Docker Cookbok

Quick concepts

Linux containers are a way to create isolated environments that can run code while sharing a single operating system.

  • A container is an isolated environment, comprised of binaries and libraries, created on top of an existing OS.
  • An image is like a blueprint for a container.
  • A Dockerfile is like a recipe for an image
  • Docker acts as a mediator between the OS and the containers
  • A single OS can run multiple containers

Quick commands

  • docker container ls lists all running containers
  • docker container run <image>:<version> runs a container
  • docker container exec <container name or ID> <command> runs commands against a container
  • docker container cp <source file> <cont name or ID>:<destination path/file> copies assets from local machine to a container (assets will not be persisted)
  • docker run -v <local files path>:<container files path> <img name>:<img ver> creates a data volume (-v): maps a file or folder on the local machine to a destination on the container. This way we can persist files on an image
  • docker container exec -it <container name or ID> <chosen shell, i.e. /bin/bash> attaches a shell to a container
  • docker image build --tag <img name>:<img ver> <Dockerfile path> builds an image from a Dockerfile
  • Flags
    • The -d or --detach flag runs a container in the background
    • The -t or --tag passes to the build command the name and version of our image

Run a docker container based on an image

# docker container run <image>:<version>

docker container run httpd:2.4

Map ports on a container

# docker container -p <host port>:<container port> run <image>:<version>
# where -p = 'publish ports'

docker container run -p 9999:80 httpd:2.4

If we access http://localhost:9999/index.html we'll see the server's default test page; we mapped port 9999 on our host to port 80 on the container.

Update an environment variable

docker container exec -it <container name or ID> /bin/bash
PATH=$PATH:<value>
export PATH

Create a Dockerfile

Warning: a Dockerfile must use a capital "D".

FROM httpd:2.4 # the image we're using as a starting point (our image will be based on this image)
EXPOSE 80 # the container port we're exposing
RUN apt-get update && apt-get install -y fortunes # commands we want to execute when building the image
COPY <target path> <destination path> # the specified local files will be copied to the container (subsequent modifications will not be persisted)
LABEL maintainer="moby-dock@example.com" # creator info