feat(docker): add production docker lecture

Keep information on how to run locally using Flask dev server and volumes

Author: jslvtr

docs/docs/11_deploy_to_render/03_docker_with_gunicorn/README.md

@@ -0,0 +1,70 @@
+# Run our Flask app with gunicorn in Docker
+
+Throughout the course, we've been working with a Docker image like this one:
+
+```dockerfile
+FROM python:3.10
+EXPOSE 5000
+WORKDIR /app
+COPY requirements.txt .
+RUN pip install -r requirements.txt
+COPY . .
+CMD ["flask", "run", "--host", "0.0.0.0"]
+```
+
+This is all well and good for local development, but when we deploy our application we want to run it with the best performance possible.
+
+This is why we don't want to run the Flask development server and the Flask debugger. Instead, we'll use gunicorn to run our app.
+
+## Run our Flask app with gunicorn
+
+First let's add `gunicorn` to our `requirements.txt` file:
+
+```text title="requirements.txt"
+flask
+flask-smorest
+python-dotenv
+sqlalchemy
+flask-sqlalchemy
+flask-jwt-extended
+passlib
+flask-migrate
+# highlight-start
+gunicorn
+# highlight-end
+```
+
+Then, let's change our `Dockerfile` to use `gunicorn`:
+
+```dockerfile
+FROM python:3.10
+WORKDIR /app
+COPY ./requirements.txt requirements.txt
+# highlight-start
+RUN pip install --no-cache-dir --upgrade -r requirements.txt
+# highlight-end
+COPY . .
+# highlight-start
+CMD ["gunicorn", "--bind", "0.0.0.0:80", "app:create_app()"]
+# highlight-end
+```
+
+The `CMD` line change is the important one, as it runs `gunicorn` on port `80`, and we pass in the app factory function.
+
+:::tip
+Note I've also changed the `pip install` line. Adding `--no-cache-dir` and `--upgrade` just makes sure we can't accidentally install from a cache directory (which shouldn't exist anyway!), and that we'll upgrade to the latest possible versions allowed by our `requirements.txt` file.
+:::
+
+## Run the Docker container locally with the Flask development server and debugger
+
+If you use this `Dockerfile`, it doesn't mean you can't run it locally using the Flask development server. You don't have to lose the automatic restarting capabilities, or the Flask debugger.
+
+To run the Docker container locally, you'll have to do this from now on:
+
+```zsh
+docker run -dp 5000:5000 -w /app -v "$(pwd):/app" teclado-site-flask sh -c "flask run"
+```
+
+This is similar to how we've ran the Docker container with our local code as a volume (that's what `-w /app -v "$(pwd):/app"` does), but at the end of the command we're telling the container to run `flask run` instead of the `CMD` line of the `Dockerfile`. That's what `sh -c "flask run"` does!
+
+Now you're ready to commit and push this to your repository and re-deploy to Render.com!