Readiness probe concept in Kubernetes - Commands & Configuration

Introduction

Sometimes an application inside a container takes time to start and be ready to serve traffic. A readiness probe helps Kubernetes know when the app is ready so it only sends user requests to containers that can handle them.

When your app needs to load data or initialize before it can accept requests

When you want to avoid sending traffic to a container that is still starting up

When you want Kubernetes to automatically stop sending traffic if your app becomes unhealthy

When you want to improve user experience by only routing to ready containers

When you want to manage rolling updates smoothly by checking readiness before switching traffic

Config File - readiness-pod.yaml

readiness-pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: example-readiness-pod
spec:
  containers:
  - name: example-app
    image: nginx:1.23
    readinessProbe:
      httpGet:
        path: /index.html
        port: 80
      initialDelaySeconds: 5
      periodSeconds: 5

This YAML file defines a Pod with one container running nginx.

The readinessProbe uses an HTTP GET request to check if the /index.html page is available on port 80.

initialDelaySeconds waits 5 seconds before the first check to give the app time to start.

periodSeconds sets the probe to run every 5 seconds.

Commands

This command creates the Pod with the readiness probe configured. Kubernetes will start the container and begin checking readiness after the initial delay.

Terminal

kubectl apply -f readiness-pod.yaml

Expected Output

pod/example-readiness-pod created

This command shows the status of the Pod including if it is ready to receive traffic.

Terminal

kubectl get pods example-readiness-pod

Expected Output

NAME                   READY   STATUS    RESTARTS   AGE

example-readiness-pod   1/1     Running   0          10s

This command gives detailed information about the Pod, including readiness probe results and events.

Terminal

kubectl describe pod example-readiness-pod

Expected Output

Name:         example-readiness-pod

Namespace:    default

Status:       Running

Containers:

  example-app:

    Container ID:   docker://abcdef123456

    Image:          nginx:1.23

    Ready:          True

    Restart Count:  0

    Readiness:      http-get http://:80/index.html delay=5s timeout=1s period=5s #success=1 #failure=3

Events:

  Type    Reason     Age   From               Message

  ----    ------     ----  ----               -------

  Normal  Scheduled  1m    default-scheduler  Successfully assigned default/example-readiness-pod to node-1

  Normal  Pulled     1m    kubelet            Container image "nginx:1.23" already present on machine

  Normal  Created    1m    kubelet            Created container example-app

  Normal  Started    1m    kubelet            Started container example-app

Key Concept

If you remember nothing else from this pattern, remember: readiness probes tell Kubernetes when your app is ready to receive traffic, preventing requests from going to containers that are not yet ready.

Common Mistakes

Not setting initialDelaySeconds causing the probe to fail before the app starts

The probe runs too early and marks the container as not ready even though it is just starting up.

Set initialDelaySeconds to a value that gives your app enough time to start before the first probe.

Using a wrong path or port in the readiness probe

The probe will always fail because it cannot reach the correct endpoint, so Kubernetes never marks the container ready.

Verify the path and port in the readiness probe match what your app actually serves.

Confusing readiness probe with liveness probe

Readiness controls traffic routing, liveness controls container restarts; mixing them can cause unexpected restarts or traffic issues.

Use readiness probes to control traffic and liveness probes to check if the container should be restarted.

Summary

Create a Pod with a readiness probe that checks an HTTP endpoint to confirm the app is ready.

Use kubectl apply to create the Pod and kubectl get pods to check if it is ready.

Use kubectl describe pod to see detailed readiness probe results and events.