Tagging images during build in Docker - 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:1.0 . in a directory with a valid Dockerfile. What will be the tag of the built image?

Docker

docker build -t myapp:1.0 .

A The image will be tagged as 'myapp:latest'.

B The image will be tagged as 'latest'.

C The image will be tagged as 'myapp:1.0'.

D The image will have no tag.

💡 Hint

The -t option sets the tag explicitly.

Using -t with 'myapp:1.0' tags the image exactly as 'myapp:1.0'. Without -t, Docker defaults to 'latest'.

❓ Configuration

intermediate

Which Dockerfile instruction sets the image tag during build?

You want to set the image tag inside the Dockerfile itself during build time. Which instruction achieves this?

A LABEL version="1.0"

B There is no Dockerfile instruction to set the image tag; tags are set during the docker build command.

C ENV TAG=1.0

D TAG myapp:1.0

💡 Hint

Think about where tags are applied in Docker workflow.

Docker image tags are assigned during the build command, not inside the Dockerfile. Dockerfile instructions configure the image content, not its tag.

🔀 Workflow

advanced

How to tag the same image with multiple tags during build?

You want to build a Docker image and tag it as both 'myapp:1.0' and 'myapp:latest' in one command. Which command achieves this?

A docker build -t myapp:1.0,latest .

B docker build -tag myapp:1.0 -tag myapp:latest .

C docker build --tag myapp:1.0 --tag myapp:latest .

D docker build -t myapp:1.0 -t myapp:latest .

💡 Hint

Multiple -t options can be used.

Docker build supports multiple -t options to assign multiple tags to the same image in one build.

❓ Troubleshoot

advanced

Why does this Docker build command fail to tag the image?

You run docker build . -t myapp:1.0 but the image is not tagged as expected. What is the problem?

Docker

docker build . -t myapp:1.0

A The -t option must come before the build context '.'

B The tag 'myapp:1.0' is invalid

C Dockerfile is missing in the directory

D The build context '.' is incorrect

💡 Hint

Check the order of options and arguments in the command.

Docker build expects options like -t before the build context argument. Placing -t after '.' causes it to be ignored.

✅ Best Practice

expert

What is the best practice for tagging images in CI/CD pipelines?

In a CI/CD pipeline, you want to tag Docker images to track builds uniquely and also have a stable tag for deployment. Which tagging strategy is best?

A Tag images with the commit SHA and also tag the same image as 'latest' for deployment

B Only tag images as 'latest' to keep it simple

C Tag images with random numbers to avoid collisions

D Tag images with timestamps only

💡 Hint

Consider traceability and stable references.

Using commit SHA tags allows traceability to exact code versions, while 'latest' provides a stable tag for deployment. This is a common best practice.