Implementing and Configuring Liveness and Readiness Probes in Kubernetes

Overview

Liveness and readiness probes are crucial for maintaining the health and efficiency of applications in Kubernetes, implemented using HTTP requests or command executions within the container.

Documentation

Configure Liveness, Readiness and Startup Probes.

Implementing HTTP Get Probes

Liveness Probe with HTTP Get

Ensures the nginx container is alive. Restarts the container upon probe failure.
```
livenessProbe:
  httpGet:
    path: /
    port: 80
  initialDelaySeconds: 3
  periodSeconds: 3
```
HTTP Get Probes Documentation.

Readiness Probe with HTTP Get

Assesses if the container is ready to accept traffic.

readinessProbe:
  httpGet:
    path: /
    port: 80
  initialDelaySeconds: 15
  periodSeconds: 5

Readiness Probes Documentation.

Implementing Command-Based Probes

Command-based probes are another method to determine container status:

Liveness Probe with Command

Executes a command inside the container, restarting it upon failure.

livenessProbe:
  exec:
    command:
    - cat
    - /tmp/healthy
  initialDelaySeconds: 15
  periodSeconds: 20

Command Probes Documentation.

Readiness Probe with Command

Checks container readiness through a command execution.

readinessProbe:
  exec:
    command:
    - cat
    - /tmp/ready
  initialDelaySeconds: 5
  periodSeconds: 10

Command Probes Documentation.

Example Pod Configuration

Here's an example of a Pod using both HTTP Get and Command probes:

apiVersion: v1
kind: Pod
metadata:
  name: probe-pod
spec:
  containers:
  - name: nginx-container
    image: nginx:1.20.1
    ports:
    - containerPort: 80
    livenessProbe:
      httpGet:
        path: /
        port: 80
      initialDelaySeconds: 3
      periodSeconds: 3
    readinessProbe:
      exec:
        command:
        - cat
        - /usr/share/nginx/html/index.html
      initialDelaySeconds: 5
      periodSeconds: 10

In this configuration, the nginx container employs an HTTP Get liveness probe and a command-based readiness probe verifying the index.html file's presence.

Conclusion

Effectively utilizing liveness and readiness probes in Kubernetes is vital for ensuring applications run correctly and are prepared for traffic. These probes enable Kubernetes to manage containers based on real-time status, boosting application reliability and availability.