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Docker: images and containers

Image, container, registry, tag and daemon; the commands pull, run (-d, -p, -e, --name, --rm), ps, stop, start, rm, logs, exec, images and rmi; container states and port publishing.

  • 30 cards
  • 6 topics
  • Free
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Each topic is weighted the way the exam weighs it.

  1. Concepts
  2. Questions
  3. Sort and link
  4. The steps
  5. Scenarios
  6. Understand

A few cards from the deck

  • Docker image: what is it?

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    A read-only template, built in layers, from which containers are created.

    As many containers as wanted can be created from one image: it never changes, each container adds its own writable layer.

  • Which command starts nginx in the background, named web, reachable on the host's port 8080?

    • docker run -d --name web -p 8080:80 nginx
    • docker run -d --name web -p 80:8080 nginx
    • docker run -d --name web -e 8080:80 nginx
    • docker run --rm --name web -p 8080:80 nginx
    Show the answer

    docker run -d --name web -p 8080:80 nginx

    -d detaches, --name names, -p host:container publishes. nginx listens on 80 inside the container, hence 8080:80. The variant without -d keeps the terminal busy, and -e sets an environment variable, not a port.

  • With -p 8080:80, port … of the host is forwarded to port … of the container.

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    With -p 8080:80, port 8080 of the host is forwarded to port 80 of the container.

    The order is always host then container. -p 80:8080 would do the opposite: open the host's port 80 towards a container listening on 8080.

  • Docker container: what is it?

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    A running instance of an image: an isolated process with a writable layer of its own, deleted only along with the container.

    Image and container are much like a class and an object: the template, then its instances.

  • A container's life cycle: which step comes after "docker create --name web nginx → the container exists, state created"?

    • docker start web → state running
    • docker pause web → state paused
    • docker unpause web → back to state running
    • docker stop web → state exited
    Show the answer

    docker start web → state running

    A container goes through created, running (or paused) then exited, and is only erased by docker rm. docker run chains create and start.

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