s

Here, coreos-prom-fr-stats service has been created for monitoring purpose.

Let’s describe this stats service.

$ kubectl describe svc -n demo coreos-prom-fr-stats

Name:              coreos-prom-fr-stats
Namespace:         demo
Labels:            app.kubernetes.io/component=database
  app.kubernetes.io/instance=coreos-prom-fr
  app.kubernetes.io/managed-by=kubedb.com
  app.kubernetes.io/name=ferretdbs.kubedb.com
  kubedb.com/role=stats
Annotations:       monitoring.appscode.com/agent: prometheus.io/operator
Selector:          app.kubernetes.io/instance=coreos-prom-fr,app.kubernetes.io/managed-by=kubedb.com,app.kubernetes.io/name=ferretdbs.kubedb.com
Type:              ClusterIP
IP Family Policy:  SingleStack
IP Families:       IPv4
IP:                10.96.27.143
IPs:               10.96.27.143
Port:              metrics  56790/TCP
TargetPort:        metrics/TCP
Endpoints:         10.244.0.59:8080,10.244.0.60:8080
Session Affinity:  None
Events:            <none>

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

KubeDB will also create a ServiceMonitor crd in demo namespace that select the endpoints of coreos-prom-fr-stats service. Verify that the ServiceMonitor crd has been created.

$ kubectl get servicemonitor -n demo
NAME                              AGE
coreos-prom-fr-pg-backend-stats   3m33s
coreos-prom-fr-stats              2m24s

If backend Postgres is managed by KubeDB, KubeDB operator will also enable monitoring to backend Postgres. That’s why coreos-prom-fr-pg-backend-stats ServiceMonitor also created. To look at the more details of KubeDB managed Postgres monitoring, you can look at this documentation.

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

$ kubectl get servicemonitor -n demo coreos-prom-fr-stats -o yaml

apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  creationTimestamp: "2024-10-14T17:35:38Z"
  generation: 1
  labels:
    app.kubernetes.io/component: database
    app.kubernetes.io/instance: coreos-prom-fr
    app.kubernetes.io/managed-by: kubedb.com
    app.kubernetes.io/name: ferretdbs.kubedb.com
    release: prometheus
  name: coreos-prom-fr-stats
  namespace: demo
  ownerReferences:
    - apiVersion: v1
      blockOwnerDeletion: true
      controller: true
      kind: Service
      name: coreos-prom-fr-stats
      uid: d0811d68-6e31-4357-b35a-8a7793ab4918
  resourceVersion: "59094"
  uid: cfa29869-8000-44fe-bc9b-e7e78b08da36
spec:
  endpoints:
    - honorLabels: true
      interval: 10s
      path: /debug/metrics
      port: metrics
  namespaceSelector:
    matchNames:
      - demo
  selector:
    matchLabels:
      app.kubernetes.io/component: database
      app.kubernetes.io/instance: coreos-prom-fr
      app.kubernetes.io/managed-by: kubedb.com
      app.kubernetes.io/name: ferretdbs.kubedb.com
      kubedb.com/role: stats

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

Also notice that the ServiceMonitor has selector which match the labels we have seen in the coreos-prom-fr-stats service. It also, target the metrics 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          27m

Prometheus server is listening to port 9090 of prometheus-prometheus-kube-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-kube-prometheus-prometheus-0 pod,

$ kubectl port-forward -n monitoring prometheus-prometheus-kube-prometheus-prometheus-0 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 metrics endpoint of coreos-prom-fr-stats service as one of the targets.

Prometheus Target

Check the endpoint and service labels marked by the red rectangles. 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 a beautiful dashboard with collected metrics.

Cleaning up

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

kubectl delete -n demo fr/coreos-prom-fr
kubectl delete ns demo

Next Steps

Monitor your FerretDB database with KubeDB using out-of-the-box builtin-Prometheus.
Detail concepts of FerretDB object.
Detail concepts of FerretDBVersion object.
Want to hack on KubeDB? Check our contribution guidelines.

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