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In-Class Exercise - Docker Commit Workflow

  • Start an alpine container and keep it running for modifications
  • Create a new file inside the running container
  • Use docker commit to capture a new image with the file included
  • Run a container from the committed image and verify the file exists
  • Hint: Combine docker run, docker exec, docker commit, and docker run --rm
Solution

Step-by-Step Solution

  1. Run a modifiable alpine container
docker run -d --name alpine-commit alpine:latest sleep infinity
  1. Write a file inside the running container
docker exec alpine-commit sh -c "echo 'Persisted with docker commit' > /opt/commit-note.txt"
  1. Validate the file inside the original container (optional check)
docker exec alpine-commit cat /opt/commit-note.txt
  1. Create a new image from the modified container
docker commit alpine-commit alpine-with-note:latest
  1. Run a container from the committed image and verify the file exists
docker run --rm alpine-with-note:latest cat /opt/commit-note.txt

Expected output:

Persisted with docker commit
  1. Clean up resources
docker rm -f alpine-commit
docker image rm alpine-with-note:latest

Explanation

  • docker run -d … sleep infinity: Starts a container that stays alive for edits
  • docker exec … echo ‘…’ > file: Writes a file into the running container
  • docker commit: Captures the container’s filesystem changes into a new image
  • docker run –rm new-image cat file: Launches the new image, verifies the persistent file, and removes the container when done
  • Cleanup commands: Remove the temporary container and image to free resources