Why interacting with containers matters in Docker - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why do we need to interact with running containers?

Which of the following best explains why interacting with running containers is important in DevOps?

A To monitor and debug applications inside containers in real time.

B To permanently change the container image stored in the registry.

C To increase the container size for more storage automatically.

D To convert containers into virtual machines for better performance.

💡 Hint

Think about what you might do if an app inside a container is not working as expected.

Interacting with running containers allows you to check logs, run commands, and fix issues without rebuilding images. This helps in quick debugging and monitoring.

💻 Command Output

intermediate

Output of docker exec command

What will be the output of the following command if the container named webapp is running and has a file /app/version.txt containing 'v1.2.3'?

Docker

docker exec webapp cat /app/version.txt

A v1.2.3

B Error: No such file or directory

C Container webapp not found

D Permission denied

💡 Hint

Consider what docker exec does when running a command inside a container.

The docker exec command runs the given command inside the specified running container. If the file exists, it outputs its content.

🔀 Workflow

advanced

Correct sequence to interact with a container shell

What is the correct order of commands to start a container named db if stopped, then open an interactive shell inside it?

A 1,3,2,4

B 3,1,2,4

C 1,2,3,4

D 3,2,1,4

💡 Hint

Think about checking container status before starting and interacting.

First, check running containers with docker ps. Then start the container if stopped. Next, open an interactive shell. Stopping is optional and last.

❓ Troubleshoot

advanced

Why does docker exec fail with 'No such container'?

You run docker exec myapp ls but get the error 'Error: No such container: myapp'. What is the most likely cause?

A You do not have permission to run docker commands.

B The 'ls' command is not installed inside the container.

C The container named 'myapp' is not running or does not exist.

D Docker daemon is not running on the host machine.

💡 Hint

Consider what the error message says about the container name.

The error means Docker cannot find a running container with the name 'myapp'. The container might be stopped or never created.

✅ Best Practice

expert

Best practice for persistent data when interacting with containers

Which option describes the best practice to keep data safe and persistent when interacting with containers that may be stopped or removed?

A Copy data to a temporary folder inside the container before stopping it.

B Save data inside the container’s writable layer and commit changes to the image.

C Rely on container snapshots to restore data after removal.

D Use Docker volumes or bind mounts to store data outside the container filesystem.

💡 Hint

Think about how container filesystems behave when containers are deleted.

Container filesystems are ephemeral. Using volumes or bind mounts stores data outside containers, ensuring persistence even if containers are removed.