In this tutorial, we are going to do some initial setup necessary for WebSockets. We would need FastAPI for sure and internally we are going to use Redis for its pub-sub capabilities. FastAPI when combined with Docker, a powerful containerization platform, it becomes even easier to deploy, manage, and scale FastAPI applications.
Docker is a containerization platform that simplifies the packaging and distribution of applications, making them portable and consistent across different environments. Containers provide a lightweight and isolated runtime environment for your applications, reducing conflicts and compatibility issues.

Before we dive into Dockerizing our FastAPI application, let's first set up a basic FastAPI project. Make sure you have Python installed on your system. create a file named codeshare/main.py

from fastapi import FastAPI 

app = FastAPI()

We also have some requirements for FastAPI, WebSockets and Redis too. Let's create a requirements.txt for it.

fastapi==0.100.0
uvicorn==0.23.1 

Now, coming to the docker part, We are going to create a Dockerfile that will have steps on starting the fastapi server. Since fastapi will not be the only service, we might have a Redis service, maybe a Postgres service. So, we also going to have a docker-compose.yml file to manage the different services together. Create a file named Dockerfile (without any file extension) in the project directory and add the following content:

FROM python:3.9

# Set the working directory in the container
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY . .
EXPOSE 8000
CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]

Docker Compose, on the other hand, is a tool for defining and running multi-container Docker applications. It simplifies the process of managing multiple containers and their interactions. Now, let's give wings to our FastAPI app with Docker Compose. Create a new file named docker-compose.yml in the project directory and let the creativity flow. This is our docker-compose.yml file.

version: '3.8'

services:
  web:
    build:
      context: ./
      dockerfile: Dockerfile
    ports:
      - "8000:8000"
    environment:
      - ENV_VAR_NAME=VALUE
    depends_on:
      - redis

  redis:
    image: redis:latest
    ports:
      - "6379:6379"

Now, we can start the docker container by using : docker compose up --build

Note that the --build flag will be needed once we make a change in the code and we need the changes to be picked up by docker. Normally, we do not want to install the requirements everytime. So, we simply use:

docker compose up