Dear friend,

You have learnt the theory of how Docker and container images work.

It’s time to apply that knowledge to write a Dockerfile.

After that, you can tell all your friends you’re a certified Docker pro.

Here are the 5 steps.

Docker images consist of layers.

First, you need to pick a base layer (image).

You can build it yourself.

But it’s much more convenient to pull a prebuilt base image with everything we need.

Here’s how to do it.

Go to Dockerhub, search for Python.

Dockerhub is like PyPi but for container images.

Pick one with the Python version and operating system you need.

Then, in the Dockerfile, use the FROM command to use that as a base image.

You just added the tools to the container.

But it doesn’t have any meaningful file or code.

So, we need to copy our program into it.

To do that, first you need to select a work directory.

Let’s set it to:

Before running your code, you need to have the dependency ready.

So, copy in your requirements.txt

Then install the dependency with the RUN command.

This runs the pip install command in the container’s shell.

This is pretty straightforward to do:

Now you have all the files ready to run your code.

You need to set a command to start your app.

Your first intuition may be using the RUN command again:

But that’s not what we want to do. The run commands run during the image building process.

We want to run the command only when we are actually starting a container.

To do that, use the CMD command:

And this is the final result:

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