Pod-to-Pod communication in Kubernetes - Commands & Configuration

Introduction

Pods in Kubernetes are groups of containers that share network and storage. Pod-to-Pod communication means letting these pods talk to each other inside the cluster. This helps apps work together smoothly.

When you want a frontend pod to get data from a backend pod inside the cluster

When multiple pods need to share information or coordinate tasks

When you want to test if two pods can connect before deploying a full app

When you want to expose a pod's service to other pods without external access

When you want to debug network issues between pods

Config File - pod-communication.yaml

pod-communication.yaml

apiVersion: v1
kind: Pod
metadata:
  name: pod-a
  labels:
    app: pod-a
spec:
  containers:
  - name: container-a
    image: busybox
    command: ["sleep", "3600"]
    ports:
    - containerPort: 80
---
apiVersion: v1
kind: Pod
metadata:
  name: pod-b
  labels:
    app: pod-b
spec:
  containers:
  - name: container-b
    image: busybox
    command: ["sleep", "3600"]
    ports:
    - containerPort: 80
---
apiVersion: v1
kind: Service
metadata:
  name: pod-b-service
spec:
  selector:
    app: pod-b
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80
  type: ClusterIP

This file creates two pods named pod-a and pod-b, each running a simple container that sleeps to stay alive. It also creates a Service named pod-b-service that selects pod-b by its label. This service gives pod-b a stable network name and IP inside the cluster, so pod-a can reach it easily.

Commands

This command creates the two pods and the service in the Kubernetes cluster. It sets up the environment for pod-to-pod communication.

Terminal

kubectl apply -f pod-communication.yaml

Expected Output

pod/pod-a created

pod/pod-b created

service/pod-b-service created

This command checks that both pods are running and ready to communicate.

Terminal

kubectl get pods

Expected Output

NAME    READY   STATUS    RESTARTS   AGE

pod-a   1/1     Running   0          10s

pod-b   1/1     Running   0          10s

This command runs a simple HTTP request from pod-a to pod-b using the service name. It tests if pod-a can reach pod-b inside the cluster.

Terminal

kubectl exec pod-a -- wget -qO- http://pod-b-service

Expected Output

No output (command runs silently)

→

-- - Separates kubectl exec options from the command to run inside the pod

This command shows details about the service that connects to pod-b, including its cluster IP and ports.

Terminal

kubectl describe service pod-b-service

Expected Output

Name:              pod-b-service

Namespace:         default

Labels:            <none>

Annotations:       <none>

Selector:          app=pod-b

Type:              ClusterIP

IP:                10.96.0.1

Port:              80/TCP

TargetPort:        80/TCP

Endpoints:         10.244.1.5:80

Session Affinity:  None

Events:            <none>

Key Concept

Pods can communicate inside a Kubernetes cluster using Services that provide stable network names and IPs.

Common Mistakes

Trying to connect to a pod directly by its IP address

Pod IPs can change when pods restart, so connections break.

Use a Service to give pods a stable network name and IP.

Not labeling pods correctly to match the Service selector

The Service won't find the pods to route traffic to, so communication fails.

Make sure pod labels match the Service selector exactly.

Running commands without the '--' flag in kubectl exec

kubectl treats the command as its own option, causing errors.

Always use '--' before the command to run inside the pod.

Summary

Create pods and a Service to enable stable network communication between pods.

Use kubectl exec with the '--' flag to run commands inside pods for testing connectivity.

Verify pods are running and the Service is correctly routing traffic.