Container health checks in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the Dockerfile line to add a health check that runs the command 'curl -f http://localhost/'

Docker

HEALTHCHECK CMD [1]

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

Acurl -f http://localhost/

Becho 'healthy'

Cls /app

Dping -c 1 localhost

Attempts:

3 left

💡 Hint

Common Mistakes

Using commands that do not test the service health like 'ls' or 'echo'.

Using ping which may not be installed or meaningful inside the container.

The HEALTHCHECK CMD instruction runs the specified command inside the container to check its health. Using curl -f http://localhost/ checks if the web service is responding.

2fill in blank

medium

Complete the Docker Compose service definition to add a health check that retries every 10 seconds

Docker

healthcheck:
  test: [1]
  interval: 10s

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

A["CMD", "curl", "-f", "http://localhost/"]

Bcurl -f http://localhost/

C"curl -f http://localhost/"

D["RUN", "curl", "-f", "http://localhost/"]

Attempts:

3 left

💡 Hint

Common Mistakes

Using plain strings instead of arrays for the test command.

Using RUN instead of CMD in the test array.

In Docker Compose, the healthcheck test must be an array starting with CMD to run the command properly.

3fill in blank

hard

Fix the error in this Dockerfile health check line to correctly specify the command

Docker

HEALTHCHECK CMD [1]

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

A["RUN", "curl", "-f", "http://localhost/"]

Bcurl -f http://localhost/

C["curl", "-f", "http://localhost/"]

Dcurl http://localhost/

Attempts:

3 left

💡 Hint

Common Mistakes

Using plain strings instead of JSON arrays.

Using RUN in the command array.

The health check command must be specified as a JSON array starting with the executable and its arguments. Using ["curl", "-f", "http://localhost/"] is correct.

4fill in blank

hard

Fill both blanks to create a health check in Docker Compose that retries every 5 seconds and fails after 3 retries

Docker

healthcheck:
  test: [1]
  interval: 5s
  retries: [2]

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

A["CMD", "curl", "-f", "http://localhost/"]

B10s

C3

Dcurl -f http://localhost/

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string instead of an array for the test command.

Setting retries to a string like '3' instead of a number.

The test must be a command array starting with CMD. The retries option sets how many times Docker retries before marking unhealthy.

5fill in blank

hard

Fill all three blanks to define a Dockerfile health check with a 30-second timeout, 10-second interval, and 5 retries

Docker

HEALTHCHECK --timeout=[1] --interval=[2] --retries=[3] CMD curl -f http://localhost/

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

A30s

B10s

C5

D60s

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up timeout and interval values.

Using strings instead of numbers for retries.

The --timeout sets how long to wait for the health check command, --interval sets how often to run it, and --retries sets how many failures before marking unhealthy.