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Posted on May 16 • Originally published at dingjiu1989-hue.github.io

Databases in Containers: StatefulSets, Persistent Volumes, and Backup

#database #backend #data

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Databases in Containers: StatefulSets, Persistent Volumes, and Backup

Running databases in containers was once considered an anti-pattern, but modern orchestration and storage primitives have made it viable for many production workloads. This article covers Kubernetes patterns for stateful databases, storage management, and operational considerations.

StatefulSets vs Deployments

Kubernetes Deployments are designed for stateless applications. StatefulSets are the correct primitive for databases:

apiVersion: apps/v1

kind: StatefulSet

metadata:

spec:

serviceName: postgres

replicas: 3

selector:

matchLabels:

app: postgres

template:

metadata:

labels:

app: postgres

spec:

containers:

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\- name: postgres

image: postgres:16

ports:

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\- containerPort: 5432

env:

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\- name: POSTGRES_PASSWORD

valueFrom:

secretKeyRef:

key: password

volumeMounts:

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\- name: data

mountPath: /var/lib/postgresql/data

volumeClaimTemplates:

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\- metadata:

spec:

accessModes: [ "ReadWriteOnce" ]

storageClassName: "fast-ssd"

resources:

requests:

storage: 100Gi

StatefulSets provide:

Stable, unique network identities (pod-name-0, pod-name-1).
Ordered, graceful deployment and scaling.
Stable storage with PersistentVolumeClaim templates.

PersistentVolumes and Storage Classes

Database storage requires careful configuration of PersistentVolumes:

apiVersion: storage.k8s.io/v1

kind: StorageClass

metadata:

provisioner: ebs.csi.aws.com

parameters:

type: gp3

iops: "3000"

throughput: "125"

reclaimPolicy: Retain

Access Modes

| Mode | Description | Database Use Case | |------|-------------|-------------------| | ReadWriteOnce | Single node read-write | Primary database | | ReadOnlyMany | Many nodes read-only | Read replicas | | ReadWriteMany | Many nodes read-write | Shared storage (avoid for PostgreSQL) |

CloudNativePG Operator

The CloudNativePG operator is the most mature Kubernetes operator for PostgreSQL:

apiVersion: postgresql.cnpg.io/v1

kind: Cluster

metadata:

spec:

instances: 3

imageName: ghcr.io/cloudnative-pg/postgresql:16

storage:

size: 100Gi

storageClass: fast-ssd

backup:

barmanObjectStore:

destinationPath: s3://myapp-backups/

s3Credentials:

accessKeyId:

key: access-key

secretAccessKey:

key: secret-key

wal:

compression: gzip

retentionPolicy: "30d"

monitoring:

enablePodMonitor: true

resources:

requests:

memory: "4Gi"

cpu: "2"

limits:

memory: "8Gi"

cpu: "4"

Automated Failover

Simulate pod failure to test failover

kubectl delete pod myapp-db-0

Operator automatically:

1\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

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Databases in Containers: StatefulSets, Persistent Volumes, and Backup

Databases in Containers: StatefulSets, Persistent Volumes, and Backup