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Dockerfile

Dockerfile specifies all the configurations to build an image.

Instruction

  • FROM: base image
  • LABEL: replace the previous MAINTAINER, metadata for the image
  • ENV: define environment variables to be used by RUN, ENTRYPOINT, CMD
    • ENV MY_VERSION 1.3
    • RUN apt-get install -y mypackage=$MY_VERSION
  • RUN: effectuate actions as:
    • install packages
    • modify configuration
    • create links and directories
    • create users and groups
  • COPY/ADD: copy files from the host to the container
    • COPY index.html /var/www/html/index.html
    • COPY ["index.html", "/var/www/html/index.html"]
    • ADD: can unzip tar, zip, taz files
  • VOLUME: create default mount points
    • VOLUME ["/etc/mysql/mysql.conf.d", "/var/lib/mysql", "/var/log/mysql"]
  • WORKDIR: switch path inside the container
  • EXPOSE: export a TCP port on the container
  • CMD: command to be run when launch the container
    • if there are multiple CMD, only the last will be run
    • docker container run NEW_CMD: will be replaced by the NEW_CMD
  • ENTRYPOINT: command always to be run when launch the container, usually to launch a daemon
    • always run even if add another NEW_CMD
    • docker container run NEW_CMD: NEW_CMD will be added as parameters to ENTRYPOINT
  • USER: execute the commands with which user
  • ONBUILD:
  • HEALTHCHECK:
  • SHELL: use which shell to execute commands

Build Image

  • docker image build create a new image using the instructions in the Dockerfile
    • docker image build -t apache2-demo:v1 .: -t stands for tag/name
    • docker image build -t apache2-demo:v1 -f DockerfileXXX .: -f use a Dockerfile with an arbitrary name
  • docker image history apache2-demo: show image build history

ENV

Shell Env

  • docker build -t img1 -f Dockerfile-env .: create the image
  • docker run --name ct1 --rm img1: see the default msg in default file /tmp/xxx.log
  • docker run --name ct2 --rm -e MSG=111 img1: see the new msg

Python Argparse Env

  • docker build -t img1 -f Dockerfile-env-python .: create the image
  • docker run --name ct1 --rm img1: see the default msg
  • docker run --name ct2 --rm -e MSG1=aaa -e MSG2=bbb img1: see the new msgs

Using the same image to launch different Python scripts

  • docker build -t img1 -f Dockerfile-env-python2 .: create the image
  • docker run --name ct2 --rm -v $(pwd):/workspace img1: launch the default script
  • docker run --name ct2 --rm -v $(pwd):/workspace -e APP=/workspace/app2.py img1: launch the new script

Example

Apache2 Web Server

  • write a Dockerfile to create an image with packages php, apache (apache2, libapache2-mod-php)
  • add a index.php file with: <?php phpinfo() ?>

See the Dockerfile as the answer

  • docker image build -t apache2-demo .
  • docker container run -d -p 8885:80 apache2-demo
  • test:
    • http://localhost:8885/index.php: NAT access through browser
    • http://172.17.0.2:80/index.php: direct access through browser