Building images with docker build - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this Docker build command?

You run the command docker build -t myapp:latest . in a directory with a valid Dockerfile. What will be the result?

A Docker will build the image but tag it as 'latest' without the 'myapp' name.

B Docker builds the image and tags it as 'myapp:latest' if successful.

C Docker builds the image but does not tag it because the '-t' flag is ignored.

D Docker will throw an error because the tag format is incorrect.

💡 Hint

The '-t' flag is used to name and tag the image during build.

The command 'docker build -t myapp:latest .' builds the Docker image from the current directory and tags it with the name 'myapp' and tag 'latest'. This is the standard way to name images during build.

💻 Command Output

intermediate

What error does this Docker build command produce?

You run docker build -f Dockerfile.dev . but the file 'Dockerfile.dev' does not exist in the directory. What error will Docker show?

A Permission denied error accessing Dockerfile.dev

B Syntax error in Dockerfile.dev

C Build completes successfully using default Dockerfile

D Error response from daemon: Dockerfile not found: Dockerfile.dev

💡 Hint

The '-f' flag specifies a Dockerfile name. If missing, Docker uses 'Dockerfile'.

Docker looks for the file specified by '-f'. If it does not exist, it returns an error saying the Dockerfile was not found.

🔀 Workflow

advanced

Which option correctly builds a Docker image using a specific Dockerfile and no cache?

You want to build an image named 'webapp:1.0' using the Dockerfile named 'Dockerfile.prod' and ensure no cache is used during build. Which command is correct?

A docker build -t webapp:1.0 -f Dockerfile.prod --no-cache .

B docker build --no-cache -t webapp:1.0 Dockerfile.prod

C docker build -f Dockerfile.prod -t webapp:1.0 . --no-cache

D docker build -t webapp:1.0 . -f Dockerfile.prod --no-cache

💡 Hint

The order of flags matters; the context path must be last.

The correct syntax places the '-f' and '--no-cache' flags before the context path '.' and specifies the tag with '-t'. Option A follows this syntax exactly.

❓ Troubleshoot

advanced

Why does this Docker build command fail with a syntax error?

You run docker build -t myimage . -f Dockerfile and get a syntax error. What is the cause?

A Dockerfile name is case sensitive and 'Dockerfile' is incorrect

B The tag '-t' must be after the context path '.'

C The '-f' flag must come before the context path '.'

D The context path '.' must be omitted when using '-f'

💡 Hint

Flags must appear before the context path in the command.

Docker expects all flags before the context path. Placing '-f Dockerfile' after '.' causes Docker to treat it as a build context, leading to an error.

✅ Best Practice

expert

What is the best practice to reduce image size when building with Docker?

You want to build a small Docker image for production. Which practice below helps reduce the final image size?

A Use multi-stage builds to copy only necessary artifacts into the final image

B Use the 'latest' tag to always get the newest base image

C Install all build tools inside the final image for debugging

D Avoid specifying a base image to keep the image minimal

💡 Hint

Multi-stage builds separate build environment from runtime environment.

Multi-stage builds allow you to compile or build your app in one stage and copy only the needed files to a smaller final image, reducing size and attack surface.