StatefulSet YAML

The StatefulSet YAML is similar to a Deployment's; additionally, serviceName is required. It's the name of the headless service that gives the pods DNS records:

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: db
spec:
  serviceName: db
  replicas: 3
  selector:
    matchLabels:
      app: db
  template:
    metadata:
      labels:
        app: db
    spec:
      containers:
        - name: postgres
          image: postgres:16
          ports:
            - containerPort: 5432

A service with clusterIP: None gets no virtual IP; a DNS query returns the pod IPs directly and each StatefulSet pod gets its own record in the form pod-name.service-name. That way clients can connect to a specific replica (e.g. the primary):

apiVersion: v1
kind: Service
metadata:
  name: db
spec:
  clusterIP: None
  selector:
    app: db
  ports:
    - port: 5432

# db-0.db.default.svc.cluster.local -> 10.244.1.12
# db-1.db.default.svc.cluster.local -> 10.244.2.15