Writing good Dockerfiles

Tips on writing good Dockerfiles

1. Avoid installing unnecessary packages, and re-installing packages

Use a requirements.txt file to install all required packages at once instead of re-installing them each time.

Reason: To reduce the size and build time of the docker image.

1. Chain RUN commands

Reason: Each RUN command creates a cacheable unit, and creates a new image layer. This can be avoided by chaining RUN commands.

e.g.

RUN sudo apt update
RUN sudo apt install firefox

``` Dockerfile   
RUN sudo apt update \   
    && sudo apt install firefox   
```

1. Use a .dockerignore file

Reason: Removes unnecessary files from the docker image, reducing its size and build time.

1. Use the best order of statements

Include the most frequently changing statements at the bottom of the Dockerfile.

e.g. RUN commands at the top and COPY commands to the bottom. CMD and ENTRYPOINT should be defined at the end of the Dockerfile.

Reason: When you change a statement in your Dockerfile, its cache gets invalidated, and all the subsequent statements' cache will also break.

1. Avoid installing unncessary package dependencies

e.g. Use the --no-install-recommends option with APT while building the image.