Why probes keep applications healthy in Kubernetes - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Purpose of Kubernetes Readiness Probe

What is the main purpose of a readiness probe in Kubernetes?

A To monitor the CPU and memory usage of the pod

B To restart the container if it crashes or becomes unresponsive

C To check if the application is ready to receive traffic and only then add it to the service endpoints

D To update the container image automatically when a new version is available

💡 Hint

Think about when Kubernetes should send traffic to a pod.

The readiness probe tells Kubernetes if the pod is ready to accept traffic. If the probe fails, Kubernetes stops sending requests to that pod until it passes again.

💻 Command Output

intermediate

Output of a Failing Liveness Probe

Given the following liveness probe configuration, what will Kubernetes do if the probe fails repeatedly?

Kubernetes

livenessProbe:
  httpGet:
    path: /healthz
    port: 8080
  initialDelaySeconds: 5
  periodSeconds: 10
  failureThreshold: 3

A Kubernetes will delete the pod permanently

B Kubernetes will stop sending traffic to the pod but will not restart it

C Kubernetes will ignore the failures and keep the container running

D Kubernetes will restart the container after 3 consecutive failures of the probe

💡 Hint

Remember what a liveness probe is designed to do.

The liveness probe checks if the container is alive. If it fails the configured number of times, Kubernetes restarts the container to try to fix the problem.

🔀 Workflow

advanced

Order of Probe Checks in Kubernetes

Arrange the following Kubernetes probe checks in the order they are typically performed during pod lifecycle:

A 1,2,3,4

B 2,1,4,3

C 2,3,1,4

D 3,2,1,4

💡 Hint

Think about what happens first when a pod starts and how traffic is routed.

The startup probe runs first to check if the app has started. Then readiness probe checks if it can receive traffic. If ready, pod is added to endpoints. Liveness probe runs continuously to check if app is alive.

❓ Troubleshoot

advanced

Troubleshooting a Pod Not Receiving Traffic

A pod is running but not receiving any traffic. The readiness probe is configured but the pod never becomes ready. What is the most likely cause?

A The readiness probe is failing, so Kubernetes does not add the pod to service endpoints

B The liveness probe is failing, causing the pod to restart repeatedly

C The pod has insufficient CPU resources and is throttled

D The container image is outdated and incompatible with the cluster

💡 Hint

Focus on what controls traffic routing to pods.

If the readiness probe fails, Kubernetes considers the pod not ready and excludes it from the service endpoints, so it won't receive traffic.

✅ Best Practice

expert

Best Practice for Using Startup Probes

Why is it recommended to use a startup probe for applications with long initialization times?

A To prevent Kubernetes from killing the container prematurely before it finishes starting

B To speed up the pod startup by skipping readiness checks

C To automatically scale the number of pods based on startup time

D To disable liveness and readiness probes during startup

💡 Hint

Think about what happens if liveness probes run too early on slow-starting apps.

Startup probes allow Kubernetes to wait longer for the app to start before running liveness probes. This avoids killing the container too soon.