Useful commands for docker

Docker_Cheat_Sheet.md

Thanks to the tutorial Docker for Beginners from KodeKloud.

General

• Contains only live as long as their entry point is running
  • Running e.g. docker run ubuntu will exit as soon as ubuntu has finished starting
    • docker run ubuntu sleep 5 executes sleep 5 and then exits
• Find docker's files
  • Unix: /var/lib/docker
  • Windows
    • Run docker run -it --privileged --pid=host debian nsenter -t 1 -m -u -i sh
    • Navigate to /var/lib/docker

The docker commands

• Run a docker image (downloads it if not available)
  • docker run <user/image> (automatically tags it with :latest)
  • docker run <user/image:version>
  • Map a port
    • -p <host-port>:<container-path>
  • Run interactively, i.e. allowing the app to capture input from the console
    • -i and -it, the latter is helpful when linebreaks are different (ie running unix in a windows shell)
  • Run container in detached mode
    • -d
  • Map directory/volume on host to container
    • -v <host-path>:<container-path>
    • -v my_volume:/myvolume will create the folder /myvolume in the container and create the my_volume on the host
  • Set environment variable in container
    • -e <ENV_VAR>=<value>
    • You can find out which environment variables are set by using docker inspect
  • Change the entrypoint
    • --entrypoint sh
  • Pass parameters to the entry point / configure the entry point
    • For the ubuntu image the entry point bash but when you're not running interactively, it'll immediately exit
    • To pass in parameters to it (which, because it's bash, will be run), append them: docker run ubuntu sleep 5
      • To make this permanent, create a new image with the Dockerfile containing:

        From ubuntu
        CMD ["sleep", "5"]
        

    • Pass parameters to the entrypoint's program

      From ubuntu
      ENTRYPOINT ["sleep"]
      CMD ["5"]
      

      And docker run ubuntusleeper 7 will result in sleep being called with the parameter 7 while docker run ubuntusleep will result in the default parameter 5 for sleep
    • --link <containerid/name>:<alias>
      • Creates an entry in the hosts file for the host name <alias> and linking to the ip of <containerid/name>. This is deprecated in favor of user-defined networks!
      • If containerid/name and alias are the same, one may use --link <alias>
    • Performance
      • --cpus=0.5 limits the container's CPU usage to 50% of the host's CPU
      • --memory=100m limits the memory usable by the container to 100MB
  • Networks
    • --network=<network>
    • Bridge
      • It's the default
      • Contains get their own IP and thus different containers can use the same port, since it's like they're on different machiens
      • IPs are usually 172.0.0.2 and onwards
    • None
      • No network available
    • Host
      • Runs in host network
      • IP same as host
      • Ports usable only once
    • Networks can be created with docker network create ...
• Attach to the terminal of a running container
  • docker attach <containerid>
  • Disconnect with ctrl+c
• List containers
  • docker ps
  • In the PORTS column you will see the published ports.
    • e.g. 0.0.0.0:3456->3456/tcp, 0.0.0.0:38080->80/tcp where 3456 and 80 are the ports on the container and 3456 and 38080 are on the host, forwarding to the container.
  • List all
    • docker ps a
• Stop/Remove a continer
  • docker stop <containerid> [<containerid2> ..]
  • docker rm <containerid> [<containerid2> ..]
• Images
  • List
    • docker image ls
  • Remove
    • docker image rm <imageid>
• Details of a container
  • docker inspect <containerid> will yield all information in JSON
  • To get the IP address
    • docker inspect -f "{{ .NetworkSettings.IPAddress }}" <containerid>
• Logs
  • docker logs <containerid>
• Building an image
  • docker build -t <name>[:<tag>] <foldername>
    • In that foldery there must be a file called Dockerfile (upper case D!)
• See layers in image and their sizes
  • docker history <imageid>
    • Example: ubuntu 120MB, python 300MB, pip packages 5MB, source code 500B)
  • The layers are cached, to speed up building of images
• Network
  • ls List all
  • docker network create --driver bridge subnet 182.18.0.0/16 custom-isolated-network creates a new one with the given IP range and name
  • To connect to others hosts on the same network, one can use
    • their IP, but that's not optimal as it can change etc
    • their container name, which is resolved via DNS (the server is at 127.0.0.11)

Docker Compose

Name the file docker-compose.yml and run docker-compose up

version: "2" # must be string
services:
  web:
    image: "mmumshad/simple-webapp"
  database:
    image: "mongo"
  messaging:
    image: "redis:alpine"
  orchestration:
    image: "ansible/galaxy"
  myapp:
    build: ./myapp # instead of pulling an image from docker, build this folder
    ports:
      - 5000:80 # map host:5000 to container:80
    links:
      - database # link to mongodb, no longer required from 2 onwards
    depends_on:
      - messaging # messaging must start before this one
    

From version 2 onwards:

• all containers are within services:
• a dedicated network is created so links are no longer required since the container names are resolvable via DNS

From version 3 onwards:

• Docker swarm is supported

Docker image registries

When specifying an image in docker run <image> or a docker-compose.yml file, the format is: registries/username/imagename:tag

• registries if omitted will default to docker.io but there's also gcr.io for google's kubernetes related images and many other.
• username is the name of the registered user on docker
• imagename is optional as well, some users publish only a single image under their name alone
• tag is optional and will default to :latest

Private repositories/images

Some registries allow to mark images as private, requiring login credentials

• docker login <private-registry-url> will query you for credentials
• docker run <private-registry-url>/<image> then should work if the user used above has access to <image>

Run your own registry

There is a docker image called registry that serves a docker registry.

• docker run -d -p 5000:5000 --name registry registry to start it
• To push an image to the registry
  • docker image tag my-image localhost:5000/my-image to tag it
  • docker push localhost:5000/my-image and push it
• `docker pull

Running Windows Containers

When on Windows, Docker utilizes Microsoft's Hyper-V to run Linux Containers. To run Windows containers, go to the task bar, right click on the Docker icon and select Switch to Windows containers