Create your first Docker container

#docker #python

Part 1 of a multi-part essay on configuring Docker in production.

Prerequisites

  1. You have Docker installed (See instructions to install)
  2. (Optional) You know to to deploy a Flask application using command line

Docker works on basis of configurations. It’s a declarative way of telling Docker how to build images.

A typical workflow starts with a base image, works on top of it, saves it either for future use or gets reused as a base image of something else.

Creating Your First Image

Dockerfile

This file list down steps/configuration to build an image. In this example, we are trying to run a Flask application.

A bit of backstory on Flask applications

Typically, Flask applications have an entry point, server.py in this case. We can start the server by simply executing: python server.py, assuming that the current Python environment has all the dependencies installed. If not, we can install the dependencies from a requirements file.

# 1. Use this as the base image
FROM python:3.8-rc-slim

# 2. (Optional) Set the working directory to /app
WORKDIR /app

# 3. Copy the source code for deployment
COPY app /app

# 4. Install the dependencies
RUN pip install --trusted-host pypi.python.org -r requirements.txt

# 5. Make port 5000 available to the world outside this container
EXPOSE 5000

# 6. Run app.py when the container launches
CMD ["python", "server.py"]

Running the container

  1. To run the container, you first need to build it THis can be achieved like this:
sudo docker build --tag=gettingstarted .
  1. Once built, make sure it is present in your local registry
docker image ls

(More on this listing later, but you should see the container gettingstarted with latest tag here)

  1. Now is the time to run the container
docker run -p 5000:5000 gettingstarted

This runs the Docker container by the given name. The -p parameter is the port mapping from the host OS to the container.

That’s it! You have created your first Docker container!