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In-Class Exercise - Multi-Stage Dockerfile

  • Create a multi-stage docker file that will build 2 images
  • The first image will be based on alpine and will create a file named alpine.txt with the content: This is alpine image
  • The second image will be based on node and will create a file named node.txt with the content: This is node image
  • The final image should be based on alpine and should copy the files which you created from the previous stages and display their content when the container will run.
  • Hint: Use the COPY --from= command to copy files from previous stages
Solution

Dockerfile Solution

Create a file named Dockerfile-exercise:

# First stage: Alpine image
FROM  alpine AS alpine-stage
RUN   echo "This is alpine image" > alpine.txt

# Second stage: Node image
FROM  node AS node-stage
RUN   echo "This is node image" > node.txt

# Final stage: Alpine with files from previous stages
FROM  alpine
COPY  --from=alpine-stage alpine.txt  .
COPY  --from=node-stage node.txt      .

# Run the command to display contents
CMD   cat alpine.txt && cat node.txt

Build and Test

Build the image:

docker build -f Dockerfile-exercise -t exercise-solution .

Run the container:

docker run exercise-solution

Expected output:

This is alpine image
This is node image

Explanation

  1. First Stage (alpine-stage): Based on alpine, creates alpine.txt with the required content
  2. Second Stage (node-stage): Based on node, creates node.txt with the required content
  3. Final Stage: Based on alpine (lightweight), copies both files from previous stages using COPY --from=<stage-name> and displays their content when run