Question: How can you achieve high availability for PostgreSQL in Kubernetes?

Answer

Achieving high availability (HA) for PostgreSQL within a Kubernetes environment involves configuring your setup to handle failures gracefully and ensure minimal downtime. Here's a comprehensive guide on how to approach this:

1. Use a Reliable Operator

The first step is to use a Kubernetes operator tailored for PostgreSQL. Operators automate tasks such as deployment, backups, upgrades, and scaling. For PostgreSQL, the Zalando Postgres Operator and Crunchy Data PostgreSQL Operator are popular choices, providing robust tools to manage clusters.

2. Replication Setup

Set up PostgreSQL with one primary node and multiple replica nodes. Replicas will handle read traffic and serve as failovers if the primary goes down. Synchronous replication can be used for zero data loss, although it may impact performance due to the wait for transaction confirmation from replicas.

apiVersion: "acid.zalan.do/v1"
kind: postgresql
metadata:
  name: acid-minimal-cluster
spec:
  teamId: "acid"
  volume:
    size: 1Gi
  numberOfInstances: 3
  users:
    zalando:  # database owner
      - superuser
      - createdb
  databases:
    foo: zalando  # dbname: owner
  preparedDatabases:
    bar: {}
  postgresql:
    version: "13"

3. Persistent Storage

Ensure that your PostgreSQL instances use persistent storage to safeguard data against pod failures. Kubernetes Persistent Volumes (PVs) backed by reliable storage classes (such as those provided by AWS EBS, Google Persistent Disk, or Azure Disk) ensure data durability.

4. Automated Failover

Configure automated failover mechanisms. This could involve using the aforementioned operators which detect failed primary nodes and promote a replica to take over without manual intervention. Proper readiness and liveness probes should also be configured to aid Kubernetes in understanding the state of your PostgreSQL pods.

livenessProbe:
  exec:
    command:
    - sh
    - -c
    - exec pg_isready --host $POD_IP
  initialDelaySeconds: 30
  timeoutSeconds: 5
readinessProbe:
  exec:
    command:
    - sh
    - -c
    - exec pg_isready --host $POD_IP
  initialDelaySeconds: 5
  timeoutSeconds: 5
  periodSeconds: 10
  failureThreshold: 6

5. Monitoring and Alerts

Implement monitoring and alerting tools like Prometheus and Grafana for visibility into the health and performance of your PostgreSQL clusters. Set alerts for critical conditions such as high latency, low disk space, or node unavailability.

6. Regular Backups

Schedule regular backups using tools like pgBackRest or WAL-E, integrated through your chosen operator. These backups should be stored offsite to provide an additional layer of data protection.

By following these guidelines, you can build a resilient PostgreSQL deployment on Kubernetes, ensuring high availability and continuity for your applications.