They are nothing more than a text file called Dockerfile with the instructions which are required to build a container. Then, each instruction is called a Layer. Following an exemplification.
FROM ubuntu:18.04 COPY . /app RUN make /app CMD python /app/app.py
See what it is doing:
- FROM the ubuntu:18.04 means from where it will start. The ubuntu:18.04 is a Docker image of the Ubuntu SO and 18.04 is its tag/version of it.
- Then, COPY and RUN are instructions to copy all from the current dir to /app and execute the command line
$ make /app.
- Note that the last instruction is the CMD which means that it will be the command executed when the container be initialized to run the application.
Perform the following exercise to learn how to create it.
Also, please feel free to check the tag docker of this website to see all related blog posts.