Exec probe configuration in Kubernetes - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an exec probe in Kubernetes?

An exec probe runs a command inside a container to check if the container is healthy. If the command succeeds, the container is considered healthy.

beginner

Which Kubernetes probe type uses a command to check container health?

The exec probe type uses a command executed inside the container to check its health.

intermediate

How do you define an exec probe in a Pod YAML file?

You define an exec probe under the livenessProbe or readinessProbe section with a command list under exec, like:

livenessProbe:
  exec:
    command: ["/bin/check.sh"]
  initialDelaySeconds: 5
  periodSeconds: 10

beginner

What happens if the exec probe command fails?

If the exec probe command returns a non-zero exit code, Kubernetes considers the container unhealthy and may restart it depending on the probe type.

intermediate

Why use exec probes instead of HTTP or TCP probes?

Exec probes allow custom health checks by running any command inside the container, useful when HTTP or TCP checks are not applicable.

What does an exec probe do in Kubernetes?

A Runs a command inside the container to check health

B Sends an HTTP request to the container

C Checks if a TCP port is open

D Monitors container CPU usage

Exec probes run a command inside the container to determine health.

Where do you specify the exec command in a Kubernetes probe?

A Under env: variables: in container spec

B Under httpGet: path: in livenessProbe

C Under exec: command: in livenessProbe or readinessProbe

D Under tcpSocket: port: in readinessProbe

The exec command is specified under exec: command: in the probe section.

What exit code from an exec probe command means the container is healthy?

A 1

B 0

C Any non-zero code

D 255

Exit code 0 means success and healthy container.

If an exec probe fails repeatedly, what does Kubernetes do?

A Restarts the container

B Ignores the failure

C Deletes the Pod immediately

D Scales the deployment up

Kubernetes restarts the container if the liveness exec probe fails repeatedly.

Which probe type is best when you need to run a custom script inside the container?

A TCP probe

B HTTP probe

C None of the above

D Exec probe

Exec probes allow running custom scripts or commands inside the container.

Explain how to configure an exec probe in a Kubernetes Pod YAML file.

Think about where the exec command goes and timing settings.

Describe what happens when an exec probe command fails in Kubernetes.

Focus on exit codes and Kubernetes reaction.

Practice

1. What is the main purpose of an exec probe in Kubernetes?

easy

A. To schedule pods on specific nodes

B. To expose container ports to the outside world

C. To create persistent storage volumes

D. To run a command inside a container to check if it is healthy

Solution

1. Step 1: Understand exec probe functionality

   An exec probe runs a command inside the container to check its health status.

2. Step 2: Compare with other options

   Options A, B, and D relate to scheduling, networking, and storage, not health checks.

3. Final Answer:

   To run a command inside a container to check if it is healthy -> Option D

4. Quick Check:

   Exec probe = runs command inside container [OK]

Hint: Exec probe runs commands inside container to check health [OK]

Common Mistakes:

• Confusing exec probe with port exposure
• Thinking exec probe schedules pods
• Mixing exec probe with storage management

2. Which of the following is the correct syntax snippet to define an exec liveness probe in a pod spec?

easy

A. livenessProbe:\n exec:\n command: ['cat', '/tmp/healthy']\n initialDelaySeconds: 5\n periodSeconds: 10

B. livenessProbe:\n httpGet:\n path: /healthz\n port: 8080\n initialDelaySeconds: 5

C. livenessProbe:\n exec:\n command: 'cat /tmp/healthy'\n initialDelaySeconds: 5

D. livenessProbe:\n exec:\n command: cat /tmp/healthy\n initialDelaySeconds: 5

Solution

1. Step 1: Check exec command format

   The command must be an array of strings, e.g., ['cat', '/tmp/healthy'].

2. Step 2: Validate YAML structure

   livenessProbe:\n exec:\n command: ['cat', '/tmp/healthy']\n initialDelaySeconds: 5\n periodSeconds: 10 correctly uses the array syntax and includes initialDelaySeconds and periodSeconds.

3. Final Answer:

   Correct exec probe with command array and delays -> Option A

4. Quick Check:

   Exec command = array of strings [OK]

Hint: Exec command must be a list of strings in YAML [OK]

Common Mistakes:

• Using a single string instead of array for command
• Confusing exec probe with httpGet probe
• Omitting required indentation or keys

3. Given this exec probe configuration in a pod spec:

livenessProbe:
  exec:
    command: ['test', '-f', '/tmp/healthy']
  initialDelaySeconds: 3
  periodSeconds: 5

What happens if the file /tmp/healthy does not exist inside the container?

medium

A. The probe ignores the missing file and logs a warning

B. The probe passes and container continues running

C. The probe fails and Kubernetes restarts the container after retries

D. The container is immediately deleted without restart

Solution

1. Step 1: Understand exec probe command

   The command 'test -f /tmp/healthy' returns success if the file exists, failure if not.

2. Step 2: Effect of probe failure

   If the probe fails repeatedly, Kubernetes restarts the container to recover.

3. Final Answer:

   The probe fails and Kubernetes restarts the container after retries -> Option C

4. Quick Check:

   Missing file = probe fails = restart [OK]

Hint: Missing file causes exec probe failure and container restart [OK]

Common Mistakes:

• Assuming probe passes if file missing
• Thinking container deletes without restart
• Believing probe ignores errors silently

4. You configured an exec readiness probe but your pod never becomes ready. Which of these is the most likely cause?

medium

A. The exec command is missing the command array syntax and uses a single string

B. The initialDelaySeconds is set too high

C. The container image is missing

D. The pod has no resource limits defined

Solution

1. Step 1: Check exec command syntax

   Exec probe commands must be an array of strings; a single string causes probe failure.

2. Step 2: Understand probe failure effect

   If the probe fails, the pod is not marked ready, so it never becomes ready.

3. Final Answer:

   Exec command missing array syntax causes probe failure -> Option A

4. Quick Check:

   Exec command array syntax missing = probe fails [OK]

Hint: Exec command must be array; single string causes failure [OK]

Common Mistakes:

• Ignoring command array syntax errors
• Blaming initialDelaySeconds without checking command
• Confusing readiness with resource limits

5. You want to configure an exec liveness probe that waits 10 seconds before starting, runs the command ['/bin/check.sh'], retries every 5 seconds, and fails after 3 unsuccessful attempts. Which is the correct YAML snippet?

hard

A. livenessProbe:\n exec:\n command: '/bin/check.sh'\n initialDelaySeconds: 10\n periodSeconds: 5\n failureThreshold: 3

B. livenessProbe:\n exec:\n command: ['/bin/check.sh']\n initialDelaySeconds: 10\n periodSeconds: 5\n failureThreshold: 3

C. livenessProbe:\n exec:\n command: ['/bin/check.sh']\n initialDelaySeconds: 5\n periodSeconds: 10\n failureThreshold: 3

D. livenessProbe:\n exec:\n command: ['/bin/check.sh']\n initialDelaySeconds: 10\n periodSeconds: 5\n failureThreshold: 1

Solution

1. Step 1: Verify command syntax and initial delay

   Command must be an array; initialDelaySeconds must be 10 as required.

2. Step 2: Check periodSeconds and failureThreshold

   PeriodSeconds should be 5 for retry every 5 seconds; failureThreshold 3 means fail after 3 tries.

3. Final Answer:

   Correct YAML with command array, initialDelaySeconds 10, periodSeconds 5, failureThreshold 3 -> Option B

4. Quick Check:

   Command array + delays + failureThreshold correct = livenessProbe:\n exec:\n command: ['/bin/check.sh']\n initialDelaySeconds: 10\n periodSeconds: 5\n failureThreshold: 3 [OK]

Hint: Use array for command and set delays and failureThreshold as numbers [OK]

Common Mistakes:

• Using string instead of array for command
• Swapping periodSeconds and initialDelaySeconds values
• Setting failureThreshold too low or missing