1-efficient-docker-files

Creating your first Images with Docker

About this exercise set

To help the users of this exercise to learn how to use docker and where to get help when they are stuck in the real world, I have tried to create exercises that forces the user to look in documentation and experiment.

This means, that the exercise set is not a simple copy & paste exercise

This folder contains a very small docker container, capable of adding two numbers.

Looking at the order of the layers when building

Start by using the addition.py from last exercise, with the following dockerfile:

Bad dockerfile

FROM python:2.7-alpine
COPY addition.py /
RUN pip install web.py
ENTRYPOINT ["python", "addition.py"]

Build the app

Build the image using the following command.

$ time docker build -t add-a-tron-server .

This builds the images for us and when the is done the time command prints the total time spend on the build. If you do this a couple of times you should see that all the docker cache magic makes the build very fast.

Exercise: Try to edit the addition.py file. How long does the build take now?

Good dockerfile

Now lets try to sort the lines after what changes most rarely.

FROM python:2.7-alpine
ENTRYPOINT ["python", "addition.py"]
RUN pip install web.py
COPY addition.py /

Build the app

Exercise: After a couple of builds you should see that all the docker cache magic makes the build very fast. BUT Try to edit the addition.py file (to a version that you have not had before; docker also caches older versions of the files). How long does the build take now?