Why understanding lifecycle matters in Docker - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the command to start a Docker container in detached mode.

Docker

docker run -d [1] nginx

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

A--rm

B-it

C-p 80:80

D-v /data:/data

Attempts:

3 left

💡 Hint

Common Mistakes

Using -it starts an interactive terminal, not detached mode.

Forgetting to map ports means the service won't be reachable.

The -p 80:80 option maps port 80 of the container to port 80 on the host, allowing web traffic. This is important when starting a web server container like nginx.

2fill in blank

medium

Complete the command to list all Docker containers, including stopped ones.

Docker

docker ps [1]

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

A-q

B--filter

C-l

D-a

Attempts:

3 left

💡 Hint

Common Mistakes

Using -q only shows container IDs.

Using -l shows only the last created container.

The -a option shows all containers, including those that are stopped. Without it, only running containers are listed.

3fill in blank

hard

Fix the error in the command to remove a stopped container named 'webapp'.

Docker

docker [1] webapp

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

Astop

Brm

Crun

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using stop only stops the container but does not remove it.

Using run tries to start a new container.

The rm command removes a container. You must stop it first if it is running. Here, the container is stopped, so docker rm webapp deletes it.

4fill in blank

hard

Fill both blanks to create a Dockerfile line that copies files and sets the working directory.

Docker

COPY [1] /app/
WORKDIR [2]

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

A.

B/app

C/usr/src/app

Dsrc

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong source path for COPY causes missing files.

Setting WORKDIR to a different folder than copied files causes confusion.

The COPY . /app/ copies all files from the current folder to /app in the container. Then WORKDIR /app sets the working directory inside the container to /app.

5fill in blank

hard

Fill all three blanks to write a Docker command that builds an image named 'myapp' from the current directory.

Docker

docker build [1] -t [2] [3]

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

A--no-cache

Bmyapp

C.

D-f Dockerfile

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the build context '.' causes errors.

Forgetting to tag the image results in an untagged image.

The -f Dockerfile option specifies the Dockerfile to use. The -t myapp tags the image with the name 'myapp'. The . tells Docker to use the current directory as the build context.

Practice

1. Why is it important to understand the lifecycle of a Docker container?

easy

A. To improve the speed of the Docker installation process

B. To write complex Dockerfiles with many layers

C. To manage when containers start, stop, and get removed efficiently

D. To avoid using Docker Compose files

Solution

1. Step 1: Understand container lifecycle basics

   The lifecycle includes starting, running, stopping, and removing containers.

2. Step 2: Connect lifecycle to resource management

   Managing lifecycle properly helps keep the environment clean and avoids wasting resources.

3. Final Answer:

   To manage when containers start, stop, and get removed efficiently -> Option C

4. Quick Check:

   Lifecycle management = efficient container control [OK]

Hint: Lifecycle means start, stop, remove containers properly [OK]

Common Mistakes:

• Confusing lifecycle with Dockerfile writing
• Thinking lifecycle affects installation speed
• Believing lifecycle avoids using Compose files

2. Which Docker command correctly stops a running container named webapp?

easy

A. docker stop webapp

B. docker remove webapp

C. docker start webapp

D. docker run webapp

Solution

1. Step 1: Identify command to stop containers

   The docker stop command stops a running container gracefully.

2. Step 2: Check other commands' purposes

   docker rm deletes containers, docker start starts stopped containers, docker run creates and starts new containers.

3. Final Answer:

   docker stop webapp -> Option A

4. Quick Check:

   Stop command = docker stop [OK]

Hint: Stop containers with 'docker stop <container>' [OK]

Common Mistakes:

• Using 'docker remove' to stop containers
• Confusing 'docker start' with stopping
• Trying 'docker run' to stop containers

3. What will be the output of the following commands?

docker run --name test1 alpine echo Hello
docker ps -a --filter "name=test1" --format "{{.Status}}"

medium

A. Up 5 seconds

B. Error: No such container

C. Created

D. Exited (0) X seconds ago

Solution

1. Step 1: Understand 'docker run' with echo

   The container runs the command 'echo Hello' and then exits immediately after printing.

2. Step 2: Check container status with 'docker ps -a'

   The container is stopped but exists, so status shows 'Exited (0) X seconds ago'.

3. Final Answer:

   Exited (0) X seconds ago -> Option D

4. Quick Check:

   Run echo container exits immediately = Exited status [OK]

Hint: Containers running short commands exit quickly showing 'Exited' [OK]

Common Mistakes:

• Expecting 'Up' status after short command
• Thinking container is still 'Created' but not running
• Assuming container is deleted automatically

4. You ran docker rm mycontainer but got an error saying the container is running. What should you do to fix this?

medium

A. Run docker rm mycontainer -f to force remove

B. Run docker stop mycontainer before removing

C. Restart Docker service and try again

D. Rename the container and then remove it

Solution

1. Step 1: Understand why removal failed

   Docker won't remove running containers without stopping them first.

2. Step 2: Proper fix is to stop container before removal

   Use docker stop mycontainer to stop it, then remove safely.

3. Final Answer:

   Run docker stop mycontainer before removing -> Option B

4. Quick Check:

   Stop container before remove = docker stop then rm [OK]

Hint: Stop container before removing it to avoid errors [OK]

Common Mistakes:

• Forcing removal without stopping can cause issues
• Restarting Docker service won't fix running container
• Renaming container doesn't affect removal

5. You want to ensure a container automatically removes itself after it stops to keep your system clean. Which Docker run option should you use?

hard

A. --rm

B. -d

C. --restart always

D. -it

Solution

1. Step 1: Identify option for auto-removal

   The --rm flag tells Docker to remove the container after it stops.

2. Step 2: Understand other options

   -d runs detached, --restart always restarts container on failure, -it runs interactively.

3. Final Answer:

   --rm -> Option A

4. Quick Check:

   Auto-remove container = --rm flag [OK]

Hint: Use --rm to auto-remove stopped containers [OK]

Common Mistakes:

• Using -d to remove containers automatically
• Confusing restart policies with removal
• Thinking -it affects container lifecycle removal