Why interacting with containers matters in Docker - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the command to list all running Docker containers.

Docker

docker [1]

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

Arun

Bstart

Cbuild

Dps

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'docker run' instead of 'docker ps' to list containers.

The docker ps command shows all running containers.

2fill in blank

medium

Complete the command to start an existing container named 'webapp'.

Docker

docker [1] webapp

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

Abuild

Bstop

Cstart

Drm

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'docker run' which creates a new container instead of starting an existing one.

The docker start command starts a stopped container.

3fill in blank

hard

Fix the error in the command to open an interactive shell inside a running container named 'db'.

Docker

docker exec -it [1] /bin/bash

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

Abash

Bdb

Crun

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'bash' or 'run' instead of the container name.

The container name or ID must be specified after docker exec -it.

4fill in blank

hard

Fill both blanks to run a new container from the 'nginx' image and map port 8080 on the host to port 80 in the container.

Docker

docker run -d -p [1]:[2] nginx

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

A8080

B80

C443

D3000

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the ports or using unrelated ports like 443 or 3000.

Port 8080 on the host maps to port 80 inside the container where nginx listens.

5fill in blank

hard

Fill all three blanks to create a Docker volume named 'data_vol', mount it to '/data' inside a container, and run the container from the 'busybox' image.

Docker

docker volume [1] data_vol && docker run -v data_vol:[2] [3] busybox

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

Acreate

B/data

C-it

Drm

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'rm' instead of 'create' to make the volume.

Wrong mount path or missing interactive flag.

You create a volume with docker volume create, mount it to /data, and run interactively with -it.

Practice

1. Why is it important to interact with a running Docker container?

easy

A. To check the container's current status and logs

B. To delete the container permanently

C. To create a new Docker image

D. To install Docker on the host machine

Solution

1. Step 1: Understand container interaction purpose

   Interacting with a running container helps monitor its status and troubleshoot issues.

2. Step 2: Identify correct interaction use

   Checking logs and status is a common reason to interact, unlike deleting or installing Docker.

3. Final Answer:

   To check the container's current status and logs -> Option A

4. Quick Check:

   Container interaction = status check [OK]

Hint: Interacting means checking or controlling running containers [OK]

Common Mistakes:

• Confusing interaction with image creation
• Thinking interaction means deleting containers
• Mixing up Docker installation with container interaction

2. Which of the following commands correctly attaches to a running Docker container named webapp?

easy

A. docker start webapp

B. docker run webapp

C. docker attach webapp

D. docker build webapp

Solution

1. Step 1: Identify command to interact with running container

   The docker attach command connects your terminal to a running container.

2. Step 2: Differentiate from other commands

   docker run starts a new container, docker start starts a stopped container, and docker build creates an image.

3. Final Answer:

   docker attach webapp -> Option C

4. Quick Check:

   Attach = connect to running container [OK]

Hint: Attach connects terminal to running container [OK]

Common Mistakes:

• Using 'docker run' to connect to running container
• Confusing 'docker start' with attaching
• Mixing build command with container interaction

3. What will be the output of the command docker logs mycontainer if the container is running a web server that just started successfully?

medium

A. Error: No such container: mycontainer

B. Server started on port 80

C. Container stopped unexpectedly

D. Usage: docker logs [OPTIONS] CONTAINER

Solution

1. Step 1: Understand purpose of docker logs

   This command shows the output logs of the specified container.

2. Step 2: Predict expected log output

   If the container runs a web server that started successfully, logs will show a startup message like 'Server started on port 80'.

3. Final Answer:

   Server started on port 80 -> Option B

4. Quick Check:

   Logs show container output = startup message [OK]

Hint: Logs show what container prints during run [OK]

Common Mistakes:

• Expecting error when container exists
• Confusing usage message with logs
• Assuming container stopped when running

4. You tried to attach to a container using docker attach myapp but got no response. What is the most likely reason?

medium

A. The container is not running

B. You misspelled the command

C. Docker daemon is not installed

D. The container image is missing

Solution

1. Step 1: Understand docker attach requirements

   This command only works if the container is currently running.

2. Step 2: Analyze possible causes for no response

   If the container is stopped, attach will not connect and appear unresponsive.

3. Final Answer:

   The container is not running -> Option A

4. Quick Check:

   Attach needs running container [OK]

Hint: Attach only works on running containers [OK]

Common Mistakes:

• Assuming command typo without checking container state
• Thinking Docker daemon missing causes attach failure
• Confusing image presence with container running

5. You want to interactively debug a container named dbserver that is running but not responding correctly. Which sequence of commands lets you start a new shell session inside it without stopping the container?

hard

A. docker attach dbserver && exit

B. docker stop dbserver && docker run -it dbserver /bin/bash

C. docker build -t debug dbserver

D. docker exec -it dbserver /bin/bash

Solution

1. Step 1: Identify command to open shell in running container

   docker exec -it runs a new interactive shell inside the running container without stopping it.

2. Step 2: Eliminate incorrect options

   Stopping container loses state, attach connects to main process, build creates image not shell.

3. Final Answer:

   docker exec -it dbserver /bin/bash -> Option D

4. Quick Check:

   Exec runs shell inside running container [OK]

Hint: Use exec -it to open shell inside running container [OK]

Common Mistakes:

• Stopping container before debugging loses state
• Using attach instead of exec for shell access
• Confusing build with container interaction