2025-01-31 15:38:58 -05:00
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Docker for SW Development
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=========================
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2025-02-02 14:02:10 -05:00
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.. post:: 01, February 2025
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:tags: development, infrastructure, tools, lunch-n-learn
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2025-01-31 15:38:58 -05:00
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:category: Projects
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:author: len0rd
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This is from a lunch-n-learn I hosted which aimed to showcase the features and advantages of using
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docker during the development process. It includes with a few tutorials on how to use it.
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Example code is hosted on my personal git server: https://git.lenord.me/len0rd/docker_demo
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What is Docker
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--------------
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- Framework for defining and running low overhead sand-boxed environments called 'containers' on your host
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- Its more than a "cheap VM"
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.. image:: https://iot.samteck.net/wp-content/uploads/2018/10/vm-vs-docker.jpg
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https://medium.com/@saschagrunert/demystifying-containers-part-i-kernel-space-2c53d6979504
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.. image:: https://cdn-images-1.medium.com/max/1600/1*bIQOZL_pZujjrfaaYlQ_gQ.png
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:class: dark-light
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Why docker?
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-----------
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- version-controlled binary dependency management
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- documented and repeatable dependency installation in a living (version-controlled) file
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2025-02-02 14:02:10 -05:00
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- "containerize once and run everywhere"
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2025-01-31 15:38:58 -05:00
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- No more "it works on my machine"
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- Industry-standard tool for CI/CD
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Why docker for development?
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^^^^^^^^^^^^^^^^^^^^^^^^^^^
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- consistent environment between developers and CI servers
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- Project environment isolation - useful when working multiple projects
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- Easy to experiment with and revert dependency changes - agile dependency management
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Docker and Linux
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-----------------
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- Docker is built atop core features of the Linux kernel (Namespaces) that are not available in Windows without WSL
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- Docker desktop requires a license for commercial use. Docker server/CLI does not
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docker image
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------------
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- Docker image is a snapshot of a linux rootfs
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- Images can be built manually or downloaded from a registry
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Command: ``docker image [--help]``
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docker registry
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---------------
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- Pre-built images published online you can download
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- Anyone can host a registry. Largest: https://hub.docker.com/search?q=
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Command: ``docker pull <image_name>``
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.. admonition:: Example
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Take a look at `example 1 <https://git.lenord.me/len0rd/docker_demo/src/branch/develop/01_registry_pull>`_
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docker container
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----------------
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- Container is a spawned docker image
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- Container *images* become *containers* at runtime
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- You can spawn many containers from a single image
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- Containers can run one or many processes, can provide user shells
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Managing existing containers: ``docker container [--help]``
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dockerfiles
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-----------
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- How you define custom images
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- Good documentation: https://docs.docker.com/engine/reference/builder/
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- Dockerfiles build off images. Each step in a dockerfile is a snapshot of changes to a linux rootfs
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Command: ``docker build --help``
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.. image:: ../assets/img/writeup/docker/dockerfile_as_layers.png
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:class: dark-light
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.. admonition:: Example
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Take a look at `example 2 <https://git.lenord.me/len0rd/docker_demo/src/branch/develop/02_simple_dockerfile>`_
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Running Containers
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------------------
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- when a container is run you are in full control of what parts have access to the outside world
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- ports forwarded from container to host
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- network configuration in general
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- mounting files/folders from the host within the container
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Running: ``docker run --help``
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docker cache
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------------
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- Every step in a dockerfile is cached. if a step in the middle of the file changes, the image is rebuilt from that point onward
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- https://docs.docker.com/build/cache/
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cache minimization
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^^^^^^^^^^^^^^^^^^
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- docker caches can take up a lot of space
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- Best practice is to combine logically linked commands into single steps to reduce the amount of cache a dockerfile build produces
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- clearing out old cache: ``docker builder prune``
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multi-stage builds
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------------------
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- newish (in the last couple years) feature, now standard is docker's BuildKit backend
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- allows definition of distinct stages in the dockerfile to allow parallel build and reduce unnecessary dependencies
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- https://docs.docker.com/build/buildkit/
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.. admonition:: Example
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Take a look at `example 4 <https://git.lenord.me/len0rd/docker_demo/src/branch/develop/04_multistage_docker_file>`_
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.. image:: https://git.lenord.me/len0rd/docker_demo/raw/branch/develop/04_multistage_docker_file/stage_graph.png
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:class: dark-light
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DevContainers: an additional layer on top of docker
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---------------------------------------------------
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- Feature first added by VSCode, eventually published as an open standard by Microsoft:
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- https://containers.dev/
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2025-02-02 14:02:10 -05:00
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- Now multiple IDEs (IntelliJ, Visual Studio, NeoVim) have support for the standard
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2025-01-31 15:38:58 -05:00
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.. image:: https://code.visualstudio.com/assets/docs/devcontainers/containers/architecture-containers.png
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:class: dark-light
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docker-compose: container orchestration
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---------------------------------------
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- ``docker run`` and ``docker build`` commands can get long and tedious for more complex containers
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- ``docker compose`` solves this. Sits on top of docker and supports building/running multiple containers via yaml
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.. admonition:: Example
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Take a look at `example 5 <https://git.lenord.me/len0rd/docker_demo/src/branch/develop/05_complex_run_with_compose>`_
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