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Monitoring PostgreSQL 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 PostgreSQL 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.
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
```
We need a Prometheus operator instance running. If you don’t already have a running instance, deploy one following the docs from here.
If you already don’t have a Prometheus server running, deploy one following tutorial from here.

Note: YAML files used in this tutorial are stored in docs/examples/postgres 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 PostgreSQL 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         AGE
monitoring   prometheus   18m

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 -o yaml
apiVersion: monitoring.coreos.com/v1
kind: Prometheus
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: |
      {"apiVersion":"monitoring.coreos.com/v1","kind":"Prometheus","metadata":{"annotations":{},"labels":{"prometheus":"prometheus"},"name":"prometheus","namespace":"monitoring"},"spec":{"replicas":1,"resources":{"requests":{"memory":"400Mi"}},"serviceAccountName":"prometheus","serviceMonitorSelector":{"matchLabels":{"k8s-app":"prometheus"}}}}      
  creationTimestamp: 2019-01-03T13:41:51Z
  generation: 1
  labels:
    prometheus: prometheus
  name: prometheus
  namespace: monitoring
  resourceVersion: "44402"
  selfLink: /apis/monitoring.coreos.com/v1/namespaces/monitoring/prometheuses/prometheus
  uid: 5324ad98-0f5d-11e9-b230-080027f306f3
spec:
  replicas: 1
  resources:
    requests:
      memory: 400Mi
  serviceAccountName: prometheus
  serviceMonitorSelector:
    matchLabels:
      k8s-app: prometheus

Notice the spec.serviceMonitorSelector section. Here, k8s-app: prometheus label is used to select ServiceMonitor crd. So, we are going to use this label in spec.monitor.prometheus.labels field of PostgreSQL crd.

Deploy PostgreSQL with Monitoring Enabled

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

apiVersion: kubedb.com/v1alpha2
kind: Postgres
metadata:
  name: coreos-prom-postgres
  namespace: demo
spec:
  version: "13.2"
  terminationPolicy: WipeOut
  storage:
    storageClassName: "standard"
    accessModes:
    - ReadWriteOnce
    resources:
      requests:
        storage: 1Gi
  monitor:
    agent: prometheus.io/operator
    prometheus:
      serviceMonitor:
        labels:
          k8s-app: 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 PostgreSQL object that we have shown above,

$ kubectl create -f https://github.com/kubedb/docs/raw/v2021.06.23/docs/examples/postgres/monitoring/coreos-prom-postgres.yaml
postgresql.kubedb.com/coreos-prom-postgres created

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

$ kubectl get pg -n demo coreos-prom-postgres
NAME                   VERSION    STATUS    AGE
coreos-prom-postgres   10.2-v5    Running   38s

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

$ kubectl get svc -n demo --selector="app.kubernetes.io/instance=coreos-prom-postgres"
NAME                            TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)     AGE
coreos-prom-postgres            ClusterIP   10.107.102.123   <none>        5432/TCP    58s
coreos-prom-postgres-replicas   ClusterIP   10.109.11.171    <none>        5432/TCP    58s
coreos-prom-postgres-stats      ClusterIP   10.110.218.172   <none>        56790/TCP   51s

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

Let’s describe this stats service.

$ kubectl describe svc -n demo coreos-prom-postgres-stats
Name:              coreos-prom-postgres-stats
Namespace:         demo
Labels:            app.kubernetes.io/name=postgreses.kubedb.com
                   app.kubernetes.io/instance=coreos-prom-postgres
Annotations:       monitoring.appscode.com/agent: prometheus.io/operator
Selector:          app.kubernetes.io/name=postgreses.kubedb.com,app.kubernetes.io/instance=coreos-prom-postgres
Type:              ClusterIP
IP:                10.110.218.172
Port:              prom-http  56790/TCP
TargetPort:        prom-http/TCP
Endpoints:         172.17.0.7:56790
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 coreos-prom-postgres-stats service. Verify that the ServiceMonitor crd has been created.

$ kubectl get servicemonitor -n monitoring
NAME                               AGE
kubedb-demo-coreos-prom-postgres   1m

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

$ kubectl get servicemonitor -n monitoring kubedb-demo-coreos-prom-postgres -o yaml
apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  creationTimestamp: 2019-01-03T15:47:08Z
  generation: 1
  labels:
    k8s-app: prometheus
    monitoring.appscode.com/service: coreos-prom-postgres-stats.demo
  name: kubedb-demo-coreos-prom-postgres
  namespace: monitoring
  resourceVersion: "53969"
  selfLink: /apis/monitoring.coreos.com/v1/namespaces/monitoring/servicemonitors/kubedb-demo-coreos-prom-postgres
  uid: d3c419ad-0f6e-11e9-b230-080027f306f3
spec:
  endpoints:
  - honorLabels: true
    interval: 10s
    path: /metrics
    port: prom-http
  namespaceSelector:
    matchNames:
    - demo
  selector:
    matchLabels:
      app.kubernetes.io/name: postgreses.kubedb.com
      app.kubernetes.io/instance: coreos-prom-postgres

Notice that the ServiceMonitor has label k8s-app: prometheus that we had specified in PostgreSQL crd.

Also notice that the ServiceMonitor has selector which match the labels we have seen in the coreos-prom-postgres-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=prometheus
NAME                      READY   STATUS    RESTARTS   AGE
prometheus-prometheus-0   3/3     Running   1          63m

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 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 prom-http endpoint of coreos-prom-postgres-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 pg/coreos-prom-postgres

# 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 PostgreSQL database with KubeDB using built-in Prometheus.
Want to hack on KubeDB? Check our contribution guidelines.

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