Debugging service connectivity in Kubernetes - Commands & Configuration

Introduction

Sometimes your app cannot talk to another app inside Kubernetes. Debugging service connectivity helps find why the connection fails and fix it quickly.

When your frontend app cannot reach the backend service inside the cluster.

When a pod cannot connect to a database service running in Kubernetes.

When you want to check if a service is exposing the right ports and endpoints.

When network policies might be blocking traffic between pods.

When you want to verify DNS resolution of service names inside the cluster.

Commands

Check which pods are running to confirm your app and service pods are up.

Terminal

kubectl get pods

Expected Output

NAME                        READY   STATUS    RESTARTS   AGE

frontend-5d8f7c9d7f-abc12  1/1     Running   0          10m

backend-6f7d8c9d7f-def34   1/1     Running   0          10m

List services to verify the backend service is created and exposing the correct ports.

Terminal

kubectl get svc

Expected Output

NAME       TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)    AGE

backend    ClusterIP   10.96.123.45    <none>        8080/TCP   10m

kubernetes ClusterIP   10.96.0.1       <none>        443/TCP    1d

From the frontend pod, try to connect to the backend service using curl to test connectivity.

Terminal

kubectl exec frontend-5d8f7c9d7f-abc12 -- curl -sS backend:8080

Expected Output

Hello from backend!

→

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

Show detailed info about the backend service to check endpoints and ports.

Terminal

kubectl describe svc backend

Expected Output

Name:              backend

Namespace:         default

Labels:            <none>

Annotations:       <none>

Selector:          app=backend

Type:              ClusterIP

IP:                10.96.123.45

Port:              8080/TCP

Endpoints:         10.244.1.5:8080

Session Affinity:  None

Events:            <none>

Check the IP addresses of pods behind the backend service to ensure they are ready.

Terminal

kubectl get endpoints backend

Expected Output

NAME      ENDPOINTS         AGE

backend   10.244.1.5:8080   10m

Key Concept

If you remember nothing else from this pattern, remember: test connectivity from inside the pod using service names and verify service endpoints.

Common Mistakes

Trying to curl the service from outside the cluster without port forwarding or ingress.

Services of type ClusterIP are only reachable inside the cluster, so external curl will fail.

Use kubectl exec to run curl inside a pod or use port forwarding to access the service externally.

Assuming the service IP is the pod IP and trying to connect directly to pod IPs.

Pods can change IPs and are not stable endpoints; services provide stable access.

Always use the service name or ClusterIP to connect to pods.

Not checking if the backend pods are ready before testing connectivity.

If pods are not ready or crashed, the service will have no endpoints and connections fail.

Use kubectl get pods and kubectl describe pods to confirm pod readiness.

Summary

Check pods and services to confirm your apps are running and exposed.

Use kubectl exec with curl inside a pod to test service connectivity by name and port.

Describe the service and check endpoints to verify backend pods are correctly linked.