Docker overview

OS-level virtualization

Note: This document is marp compatible.

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Intro

Similar technologies existed for decades:

• zones (Solaris 10, February 2004)
• jails (FreeBSD 4.0, March 2000)
• chroot (Unix v7, 1979)
• user access separation (multics, unix, early 1970s)

Most Linux required features existed since 2.6
Docker reuses existing standards/technologies/philosophy.

• That’s it? What’s the catch?

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Ecosystem

• comprehensive documentation
  • https://docs.docker.com/
• distinct interface:
  • CLI: docker, podman
  • clouds
• registries (hubs):
  • public: docker.io, quay.io, registry.fedoraproject.org
  • self-hosted
  • localhost cache

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Terminology

• image (ls ~/.local/share/containers/storage/overlay/)
• container
• hub (https://hub.docker.com/search?type=image)
• volume

https://docs.docker.com/glossary/

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Under the hood

• runC universal runtime
  • split: kernel namespaces (net/pid/mount/user/networks…) (2002)
  • limit: cgroups (2007)
  • chroot (pivot root)
  • …
• OverlayFS (layers)

https://www.codementor.io/blog/docker-technology-5x1kilcbow

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Key takeaway

• NO kernel inside
• SINGLE process (although it may fork kids inside the same container)

From wikimedia –>

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Hands on

docker search <name>
docker pull <NAME[:TAG|@DIGEST]>
docker run -it --rm -p <host_port>:<docker_port> -v <image> [cmd]

docker run -d <image>
docker attach

docker stop
docker start
docker log

Example: docker run -p 8080:8888 -it --rm bash nc -l -p 8888

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Dockerfile

Refer: https://docs.docker.com/develop/develop-images/dockerfile_best-practices/ Doc: https://docs.docker.com/engine/reference/builder/

Notable keywords
FROM	LABEL	USER
RUN	COPY/ADD	EXPOSE
ENV	(ENTRYPOINT)	CMD

Example: ubuntu dockerfile

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Quick build and share image

docker image build --rm -t test_image <path-to-dockerfile>
docker image save test_image -o test.tar
...
docker image load -i test.tar

Consider using multi-stage builds.

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Exploring and housekeeping

docker info | less

docker history --no-trunc <imgname>
docker image inspect <imgname>

docker image ls
docker image rm <image_name>
docker image prune

docker container ps -a
docker container rm <container_id>
docker container prune