PostgreSQL: PostgreSQL Operator for Kubernetes, and its Prometheus monitoring

By | 09/23/2022
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So, we’ve launched Druid, see Apache Druid: Overview, Running in Kubernetes, and Monitoring with Prometheus . So far, a local Apache Derby database is used as the default storage for metadata .

Next, we will switch Druid to PostgreSQL, and later we will remove ZooKeeper from the cluster setup.

To begin with, let’s start a PostgreSQL cluster in Kubernetes, add the PostgreSQL Exporter for Prometheus, and configure metrics collection.

We will launch again in Minikube , for PostgreSQL, we will use Zalando Operator , and will add the PostgreSQL Exporter as a sidecar container .

We will not dig deep into the Operator yet, although it is very interesting, so we will play with it somehow. For now, we just need to monitor it.

Documentation – Administrator Guide .

Starting the PostgreSQL operator

Create a namespace:

[simterm]

$ kubectl create ns postgres-operator
namespace/postgres-operator created

[/simterm]

Add a Helm repository:

[simterm]

$ helm repo add postgres-operator-charts https://opensource.zalando.com/postgres-operator/charts/postgres-operator

[/simterm]

Install the operator itself:

[simterm]

$ helm -n postgres-operator install postgres-operator postgres-operator-charts/postgres-operator

[/simterm]

If need, add a WebUI for the operator:

[simterm]

$ helm repo add postgres-operator-ui-charts https://opensource.zalando.com/postgres-operator/charts/postgres-operator-ui
$ helm -n postgres-operator install postgres-operator-ui postgres-operator-ui-charts/postgres-operator-ui

[/simterm]

Check pods:

[simterm]

$ kubectl -n postgres-operator get pods
NAME                                    READY   STATUS    RESTARTS   AGE
postgres-operator-649799f4bd-dz5bl      1/1     Running   0          82s
postgres-operator-ui-5cfff55c65-v4bjj   1/1     Running   0          22s

[/simterm]

Povide access for yourself to the Operator’s web intrerface service:

[simterm]

$ kubectl port-forward svc/postgres-operator-ui 8081:80
Forwarding from 127.0.0.1:8081 -> 8081
Forwarding from [::1]:8081 -> 8081

[/simterm]

Check it:

We will not do anything here, will take ready-made examples of the cluster configuration.

Starting a PostgreSQL cluster

Clone the Operator’s repository:

[simterm]

$ https://github.com/zalando/postgres-operator.git
$ cd postgres-operator/

[/simterm]

There are several examples in the manifests catalog, let’s take the manifests/minimal-master-replica-svcmonitor.yaml file – it describes a namespace, a cluster, user, databases, two Service, and two ServiceMonitors + Sidecars with Prometheus Exporter.

Apply it:

[simterm]

$ kubectl apply -f manifests/minimal-master-replica-svcmonitor.yaml
namespace/test-pg created
postgresql.acid.zalan.do/acid-minimal-cluster created
service/acid-minimal-cluster-svc-metrics-master created
service/acid-minimal-cluster-svc-metrics-replica created
servicemonitor.monitoring.coreos.com/acid-minimal-cluster-svcm-master created
servicemonitor.monitoring.coreos.com/acid-minimal-cluster-svcm-replica created

[/simterm]

Check the cluster:

[simterm]

$ kk -n test-pg get postgresql
NAME                   TEAM   VERSION   PODS   VOLUME   CPU-REQUEST   MEMORY-REQUEST   AGE     STATUS
acid-minimal-cluster   acid   13        2      1Gi                                     2m21s   Running

[/simterm]

Its Pods:

[simterm]

$ kk -n test-pg get po
NAME                     READY   STATUS    RESTARTS   AGE
acid-minimal-cluster-0   2/2     Running   0          37s
acid-minimal-cluster-1   1/2     Running   0          24s

[/simterm]

Each one has its own role, which is set in the labels – spilo-role=masteror spilo-role=replica.

PostgreSQL users

See docs here>>> and here>>> .

Users are described in the – surprise – users block:

[simterm]

$ kubectl -n test-pg get postgresql -o yaml
...
    users:
      foo_user: []
      zalando:
      - superuser
      - createdb
...

[/simterm]

And Operator will create a dedicated Kubernetes Secret for each of them:

[simterm]

$ kk -n test-pg get secret
NAME                                                                 TYPE     DATA   AGE
foo-user.acid-minimal-cluster.credentials.postgresql.acid.zalan.do   Opaque   2      38m
postgres.acid-minimal-cluster.credentials.postgresql.acid.zalan.do   Opaque   2      38m
standby.acid-minimal-cluster.credentials.postgresql.acid.zalan.do    Opaque   2      38m
zalando.acid-minimal-cluster.credentials.postgresql.acid.zalan.do    Opaque   2      38m

[/simterm]

Which are then mapped to pods through variables:

[simterm]

$ kubectl -n test-pg get statefulsets acid-minimal-cluster -o yaml
...
      - env:
        - name: POD_NAME
          valueFrom:
            fieldRef:
              apiVersion: v1
              fieldPath: metadata.name
        - name: POD_NAMESPACE
          valueFrom:
            fieldRef:
              apiVersion: v1
              fieldPath: metadata.namespace
        - name: POSTGRES_USER
          value: postgres
        - name: POSTGRES_PASSWORD
          valueFrom:
            secretKeyRef:
              key: password
              name: postgres.acid-minimal-cluster.credentials.postgresql.acid.zalan.do
...

[/simterm]

Well, let’s check.

Let’s get the password:

[simterm]

$ kubectl -n test-pg get secret postgres.acid-minimal-cluster.credentials.postgresql.acid.zalan.do -o 'jsonpath={.data.password}' | base64 -d
CcWdAaqvPA8acxwIpVyM8UHkds2QG3opC3KD7rO1TxITQ1q31cwYLTswzfBeTVsN

[/simterm]

Open its port to access it locally:

[simterm]

$ kubectl -n test-pg port-forward acid-minimal-cluster-0 6432:5432

[/simterm]

Log in and check the databases:

[simterm]

$ psql -U postgres -h localhost -p 6432
Password for user postgres: 
psql (14.5, server 13.7 (Ubuntu 13.7-1.pgdg18.04+1))
SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, bits: 256, compression: off)
Type "help" for help.

postgres=# \l
                                  List of databases
   Name    |   Owner   | Encoding |   Collate   |    Ctype    |   Access privileges   
-----------+-----------+----------+-------------+-------------+-----------------------
 bar       | bar_owner | UTF8     | en_US.utf-8 | en_US.utf-8 | 
 foo       | zalando   | UTF8     | en_US.utf-8 | en_US.utf-8 | 
 postgres  | postgres  | UTF8     | en_US.utf-8 | en_US.utf-8 | 
 template0 | postgres  | UTF8     | en_US.utf-8 | en_US.utf-8 | =c/postgres          +
           |           |          |             |             | postgres=CTc/postgres
 template1 | postgres  | UTF8     | en_US.utf-8 | en_US.utf-8 | =c/postgres          +
           |           |          |             |             | postgres=CTc/postgres
(5 rows)

postgres=#

[/simterm]

PostgreSQL Prometheus Exporter

See Sidecar definitions .

We already have a sidecar – it was added from the manifest, and in each Pod, we currently have two containers – PostgreSQL itself, and its Exporter:

[simterm]

$ kk -n test-pg get po acid-minimal-cluster-0 -o jsonpath='{.spec.containers[*].name}'
postgres exporter

[/simterm]

Let’s see if there are metrics there – open the port:

[simterm]

$ kubectl -n test-pg port-forward svc/acid-minimal-cluster-svc-metrics-master 9187:9187
Forwarding from 127.0.0.1:9187 -> 9187
Forwarding from [::1]:9187 -> 9187

[/simterm]

And we see that we do not see anything, and the cluster is kind of “dead” – pg_up == 0:

[simterm]

$ curl -s localhost:9187/metrics | grep pg_ | grep -v '#'
pg_exporter_last_scrape_duration_seconds 1.00031302
pg_exporter_last_scrape_error 1
pg_exporter_scrapes_total 9
pg_up 0

[/simterm]

Why – because the exporter must have access data, i.e. login-password.

In the configuration of the sidecar, add new variables, see Environment Variables :

...
      env:
      - name: "DATA_SOURCE_URI"
        value: "$(POD_NAME)/postgres?sslmode=require"
      - name: "DATA_SOURCE_USER"
        value: "$(POSTGRES_USER)"
      - name: "DATA_SOURCE_PASS"
        value: "$(POSTGRES_PASSWORD)"
      - name: "PG_EXPORTER_AUTO_DISCOVER_DATABASES"
        value: "true"
...

That is, the Operator creates a StatefulSet in which it sets the variables POSTGRES_USERand POSTGRES_PASSWORD, which we use for the sidecar to set its own variables.

Save updates and apply them:

[simterm]

$ kubectl apply -f manifests/minimal-master-replica-svcmonitor.yaml

[/simterm]

Check the variables in the pod itself:

[simterm]

$ kubectl -n test-pg get po acid-minimal-cluster-0 -o yaml
...
  - env:
    - name: POD_NAME
      valueFrom:
        fieldRef:
          apiVersion: v1
          fieldPath: metadata.name
    - name: POD_NAMESPACE
      valueFrom:
        fieldRef:
          apiVersion: v1
          fieldPath: metadata.namespace
    - name: POSTGRES_USER
      value: postgres
    - name: POSTGRES_PASSWORD
      valueFrom:
        secretKeyRef:
          key: password
          name: postgres.acid-minimal-cluster.credentials.postgresql.acid.zalan.do
    - name: DATA_SOURCE_URI
      value: $(POD_NAME)/postgres?sslmode=require
    - name: DATA_SOURCE_USER
      value: $(POSTGRES_USER)
    - name: DATA_SOURCE_PASS
      value: $(POSTGRES_PASSWORD)
    - name: PG_EXPORTER_AUTO_DISCOVER_DATABASES
      value: "true"
...

[/simterm]

And check the metrics again in the exporter:

[simterm]

$ curl -s localhost:9187/metrics | grep pg_ | grep -v '#' | tail -5
pg_stat_replication_pg_current_wal_lsn_bytes{application_name="acid-minimal-cluster-0",client_addr="172.17.0.17",server="acid-minimal-cluster-1:5432",slot_name="182",state="streaming"} 1.52655344e+08
pg_stat_replication_pg_wal_lsn_diff{application_name="acid-minimal-cluster-0",client_addr="172.17.0.17",server="acid-minimal-cluster-1:5432",slot_name="182",state="streaming"} 0
pg_stat_replication_reply_time{application_name="acid-minimal-cluster-0",client_addr="172.17.0.17",server="acid-minimal-cluster-1:5432",slot_name="182",state="streaming"} 1.663625745e+09
pg_static{server="acid-minimal-cluster-1:5432",short_version="13.7.0",version="PostgreSQL 13.7 (Ubuntu 13.7-1.pgdg18.04+1) on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0, 64-bit"} 1
pg_up 1

[/simterm]

pg_up == 1 –  yay! It works!

Prometehus ServiceMonitors

Open the port to access Prometheus itself:

[simterm]

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

[/simterm]

Check Status > Service Discovery – we don’t see PostgreSQL here:

ServiceMonitors are already created from the manifest:

[simterm]

$ kubectl -n test-pg get servicemonitor
NAME                                AGE
acid-minimal-cluster-svcm-master    65m
acid-minimal-cluster-svcm-replica   65m

[/simterm]

Let’s repeat the “dirty hack” as we did for Druid – add a label to them "release": "kube-prometheus-stack", wait a minute or two, and check again:

And we got our PostgreSQL’s cluster metrics in the Prometheus graphs:

Done.