A Docker image contains the code used to create a Docker container, such as creating a Nginx web server, or a mySQL server, or a home grown app, and the list goes on. In this way, an image is like a template used to create a container. An image is kind of like a virtual machine, but much more light weight, using significantly less storage a memory (containers are usually megabytes in size).

There are two Docker repo's that are commonly used for Flask:

• tiangolo/uwsgi-nginx-flask (this article)
• tiangolo/meinheld-gunicorn-flask

According to https://hub.docker.com/r/tiangolo/uwsgi-nginx-flask:

"tiangolo/meinheld-gunicorn-flask will give you about 400% (4x) the performance of this tiangolo/uwsgi-nginx-flask"

So unless there is some reason you must use tiangolo/uwsgi-nginx-flask, I would go with tiangolo/meinheld-gunicorn-flask.

The docker pull command can be used to pull down the latest nginx image.

sudo docker pull tiangolo/uwsgi-nginx-flask:latest

Or, create a file named Dockerfile so that the Dockerfile contains the following.

FROM tiangolo/uwsgi-nginx-flask:latest

Then use the docker build command to create the image, running this command in the same directory as the Dockerfile.

docker build --tag uwsgi-nginx-flask-python3.11 .

The docker images command can be used to display the image.

~]$ sudo docker images
REPOSITORY                     TAG          IMAGE ID       CREATED         SIZE
tiangolo/uwsgi-nginx-flask     latest       60b476e79885   5 days ago      968MB

Create a file somewhere on your Docker system such as /usr/local/docker/flask/main.py that contains the following.

from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World"

if __name__ == "__main__":
    app.run(host='0.0.0.0', debug=True, port=80)

The following command can then be used to create and start the container. Let's break down this command.

• The docker run command is used to create and start the container.
• The --detach flag is used to run the container in the background.
• The --publish option is used both the Docker server and container to listen on HTTP port 80, which adds a rule to iptables to allow connections between the Docker system and container on port 80.
• The --volume option is used to mount the main.py file on your Docker system to /app/main.py in the container.
• The --name option is used to give the container a specific name.
• The --restart unless-stopped option is used so that the container is started if the Docker server is restarted
• The uWSGI Nginx Flask image is used.

sudo docker run --detach --restart unless-stopped --publish 0.0.0.0:80:80 --volume /usr/local/docker/main.py:/app/main.py --name flask tiangolo/uwsgi-nginx-flask:latest

The docker container ls command can be used to ensure the container is running.

~]$ sudo docker container ls
CONTAINER ID   IMAGE                COMMAND                  CREATED              STATUS                 PORTS                             NAMES
be0cc8e9aa4d   uwsgi-nginx-flask    "/entrypoint.sh /sta…"   About a minute ago   Up About a minute      443/tcp, 0.0.0.0:80->80/tcp    flask

The docker logs command should return something like this.

~]# sudo docker logs uwsgi-nginx-flask
2022-12-17 03:47:14,238 INFO success: quit_on_failure entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)

If running Docker on a Linux system, ensure connections are allowed in firewalld or iptables on ports 80 and 443.

firewall-cmd --add-service=http --permanent
firewall-cmd --add-service=https --permanent
firewall-cmd --reload

If running Docker on an Amazon Web Services (AWS) EC2 Instance, ensure the Security Group Inbound Rules allow connections on ports 80 and 443.

You should then be able to access main.py should be returned to return Hello World at http://<hostname or IP address of your Docker system>.

And now the docker logs command should return something like this, the nginx log showing the GET request to the / endpoint.

~]# sudo docker logs uwsgi-nginx-flask

192.168.0.193 - - [23/Apr/2024:00:18:37 +0000] "GET / HTTP/1.1" 200 164 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36 Edg/124.0.0.0" "-"
[pid: 13|app: 0|req: 3/5] 192.168.0.193 () {42 vars in 828 bytes} [Tue Apr 23 00:18:36 2024] GET / => generated 164 bytes in 254 msecs (HTTP/1.1 200) 2 headers in 80 bytes (1 switches on core 0)