Why probes keep applications healthy in Kubernetes - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a liveness probe that checks the application health on port 8080.

Kubernetes

livenessProbe:
  httpGet:
    path: /healthz
    port: [1]

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

A8080

B80

C443

D3000

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong port number causes the probe to fail.

The liveness probe uses port 8080 to check the health endpoint /healthz.

2fill in blank

medium

Complete the code to set a readiness probe that checks the path '/ready' on port 9090.

Kubernetes

readinessProbe:
  httpGet:
    path: [1]
    port: 9090

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

A/healthz

B/status

C/ready

D/live

Attempts:

3 left

💡 Hint

Common Mistakes

Using the liveness path instead of readiness path.

The readiness probe checks the /ready path to confirm the app is ready to receive traffic.

3fill in blank

hard

Fix the error in the probe configuration by choosing the correct probe type.

Kubernetes

[1]:
  exec:
    command:
    - cat
    - /tmp/healthy

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

AreadinessProbe

BlivenessProbe

ChttpGet

DtcpSocket

Attempts:

3 left

💡 Hint

Common Mistakes

Using httpGet or tcpSocket keys incorrectly.

The probe type must be livenessProbe to check if the container is alive using an exec command.

4fill in blank

hard

Fill both blanks to create a readiness probe with a TCP socket check on port 3306.

Kubernetes

readinessProbe:
  [1]:
    port: [2]

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

AtcpSocket

BhttpGet

C3306

D8080

Attempts:

3 left

💡 Hint

Common Mistakes

Using HTTP probe type with a port number for TCP check.

The readiness probe uses a TCP socket check on port 3306 to verify the app is ready.

5fill in blank

hard

Fill all three blanks to define a liveness probe that runs a command, with initial delay and timeout seconds.

Kubernetes

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

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

Acat

B/tmp/healthy

C5

Dcurl

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong command or missing initial delay.

The liveness probe runs cat /tmp/healthy command with an initial delay of 5 seconds.

Practice

1. What is the main purpose of a liveness probe in Kubernetes?

easy

A. To check if the application is running and restart it if it is not healthy

B. To control when the application receives user traffic

C. To update the application configuration automatically

D. To monitor the CPU usage of the application

Solution

1. Step 1: Understand liveness probe role

   Liveness probes check if the app is alive and working properly.

2. Step 2: Identify action on failure

   If the liveness probe fails, Kubernetes restarts the app to fix it.

3. Final Answer:

   To check if the application is running and restart it if it is not healthy -> Option A

4. Quick Check:

   Liveness probe = restarts unhealthy app [OK]

Hint: Liveness probe restarts app if unhealthy [OK]

Common Mistakes:

• Confusing liveness with readiness probe
• Thinking liveness controls traffic
• Assuming liveness updates configs

2. Which of the following is the correct syntax to define a readiness probe in a Kubernetes pod spec?

easy

A. readinessProbe:
httpGet:
path: /ready
port: 8080
initialDelaySeconds: 5
periodSeconds: 10

B. livenessProbe:
exec:
command: ["curl", "/health"]
timeoutSeconds: 3

C. readinessProbe:
tcpSocket:
port: 80
failureThreshold: 5

D. startupProbe:
httpGet:
path: /start
port: 9090
periodSeconds: 15

Solution

1. Step 1: Identify readiness probe syntax

   Readiness probes often use httpGet with path and port defined.

2. Step 2: Match correct YAML structure

   readinessProbe: httpGet: path: /ready port: 8080 initialDelaySeconds: 5 periodSeconds: 10 shows readinessProbe with httpGet, initialDelaySeconds, and periodSeconds correctly.

3. Final Answer:

   readinessProbe: httpGet: path: /ready port: 8080 initialDelaySeconds: 5 periodSeconds: 10 -> Option A

4. Quick Check:

   Readiness probe syntax = readinessProbe: httpGet: path: /ready port: 8080 initialDelaySeconds: 5 periodSeconds: 10 [OK]

Hint: Readiness probe uses httpGet with path and port [OK]

Common Mistakes:

• Mixing liveness and readiness probe syntax
• Using startupProbe instead of readinessProbe
• Incorrect indentation or missing fields

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

readinessProbe:
  httpGet:
    path: /healthz
    port: 8080
  initialDelaySeconds: 5
  periodSeconds: 10

medium

A. The pod is restarted immediately

B. The pod stops receiving new traffic but keeps running

C. The pod is deleted from the cluster

D. Nothing happens; the pod continues as normal

Solution

1. Step 1: Understand readiness probe effect

   Readiness probe controls if pod is ready to get user traffic.

2. Step 2: Identify behavior on failure

   If readiness probe fails, pod stays running but is removed from service endpoints, so no new traffic.

3. Final Answer:

   The pod stops receiving new traffic but keeps running -> Option B

4. Quick Check:

   Readiness failure = no traffic, pod runs [OK]

Hint: Readiness failure stops traffic, no restart [OK]

Common Mistakes:

• Thinking readiness failure restarts pod
• Confusing readiness with liveness probe
• Assuming pod deletion on readiness failure

4. You notice your application pod keeps restarting frequently. The liveness probe is defined as:

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

What is the most likely cause?

medium

A. The readiness probe is missing

B. The liveness probe is incorrectly configured with wrong port

C. The pod has insufficient CPU resources

D. The application is not responding to the /health endpoint in time

Solution

1. Step 1: Analyze liveness probe behavior

   Liveness probe checks /health on port 8080 every 10 seconds after 5 seconds delay.

2. Step 2: Understand restart cause

   If app does not respond correctly 3 times (failureThreshold), Kubernetes restarts pod.

3. Final Answer:

   The application is not responding to the /health endpoint in time -> Option D

4. Quick Check:

   Liveness failure = app not responding, causes restart [OK]

Hint: Liveness failure causes restart due to no response [OK]

Common Mistakes:

• Assuming readiness probe causes restart
• Ignoring failureThreshold effect
• Blaming resource limits without evidence

5. You want to ensure your app only receives traffic after it finishes loading data and is ready. Which probe setup achieves this best?

hard

A. Use a startup probe that immediately sends traffic to the app

B. Use a liveness probe that restarts the app if /health fails

C. Use a readiness probe that checks a /ready endpoint returning success after data load

D. Use both liveness and readiness probes checking the same /health endpoint

Solution

1. Step 1: Identify probe controlling traffic

   Readiness probe controls when app receives user traffic.

2. Step 2: Choose probe matching app readiness

   Readiness probe checking /ready after data load ensures traffic only after app is ready.

3. Step 3: Exclude other options

   Liveness restarts app but does not control traffic; startup probe delays startup but not traffic control.

4. Final Answer:

   Use a readiness probe that checks a /ready endpoint returning success after data load -> Option C

5. Quick Check:

   Readiness probe controls traffic flow [OK]

Hint: Readiness probe controls traffic after app is ready [OK]

Common Mistakes:

• Using liveness probe to control traffic
• Confusing startup probe with readiness probe
• Checking same endpoint for both probes