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basic docker commands

Aug 28, 20243 min read

docker provides the ability to package and run an application in a loosely isolated environment called container.

docker cli

the docker engine consists of three parts:

  • docker cli
  • docker rest api
  • docker daemon

When you run a command, behind the scenes the client sends a request through the REST API to the docker daemon which takes care of images, containers and other resources.

docker management commands like compose, image, system, etc. follow this semantics.

docker COMMAND SUBCOMMAND [options] [arguments]

container

  • lightweight
  • independent - they contain everything required to run an application
  • leverages kernel namespaces and cgroups
  • can interact with the host machine via. TCP / UDP
docker run --name container-name -dp 8080:3000 image-name:tag

above command runs a container, downloads if it does not exist locally.

  • -d → detached mode, runs in background
  • -p HOST:CONTAINER → port map, maps port 3000 in the container to 8080 in the host machine
  • you could also run docker container run, it follows the docker COMMAND SUBCOMMAND semantics

docker container sub-commands

e.g. docker container SUBCOMMANDS

  • ls → lists all running containers
    • -a: all containers and -s: for size
    • same as docker ps or docker container ps
  • start / stop → start / stop container (-d: detached mode)
  • rm NAME|ID1 NAME|ID2 ... → delete a container (you need to stop it first)
  • prune → delete all stopped containers
  • exec NAME|ID COMMAND → execute a command inside a container
    • e.g., docker exec 918ffd ps -a

image vs container

a container is the food while an image is the recipe.

  • you cannot change an existing image.
  • to create new images, you start with a base image and add layers to it.
  • dockerfile contains those layered instructions to build an image.

docker image sub-commands

e.g. docker iamge SUBCOMMAND

  • build → builds an image from a dockerfile
  • pull IMAGE:TAG → downloads an image from registry
  • push IMAGE:TAG → push an image to registry
  • rm NAME|ID1 NAME|ID2 ... → delete an image
    • you should always delete all containers related to the image first, then delete the image.
  • prune → removes “dangling images” - these are images that have no name.
    • -a → removes all images not associated with a container.

docker system prune → removes everything:

  • all stopped containers
  • all networks not used by at least one container
  • all dangling images
  • unused build cache

copy, history, commit

you can copy files from host machine to your container and vice versa using docker cp or docker container cp. If you are mentioning the container path, it should be of this format: CONTAINER-ID|NAME:CONTAINER-FILE-PATH.

docker cp SOURCE DEST
---
e.g., docker cp /hello.txt c99d19efdab3:/usr/src/app/hello.txt

since we changed the container, you can use docker diff ID|NAME command to check all the changes made in the container. A=added; D=deleted; C=changed.

you can build an image from an container using docker commit. its generally better to use a dockerfile instead as defining the changes to the Dockerfile is much more sustainable method of managing changes.

docker commit CONTAINER-ID|NAME IMAGE-NAME

contents

creating container from scratch → https://youtu.be/8fi7uSYlOdc namespaces, cgroups, union filesystems

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