Health checks in containers in Microservices - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Microservices

livenessProbe:
  httpGet:
    path: [1]
    port: 8080

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

A/ready

B/healthz

C/status

D/metrics

Attempts:

3 left

💡 Hint

Common Mistakes

Using readiness probe endpoints for liveness checks

Using metrics endpoints which are not suitable for liveness

The liveness probe commonly uses the /healthz endpoint to check if the container is alive.

2fill in blank

medium

Complete the code to define a readiness probe command in a Kubernetes pod.

Microservices

readinessProbe:
  exec:
    command: ["[1]", "-c", "curl -f http://localhost:8080/ready || exit 1"]

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

Ash

Bcurl

Cbash

Dwget

Attempts:

3 left

💡 Hint

Common Mistakes

Using curl directly as the command without a shell

Using wget which may not be installed

The readiness probe often uses a shell command like sh to run a curl command inside the container.

3fill in blank

hard

Fix the error in the Kubernetes readiness probe configuration.

Microservices

readinessProbe:
  tcpSocket:
    port: [1]

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

Aready

B80

C8080

Dhttp

Attempts:

3 left

💡 Hint

Common Mistakes

Using protocol names instead of port numbers

Using endpoint paths in tcpSocket probes

The tcpSocket probe requires a port number, not a string or protocol name.

4fill in blank

hard

Fill both blanks to create a Kubernetes liveness probe that checks an HTTP endpoint after a 10 second initial delay.

Microservices

livenessProbe:
  httpGet:
    path: [1]
    port: 8080
  initialDelaySeconds: [2]

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

A/healthz

B5

C10

D/ready

Attempts:

3 left

💡 Hint

Common Mistakes

Using readiness paths for liveness probes

Setting initial delay too low causing false failures

The liveness probe should check the /healthz path and start after 10 seconds delay.

5fill in blank

hard

Fill in the blank to define a readiness probe with an exec command that retries curl 3 times.

Microservices

readinessProbe:
  exec:
    command: ["[1]", "-c", "for i in {1..3}; do curl -f http://localhost:8080/ready && exit 0 || sleep 1; done; exit 1"]

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

Adash

Bsh

Czsh

Dbash

Attempts:

3 left

💡 Hint

Common Mistakes

Using shells that do not support brace expansion

Using shells not installed in the container

The bash shell supports the for loop syntax used in the command.

Practice

1. What is the main purpose of health checks in containers?

easy

A. To log all container network traffic

B. To increase the container's memory allocation

C. To update the container's software automatically

D. To verify if the container is running and responsive

Solution

1. Step 1: Understand container health checks

   Health checks are used to confirm if a container is alive and working properly.

2. Step 2: Identify the main goal

   The main goal is to detect if the container is responsive and healthy, so it can be restarted if needed.

3. Final Answer:

   To verify if the container is running and responsive -> Option D

4. Quick Check:

   Health checks = verify container health [OK]

Hint: Health checks confirm container responsiveness [OK]

Common Mistakes:

• Confusing health checks with resource allocation
• Thinking health checks update software
• Assuming health checks log network data

2. Which of the following is the correct syntax to define a simple HTTP health check in a Docker container?

easy

A. HEALTHCHECK EXECUTE curl -f http://localhost/

B. HEALTHCHECK RUN curl http://localhost/

C. HEALTHCHECK CMD curl -f http://localhost/ || exit 1

D. HEALTHCHECK CHECK curl http://localhost/

Solution

1. Step 1: Recall Docker health check syntax

   The correct Dockerfile syntax uses HEALTHCHECK CMD followed by a command that returns 0 on success.

2. Step 2: Identify the correct command

   HEALTHCHECK CMD curl -f http://localhost/ || exit 1 uses 'curl -f' which fails on HTTP errors and 'exit 1' on failure, matching best practice.

3. Final Answer:

   HEALTHCHECK CMD curl -f http://localhost/ || exit 1 -> Option C

4. Quick Check:

   Docker healthcheck syntax = HEALTHCHECK CMD [OK]

Hint: Docker healthchecks use 'HEALTHCHECK CMD' syntax [OK]

Common Mistakes:

• Using RUN instead of CMD in HEALTHCHECK
• Using EXECUTE or CHECK which are invalid keywords
• Not handling failure with exit codes

3. Consider this Kubernetes liveness probe configuration snippet:

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

What happens if the container's /health endpoint returns HTTP 500 continuously?

medium

A. Kubernetes restarts the container after failing the liveness probe

B. Kubernetes ignores the failure and keeps the container running

C. Kubernetes scales up the number of containers

D. Kubernetes shuts down the entire pod immediately

Solution

1. Step 1: Understand liveness probe behavior

   Liveness probes check if a container is alive; failure triggers a restart of that container.

2. Step 2: Analyze the HTTP 500 response effect

   HTTP 500 means the endpoint is unhealthy, so Kubernetes marks the probe as failed and restarts the container.

3. Final Answer:

   Kubernetes restarts the container after failing the liveness probe -> Option A

4. Quick Check:

   Liveness probe failure = container restart [OK]

Hint: Liveness failure triggers container restart [OK]

Common Mistakes:

• Thinking Kubernetes ignores liveness failures
• Confusing liveness probe with scaling behavior
• Assuming pod shutdown instead of container restart

4. You have this Dockerfile snippet:

HEALTHCHECK CMD curl -f http://localhost:5000/health || exit 1

But the container never restarts even when the service is down. What is the likely issue?

medium

A. The container restart policy is not set to restart on failure

B. The container does not expose port 5000

C. The health check command is missing the --interval option

D. The HEALTHCHECK CMD syntax is incorrect

Solution

1. Step 1: Check health check command correctness

   The command syntax is correct and uses curl -f with exit 1 on failure.

2. Step 2: Consider container restart policy

   If the container restart policy is not set to restart on failure, the container won't restart despite health check failures.

3. Final Answer:

   The container restart policy is not set to restart on failure -> Option A

4. Quick Check:

   Restart policy controls container restart on health failure [OK]

Hint: Check restart policy if container doesn't restart [OK]

Common Mistakes:

• Assuming health check command syntax is wrong
• Ignoring restart policy settings
• Thinking missing --interval causes no restart

5. You want to design a microservice container that uses both readiness and liveness probes. Which of the following best describes their combined use?

hard

A. Both probes only log health status without affecting container state

B. Liveness probe restarts unhealthy containers; readiness probe controls traffic routing to only ready containers

C. Both probes restart containers on failure

D. Readiness probe restarts containers; liveness probe controls traffic routing

Solution

1. Step 1: Understand liveness probe role

   Liveness probes detect if a container is alive; failure triggers container restart.

2. Step 2: Understand readiness probe role

   Readiness probes check if a container is ready to serve traffic; failure removes it from load balancer routing.

3. Step 3: Combine their functions

   Liveness restarts unhealthy containers; readiness controls traffic flow to only healthy containers.

4. Final Answer:

   Liveness probe restarts unhealthy containers; readiness probe controls traffic routing to only ready containers -> Option B

5. Quick Check:

   Liveness = restart, Readiness = traffic control [OK]

Hint: Liveness restarts; readiness controls traffic [OK]

Common Mistakes:

• Mixing up readiness and liveness roles
• Thinking readiness probe restarts containers
• Assuming probes only log status without action