Workloads: Deployments, StatefulSets, DaemonSets

Kubernetes provides several workload controllers for running containers in a GKE cluster. Each controller is designed for a specific type of application. Understanding when to use each one is fundamental to building reliable applications on GKE.

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Deployments

A Deployment is the most common workload controller. It manages a set of identical, stateless pods and handles rolling updates, rollbacks, and scaling. Deployments are the right choice for stateless applications such as web servers, APIs, and microservices.

Key Features

Feature	Description
Rolling updates	New pods are gradually created while old pods are terminated
Rollback	Revert to any previous revision
Scaling	Scale up or down by changing the replica count
Self-healing	Failed pods are automatically replaced
ReplicaSet	A Deployment manages a ReplicaSet, which manages pods

Example Deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-api
  labels:
    app: web-api
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web-api
  template:
    metadata:
      labels:
        app: web-api
    spec:
      containers:
        - name: web-api
          image: europe-west2-docker.pkg.dev/my-project/repo/web-api:v1.2.0
          ports:
            - containerPort: 8080
          resources:
            requests:
              cpu: 250m
              memory: 256Mi
            limits:
              cpu: 500m
              memory: 512Mi
          livenessProbe:
            httpGet:
              path: /healthz
              port: 8080
            initialDelaySeconds: 5
            periodSeconds: 10
          readinessProbe:
            httpGet:
              path: /ready
              port: 8080
            initialDelaySeconds: 5
            periodSeconds: 5

Rolling Update Strategy

spec:
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1        # 1 extra pod during update
      maxUnavailable: 0   # No pods unavailable during update (zero-downtime)

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StatefulSets

StatefulSets manage stateful applications that require stable network identities, persistent storage, and ordered deployment. They are used for databases, message queues, and distributed systems like ZooKeeper, Kafka, and Elasticsearch.

Key Features

Feature	Description
Stable pod names	Pods are named sequentially (my-app-0, my-app-1, my-app-2)
Stable network identity	Each pod gets a DNS name via a Headless Service
Persistent storage	Each pod gets its own PersistentVolumeClaim that persists across restarts
Ordered operations	Pods are created, updated, and deleted in order
Ordered scaling	Scale-up creates pods sequentially; scale-down removes them in reverse order

Example StatefulSet