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Docker

A platform for building, shipping, and running application in multiple environments.

Images and Containers

Image is a read-only template of the app used to build a container. Container is actually running the application (an instance of an image).

Containers vs VMs

Virtual Machines are complete OSs, they are big and slow to start/stop. Containers are smaller and faster, they are not copies of a whole OS.

Docker Toolbox

  • Docker Client - manage containers

    • $ docker images - list installed (available) images
    • $ docker rmi <image-id> - remove image
    • $ docker rm <container-id> - remove container, -v option removes also the associated volume (only if the host dir was automatically created )
    • $ docker ps - list containers, -a option shows all (not only running containers)
    • $ docker run <image-name> - set up a container
    • $ docker exec -it <container-id> <command> to execute a command in the container, e.g. docker exec -it c4cb6fa51bde /bin/bash

  • Docker Machine - manage VMs

    by default there is one machine, called default

    $ docker-machine env <machine-name> hooks up $ docker command to the machine (sets up env variables). This has to be done for any new session.

  • Docker Composer - container management

  • Docker Kitematic - GUI

  • VirtualBox - to run VMs

  • Docker Hub - Cloud-based repository of images.

$ docker run

$ docker run <image-name> - set up a container, if it's not found locally, docker will try to docker pull the image from Docker Hub.

  • -d start in background
  • -v sets up a volume
  • -w sets the working directory (from where should the starting command be executed)
  • -p sets the port. can map - -p 8080:3000 (link machine's 8080 port to app's 3000 port)
  • anything after this command is the command to run in the container, e.g.: $ docker run -p 8080:3000 -v $(pwd):/var/www -w "/var/www" my-node-container npm start

nginx example: $ docker run -p 80:80 kitematic/hello-world-nginx

Layered File System and Volumes

  • a volume is a special type of directory in a container. Typically a data volume
  • volumes can be shared and reused among containers
  • a volume is really an alias to a folder in the host

$ docker run -v /var/www <image-name> will create a volume. To reveal that volume in host system, $ docker inspect <container-id> - 'Mounts' section . We can specify that host location with $ docker run -v /local/path:/var/www <image-name> (or with pwd - -v $(pwd)/src:/var/www)

Dockerfile

contains Docker image build instructions

  • FROM - defines what the image is based on (e.g. node)
  • RUN - the commands to run

example:

FROM node
COPY . /var/www
ENV NODE_ENV=production
ENV PORT=3000
WORKDIR /var/www
RUN npm install
EXPOSE $PORT
ENTRYPOINT ["node", "server.js"]

to build it:

docker build -t <tag-name>/node .

Container linking and networks

  • docker run --name <custom-name>, docker run --link <custom-name>
  • docker network --create <network-name> --driver <driver-name>, docker run -net=<network-name>

Docker Compose

managing application lifecycle - multiple services

docker-compose.yml - defines relationships between services (containers)

version: '2'
services:
  node:
    build:
      context: .
      dockerfile: node.dockerfile
    ports:
      - "3000:3000"
    networks:
      - nodeapp-network
  mongodb:
    image: mongo
    networks:
      - nodeapp-network
networks:
  nodeapp-network:
    driver: bridge
  • $ docker-compose build
  • $ docker-compose up - start it all (-d to run in background)
  • $ docker-compose down - stop and remove containers

Docker Cloud

Managing cloud deployments. Set up on cloud.docker.com.

A Stack is like Docker Compose, but in the cloud.

sources: