Probe failure and container restart behavior in Kubernetes - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the liveness probe command in a Kubernetes pod spec.

Kubernetes

livenessProbe:
  exec:
    command:
    - [1]

Drag options to blanks, or click blank then click option'

Acurl

Bcat

Cls

Decho

Attempts:

3 left

💡 Hint

Common Mistakes

Using commands that do not check service health like 'ls' or 'cat'.

The liveness probe uses curl to check if the container is alive by making an HTTP request.

2fill in blank

medium

Complete the code to set the initial delay before the liveness probe starts.

Kubernetes

livenessProbe:
  initialDelaySeconds: [1]

Drag options to blanks, or click blank then click option'

A10

B300

C60

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Setting delay too low causing premature probe failures.

The initialDelaySeconds is set to 10 seconds to give the container time to start before probing.

3fill in blank

hard

Fix the error in the restart policy to ensure the container restarts on failure.

Kubernetes

restartPolicy: [1]

Drag options to blanks, or click blank then click option'

ASometimes

BAlways

CNever

DOnFailure

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Never' which disables restarts, or 'Always' which restarts even on success.

The OnFailure restart policy restarts the container only if it fails, which is typical for probe failure handling.

4fill in blank

hard

Fill both blanks to configure readiness and liveness probes with HTTP GET method.

Kubernetes

readinessProbe:
  httpGet:
    path: [1]
    port: [2]
livenessProbe:
  httpGet:
    path: /healthz
    port: 8080

Drag options to blanks, or click blank then click option'

A/ready

B80

C8080

D/status

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong paths or mismatched ports causing probe failures.

The readiness probe checks /ready on port 8080, matching the liveness probe port.

5fill in blank

hard

Fill all three blanks to create a liveness probe with exec command, initial delay, and failure threshold.

Kubernetes

livenessProbe:
  exec:
    command:
    - [1]
  initialDelaySeconds: [2]
  failureThreshold: [3]

Drag options to blanks, or click blank then click option'

Apgrep

B15

C3

Dcurl

Attempts:

3 left

💡 Hint

Common Mistakes

Using HTTP commands in exec probe or setting too low failure threshold.

The probe uses pgrep to check a process, waits 15 seconds before starting, and allows 3 failures before restart.

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