How to Deploy Postgres on Kubernetes

Published: August 25, 2020 by Author's Photo Shane Rainville | Reading time: 6 minutes.
Learn how to deploy a PostgreSQL container instance in Kubernetes with persistent storage, configMaps, and secrets. Also, how to backup a PostgreSQL database in Kubernetes.

In this guide, you will learn how to deploy and run a Postres database server instance in Kubernetes.

What’s Covered

  • Deploying containerized Postgress instances in Kubernetes
  • Using Kubernetes Secrets to store sensitive configurations
  • Using Kubernetes ConfigMaps to store non-sensitive configurations
  • Using Kuberentes Persistent Volumes to persist databases
  • Using Kubernetes CronJobs to backup databases

PostgreSQL Docker Image

PostgreSQL offers an Official PostgreSQL Docker image through Docker Hub. It always recommended to use official images over third-party or self-created images. In this guide we will use the official image to deploy the database server in Kubernetes.

Environment Variables

Environment variables allow us to configure environment specific parameters for Docker images that support them. The official Postgres images support the following environment variables.

  • POSTGRES_PASSWORD (required) is used to set the superuser password.
  • POSTGRES_USER (optional) is used to create a superuser with the name set in the environment variable.
  • POSTGRES_DB (optional) is used to create a database to be used as the default.

We will dive into setting these values in the next section: Configuring PostreSQL. For now, it’s good to understand what variables are available for configuring your instance.

Configuring PostgreSQL

ConfigMaps

ConfigMaps provide a means to store environment parameters in Kubernetes, to be fetched by a Pod when it starts. Values in a ConfigMap and be key-pair strings, entire files, or both. Which you use depends on your implementation.

Data stored in a ConfigMap not encrypted. These Kubernetes resources should be only be used with data that is non-sensitive.

apiVersion: v1
kind: ConfigMap
metadata:
  name: postgres
data:
  POSTGRES_DB: myapp_production

Secrets

For sensitive data, such as user credentials, Kubernetes Secrets allow you to more safely store data in the cluster. Like ConfigMap, the values in a Secret can be fetched by a Pod during startup.

Kubernetes Secrets can be expressed using a manifest, like any other resource. However, due to their sensitive nature it is not recommended to store secret manifest files in your version control system with actual values.

To create a secret resource named postgres for storing a superuser username and password, use the kubectl create secret command.

kubectl create secret generic postgres \
--from-literal=POSTGRES_USER="root" \
--from-literal=POSTGRES_PASSWORD="my-super-secret-password"

Alternatively, if you do wish to use a manifest file, create a new postgres-secrets.yaml file with the following structure.

If you choose to store your secret manifest in version control, consider removing the actual values. By keeping just the structure your operators will know which parameters must be set.
apiVersion: v1
kind: Secret
metadata:
  name: postgres
data:
  POSTGRES_PASSWORD: bXktc3VwZXItc2VjcmV0LXBhc3N3b3Jk
stringData:
  POSTGRES_USER: root

Notice the value used for POSTGRES_PASSWORD. That value is not the actual password. Rather, it is base64 encoded string of the password. Do not confuse base64 encoding with encyption. It merely serves to obfuscate the password to prevent prying eyes from easily reading it.

To base64 encode a string in Linux and OSX, you use the base64 command.

echo -n 'my-super-secret-password' | base64

To create the secret resource for Postgres, apply the manifest.

kubectl apply -f postgres-secrets.yaml

Deploying PostgreSQL

While containers in Kubernetes run from Pods a Postgres server should not be deployed as a pod. Rather, a Kubernetes Deployment should be used.

Persistent Volume Claim

Database servers are stateful and, therefore, their databases are expected to be persistent. A container, on the other hand, is ephermeral with no expectation for persisting state. This is obviously problemmatic with stateful applications like database servers.

A Kubernetes Persistent Volume is a volume that attaches to a Pod or group of Pods. Data writtent to it persists and is available to any Pod that mounts it. In most use cases it can be thought of as a network filesystem (NFS), as the behaviour is similar.

To mount a Persistent Volume to a Pod a Persistent Volume Claim must exist.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: postgres-pv-claim
  labels:
    app: postgres
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi

Deployment Manifest

A Kubernetes deployment manifest for Postgres would look similar to the example.

  • Create a single pod replica.
  • Use a base image Postgres 12.4 runing on Alpine Linux.
  • Expose port 5432.
  • Environment variables set using parameters found in a Secret manifest
  • Environment variables set using parameters found in a ConfigMap.
  • Mount a Persistent Volume using a Persistent Volume Claim for the Postgres database files.
apiVersion: apps/v1
kind: Deployment
metadata:
  name: postgres
spec:
  replicas: 1
  selector:
    matchLabels:
      app: postgres
  template:
    metadata:
      labels:
        app: postgres  
    spec:
      containers:
      - name: postgres
        image: postgres:12.4-alpine
        ports:
          - containerPort: 5432
        envFrom:
          - secretRef:
              name: postgres-secrets
          - configMapRef:
              name: postgres-configmap  
        volumeMounts:
        - name: postgres-database-storage
          mountPath: /var/lib/pgsql/data
      volumes:
      - name: postgres-database-storage
        persistentVolumeClaim:
          claimName: postgres-pv-claim

Exposing PostgreSQL

Services running in Kubernetes are exposed using Kubernetes Services. The following Service manifest will attach to our Postgres deployment and accept traffic over TCP port 5432.

apiVersion: v1
kind: Service
metadata:
  name: postgres
spec:
  selector:
    app: postgress
  ports:
  - protocol: TCP
    port: 5432
  clusterIP: none

In the manifest above we’ve chosen not to provide an internal Cluster IP address to our Postgres service. We do not want the service to be exposed outside of the cluster. Rather, we want to force applications to connect to this service using Kubernetes’ CoreDNS.

The DNS name for this service will be the following.

postres.default.svc

The default part of the name is derived from the resource’s namespace. Since we have not set a namespace for our Postgre reources, they will automaticaly default to the default namespace.

Backing up Databases

As with any database service, backups should be done routinely in order to safe guard your data. While you could kubectl exec into the running Postgres Pod and run the pg_dump, that’s a manual process that should be avoided.

Instead, we are going to create a CronJob in order for us to automate the task. A Kuberentes CronJob is a scheduled job that schedules a pod for executing commands. Our CronJob will perform the following tasks.

  • Use the Google Cloud SDK Docker image
  • Mount the Postgre database persistent volume.
  • Use the Postgres ConfigMap and Secret to inject environment variables
  • Execute pg_dump against the database
  • Copy the database dump to a Google Cloud Storage Bucket.
apiVersion: batch/v1beta1
kind: CronJob
metadata:
  name: postgres-backup
spec:
  schedule: "*/1 * * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: postgres-backup
            image: google/cloud-sdk:alpine
            args:
            - apk --update add postgresql
            - pg_dump -u myblog > myblog-$(date +%s).bak
            - gsutil cp myblog.bak gs://myblog/backups
            envFrom:
            - secretRef:
                name: postres-secrets
            - configMapRef:
                name: postgres-configmap
            volumeMounts:
            - name: postgres-database-storage
              mountPath: /var/lib/pgsql/data
          volumes:
          - name: postgres-database-storage
            persistentVolumeClaim:
              claimName: postgres-pv-claim         

Upgrading PostgreSQL on Kubernetes

New versions of Postgres our released on a regular basis, from major releases to bug\security fixes. While our database service is running in a containerized world, swapping your image from an older release to a newer one will likely not work.

Major and Minor Upgrades

When major new release of PostgreSQL is released databases on your current release must be upgraded to the latest schema. This is a hard requirement, and that makes it impossible to do in a containerized workload.

For major releases you will need to do the following:

  1. Create a separate deployment running a more recent container image of PostgreSQL.
  2. Dump your data from the currently running pod.
  3. Import your data dump into the newer PostgreSQL deployment.
  4. Tear down your old PostgreSQL deployment.

For a more detailed workflow for upgrading PostgreSQL running in Kubernetes, read How to upgrade PostgreSQL in Docker and Kubernetes

Bug fixes

Bugfix and security patches do not have the same requirement as major and minor PostgreSQL releases. You can simply update your deployment to the latest bugfix version (X.X.1 -> X.X.2).

Author Photo
Blogger, Developer, pipeline builder, cloud engineer, and DevSecOps specialist. I have been working in the cloud for over a decade and running containized workloads since 2012, with gigs at small startups to large financial enterprises.

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