Probe failure and container restart behavior in Kubernetes - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What happens when a liveness probe fails in Kubernetes?

In Kubernetes, if a liveness probe fails repeatedly, what is the expected behavior for the container?

A The container is restarted by the kubelet.

B The container is paused but not restarted.

C The pod is deleted and recreated by the scheduler.

D Nothing happens; the container continues running.

💡 Hint

Think about how Kubernetes ensures containers stay healthy.

A liveness probe failure signals Kubernetes that the container is unhealthy. Kubernetes restarts the container to try to fix the issue.

💻 Command Output

intermediate

Output of 'kubectl describe pod' after readiness probe failure

You run kubectl describe pod myapp and see the readiness probe failing repeatedly. What status will the pod show in the output?

A Pod status will be <strong>Succeeded</strong>.

B Pod status will be <strong>CrashLoopBackOff</strong>.

C Pod status will be <strong>Pending</strong>.

D Pod status will be <strong>Running</strong> but <em>Ready</em> condition will be <strong>False</strong>.

💡 Hint

Readiness probes affect traffic routing but not pod lifecycle.

When readiness probes fail, the pod stays running but is marked as not ready, so it won't receive traffic.

❓ Troubleshoot

advanced

Why does a container restart repeatedly despite a successful readiness probe?

A container restarts repeatedly, but its readiness probe always succeeds. What is the most likely cause?

A The pod resource limits are too high.

B The readiness probe failure causes restarts.

C The liveness probe is failing, causing restarts.

D The container image is missing.

💡 Hint

Readiness probes do not trigger restarts.

Liveness probe failures cause container restarts. Readiness probes only control traffic routing.

🔀 Workflow

advanced

Order of events when a liveness probe fails repeatedly

Arrange the following Kubernetes events in the correct order when a liveness probe fails repeatedly:

A 2,1,3,4

B 1,2,3,4

C 1,3,2,4

D 3,1,2,4

💡 Hint

Think about how Kubernetes handles unhealthy containers step-by-step.

The kubelet first detects the failure, then kills the container, restarts it, and updates pod status accordingly.

✅ Best Practice

expert

Choosing probe types to avoid unnecessary container restarts

You want to ensure your container restarts only when truly unhealthy, but you also want to control traffic routing carefully. Which probe configuration is best?

A Use a liveness probe that checks critical health and a readiness probe that checks service availability.

B Use only a readiness probe to control restarts and traffic.

C Use only a liveness probe for both restarts and traffic control.

D Disable both probes and rely on manual restarts.

💡 Hint

Consider the distinct roles of liveness and readiness probes.

Liveness probes trigger restarts on failure, readiness probes control traffic routing without restarts. Using both properly avoids unnecessary restarts.

Practice

1. What happens when a Kubernetes liveness probe fails for a container?

easy

A. Traffic to the container is stopped but it is not restarted.

B. The container is restarted by Kubernetes.

C. The container continues running without changes.

D. The container is removed permanently.

Solution

1. Step 1: Understand liveness probe purpose

   Liveness probes check if a container is alive and healthy.

2. Step 2: Effect of liveness probe failure

   If the liveness probe fails, Kubernetes restarts the container to fix the issue.

3. Final Answer:

   The container is restarted by Kubernetes. -> Option B

4. Quick Check:

   Liveness probe failure = container restart [OK]

Hint: Liveness probe failure always triggers container restart [OK]

Common Mistakes:

• Confusing liveness with readiness probe effects
• Thinking container is deleted permanently
• Assuming no action on failure

2. Which of the following is the correct YAML snippet to define a liveness probe using HTTP GET on path /health at port 8080?

easy

A. livenessProbe:
httpGet:
path: health
port: 8080
initialDelaySeconds: 5
periodSeconds: 10

B. livenessProbe:
exec:
command: ["curl", "/health"]
initialDelaySeconds: 5
periodSeconds: 10

C. livenessProbe:
tcpSocket:
port: 8080
initialDelaySeconds: 5
periodSeconds: 10

D. livenessProbe:
httpGet:
path: /health
port: 8080
initialDelaySeconds: 5
periodSeconds: 10

Solution

1. Step 1: Check HTTP GET probe syntax

   The correct syntax uses httpGet with path starting with a slash and port as a number.

2. Step 2: Validate each option

   livenessProbe: httpGet: path: /health port: 8080 initialDelaySeconds: 5 periodSeconds: 10 correctly uses /health and port 8080. livenessProbe: exec: command: ["curl", "/health"] initialDelaySeconds: 5 periodSeconds: 10 uses exec with curl incorrectly. livenessProbe: tcpSocket: port: 8080 initialDelaySeconds: 5 periodSeconds: 10 uses tcpSocket which is different. livenessProbe: httpGet: path: health port: 8080 initialDelaySeconds: 5 periodSeconds: 10 misses the leading slash in path.

3. Final Answer:

   livenessProbe: httpGet: path: /health port: 8080 initialDelaySeconds: 5 periodSeconds: 10 -> Option D

4. Quick Check:

   HTTP GET probe with correct path and port = livenessProbe: httpGet: path: /health port: 8080 initialDelaySeconds: 5 periodSeconds: 10 [OK]

Hint: HTTP path must start with '/' and port is a number [OK]

Common Mistakes:

• Missing leading slash in path
• Using exec command incorrectly
• Confusing tcpSocket with httpGet

3. Given this pod spec snippet, what happens if the readiness probe fails but the liveness probe passes?

readinessProbe:
  httpGet:
    path: /ready
    port: 80
  initialDelaySeconds: 5
  periodSeconds: 10
livenessProbe:
  httpGet:
    path: /live
    port: 80
  initialDelaySeconds: 5
  periodSeconds: 10

medium

A. The container is restarted immediately.

B. The container is deleted and recreated.

C. The container is marked not ready and removed from service endpoints.

D. Nothing happens; container continues serving traffic.

Solution

1. Step 1: Understand readiness probe role

   Readiness probe controls if the container receives traffic by marking it ready or not.

2. Step 2: Effect of readiness probe failure

   If readiness probe fails but liveness probe passes, container stays running but is removed from service endpoints, so no traffic is sent to it.

3. Final Answer:

   The container is marked not ready and removed from service endpoints. -> Option C

4. Quick Check:

   Readiness fail = no traffic, container runs [OK]

Hint: Readiness failure stops traffic, liveness failure restarts container [OK]

Common Mistakes:

• Confusing readiness failure with container restart
• Thinking container is deleted
• Assuming no effect on traffic

4. You notice your container keeps restarting frequently. The liveness probe is configured with initialDelaySeconds: 5 and periodSeconds: 10. What is a likely cause and fix?

medium

A. The initial delay is too short; increase initialDelaySeconds to allow startup time.

B. The period is too long; decrease periodSeconds to check faster.

C. The probe path is incorrect; change it to /healthz.

D. The container image is corrupted; rebuild the image.

Solution

1. Step 1: Analyze probe timing settings

   If initialDelaySeconds is too short, the probe runs before the app is ready, causing false failures.

2. Step 2: Adjust initial delay

   Increasing initialDelaySeconds gives the container time to start before probing, preventing unnecessary restarts.

3. Final Answer:

   The initial delay is too short; increase initialDelaySeconds to allow startup time. -> Option A

4. Quick Check:

   Short initialDelay causes early probe failure [OK]

Hint: Increase initialDelaySeconds if container restarts too soon [OK]

Common Mistakes:

• Changing periodSeconds instead of initialDelaySeconds
• Assuming probe path is always wrong
• Blaming container image without checking probes

5. You have a container with both readiness and liveness probes. The readiness probe fails intermittently, but the liveness probe always passes. How should Kubernetes behave and what is the best way to improve user experience?

hard

A. Kubernetes removes the pod from service during readiness failure but does not restart it; improve by tuning readiness probe thresholds.

B. Kubernetes restarts the container on readiness failure; improve by disabling readiness probe.

C. Kubernetes ignores readiness probe failures if liveness passes; no action needed.

D. Kubernetes deletes the pod on readiness failure; improve by increasing liveness probe timeout.

Solution

1. Step 1: Understand probe roles on intermittent readiness failure

   Readiness failure removes pod from service endpoints but does not restart container if liveness passes.

2. Step 2: Improve user experience by tuning readiness probe

   Tuning thresholds like failureThreshold or periodSeconds reduces false negatives and prevents unnecessary traffic disruption.

3. Final Answer:

   Kubernetes removes the pod from service during readiness failure but does not restart it; improve by tuning readiness probe thresholds. -> Option A

4. Quick Check:

   Readiness fail = no traffic; tune probe to reduce false failures [OK]

Hint: Tune readiness probe to avoid false failures and traffic loss [OK]

Common Mistakes:

• Thinking readiness failure restarts container
• Disabling readiness probe instead of tuning
• Ignoring intermittent failures