04. Dockerfile

Dockerfile Basic

Basic Rules

• Every reserved words command need to use upper case and follow at least one argument
• The commands are executed from top to bottom as order.
• # means comment
• Every command will create a image layer to commit to final image.

How the docker parse Dockerfile

1. docker to run a container from a basic image
2. execute a command to modify container
3. execute a command similar with docker commit to commit a new image layer.
4. docker to run a container based on the commited image.
5. execute the next command untill finish all the commands.

Reserved Words

• FROM: specify the basic image as template, normally it's the first command
• MAINTAINER: the maintainer's info, name and email
• RUN: execute commands during building docker image
  SHELL: RUN yum install vim
  EXEC: RUN ["execute file", "param1", "param2"]
• EXPOSE: Expose port to outside
• WORKDIR: Specify the working directory after creating a container.
• USER: Specify the user need to execute, default is root
• ENV: Setup the environment variables during building.
  ENV MY_PATH /root
• VOLUME: Container volume
• ADD: copy host file to docker, the url can be processed automatically, and tar file will be decompressed automatically also.
• COPY: copy host file to docker
• CMD: Specify the commands that need to be executed after run a container.
  ::: notes
  The CMD can appear multiple times, but only the last one is valid. And it will be replaced by docker run command
  :::
• ENTRYPOINT:
  • To specify a command when a container startup.
  • Similar with CMD, but it can not be overwritten by docker run commands, and the commands will be the parameters to the script and specified by ENTRYPOINT.

Reference

1. Tutoriaspoint
2. Docker Dockerfile on runoob
3. Dockerfile reference (official)