Update presidio containers to use gunicorn

[RKapadia01]

Change Description

• Modified the main application entry points in presidio-analyzer/app.py, presidio-anonymizer/app.py, and presidio-image-redactor/app.py to use the app instance directly instead of creating a new Server instance when running the application.
• Added PORT and WORKERS environment variables to the Dockerfiles for all 3 services, to allow configuration of the server port and number of worker processes.
• Updated the command from Flaks to Gunicorn in the Dockerfiles

Issue reference

This PR fixes issue #1496

Checklist

• I have reviewed the contribution guidelines
• I have signed the CLA (if required)
• My code includes unit tests
• All unit tests and lint checks pass locally
• My PR contains documentation updates / additions if required

[omri374]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[SharonHart]

Looks great, thanks!

[omri374]

Looks great! Thanks :) I've added two minor points

[omri374]

Please add the gunicorn license into the NOTICE file.

[RKapadia01]

Updated the NOTICE file, thanks

[omri374]

I might be nit picking, but I'm curious on what is the difference between instantiating Server here compared to within the if name == main. For instance, if I import app.py, the Server instance would be instantiated. I'm not sure if importing app.py is a use case, but it would be a side effect of this change in case somebody does this anywhere. WDYT?

[RKapadia01]

Thats a great pickup. When running with Gunicorn, it doesn't execute the code in the__main__ block. It just imports the module and looks for the app object to serve the application, which is why I moved the server code out of the __main__ block.

However, I didn't remove the __main__ block entirely, so if anyone wants to run just the flask development server they still have to ability to do so.

To avoid your concern of instantiating the server on import of app.py, we can avoid it by doing something like this:

def create_app():
    server = Server()
    return server.app

if __name__ == "__main__":
    app = create_app()
    port = int(os.environ.get("PORT", DEFAULT_PORT))
    app.run(host="0.0.0.0", port=port)

We can then run Gunicorn in the Dockerfile like this:

CMD poetry run gunicorn -w $WORKERS -b 0.0.0.0:$PORT 'app:create_app()'

This should ensure that if anyone is just importing app.py it won't create the server instance. If you're happy with this, I'll commit the changes

[omri374]

Thanks! This is a better solution IMHO so let's go with it.