Docker cheat sheet

1. 1Images, containers and the engineWhat an image is, what a container is, and the everyday commands for starting, listing and removing them.7 concepts

   1. 1ImageA read-only bundle of filesystem layers plus metadata (default command, environment, exposed ports, user).
   2. 2ContainerA running (or stopped) instance of an image: an isolated process with a thin writable layer on top of the image.
   3. 3Docker Engine, containerd and runcThe docker CLI talks to the dockerd daemon, which hands containers to containerd, which starts them with an OCI runtime such as runc.
   4. 4docker runCreates and starts a container from an image.
   5. 5Publishing ports-p host:container forwards a host port to a port inside the container.
   6. 6Container lifecycle commandsA container moves through created, running, paused, exited and removed.
   7. 7Tags and digestsA full reference is registry/namespace/name:tag@digest.

   7 in this chapterOpen this chapter
2. 2Writing a DockerfileThe instructions that turn source code into an image, and the details that decide how the container starts and stops.8 concepts

   1. 1FROM and base imagesFROM picks the starting image and begins a build stage.
   2. 2RUNExecutes a command at build time and saves the filesystem changes as a new layer.
   3. 3COPY vs ADDCOPY copies files from the build context into the image.
   4. 4WORKDIR, ENV and ARGWORKDIR sets the working directory (creating it).
   5. 5CMD vs ENTRYPOINTENTRYPOINT is the executable the container always runs; CMD gives default arguments, replaced by anything after the image name in docker run.
   6. 6Exec form and PID 1Exec form ["node", "server.js"] runs the process directly as PID 1.
   7. 7HEALTHCHECKAn instruction that runs a command inside the container on an interval.
   8. 8LABEL and OCI annotationsKey and value metadata stored in the image, such as org.opencontainers.image.source and org.opencontainers.image.revision.

   8 in this chapterOpen this chapter
3. Layers, caching and faster buildsHow the build cache works, how to keep it warm, and the BuildKit features that make builds quicker and images smaller.8 conceptsOpens with credits
4. Small and secure imagesChoosing a base, dropping root, keeping secrets out of layers and knowing what is inside the image you ship.7 conceptsOpens with credits
5. Storage and networkingWhere container data lives, how containers find each other, and what reaches them from outside.6 conceptsOpens with credits
6. Configuration, secrets and limitsPassing configuration in at run time, handling secrets, and keeping containers inside their resource budget.6 conceptsOpens with credits
7. Docker ComposeDescribing a multi-container app in one file and running it the same way on every machine.7 conceptsOpens with credits
8. Registries, tagging and multi-archGetting images from a build to the machines that run them, with names you can trust and platforms that match.6 conceptsOpens with credits
9. Debugging containersFinding out why a container will not start, keeps restarting, cannot connect or uses too much of the host.7 conceptsOpens with credits
10. 10Glossary, A to ZEvery concept in the sheet and the smaller terms it uses, in one list.85 terms

Images, Dockerfiles, caching, small secure builds, volumes, networks, Compose, registries and debugging containers.