Kubernetes Service for a Subset of StatefulSet Pods

Question

I have a StatefulSet with 3 pods. The first is assigned to the master role, the rest have a read replica role.

redis-0 (master)
redis-1 (replica)
redis-2 (replica)

How can I create a Kubernetes Service that matches only the pods redis-1 and redis-2? Basically I want to service that points only to the pods acting as replicas?

Logically what I want is to select every pod in the STS except the first. In pseudocode:

selector: app=redis-sts && statefulset.kubernetes.io/pod-name!=redis-0

Alternatively, selecting all the relevant pods could be viable. Again in psuedocode:

selector: statefulset.kubernetes.io/pod-name=redis-1 || statefulset.kubernetes.io/pod-name=redis-2

Here is the relevant YAML with the selectors & service defined. Full YAML.

apiVersion: v1
kind: Service
metadata:
  name: redis-service
spec:
  ports:
  - port: 6379
  clusterIP: None
  selector:
    app: redis-sts
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: redis
spec:
  selector:
    matchLabels:
      app: redis-sts
  serviceName: redis-service
  replicas: 3
  template:
    metadata:
      labels:
        app: redis-sts
    spec:
# ...

Rakesh Gupta Rakesh Gupta · Accepted Answer · 2021-06-25T02:47:10

You may use pod name labels of your redis statefulset to create the service to access a particular read replica pod.

apiVersion: v1
kind: Service
metadata:
  name: redis-1
spec:
  type: LoadBalancer
  externalTrafficPolicy: Local
  selector:
    statefulset.kubernetes.io/pod-name: redis-1
  ports:
  - protocol: TCP
    port: 6379
    targetPort: 6379

And then use the service name for the pod to access the specific pods.

externalTrafficPolicy: Local will only proxy the traffic to the node that has the instance of your pod.

Kubernetes Service for a Subset of StatefulSet Pods

3 Answers