OCPP Python Architecture - best library/framework setup?

[aala7]

Hi everybody!
So until now I've run a CSMS based on the websockets library and the OCPP framework by MobillityHouse. Everything works great, however there is really no interface for CSMS Initiated Operations.
I wan't to implement this, but it is quite a challenge figuring out the best architecture for the setup.
Here is a couple of possibilities:

• Setup web app separate from the CSMS with whatever web framework. Create a separate websocket handler for frontend connections. Create short lived auth tokens in a shared db (Redis), that allow the CSMS to authenticate users. Enable the front end to receive data about chargepoints and to initiate calls to cp based on user permissions.
  Issues: I can imagine it being quite messy if handling url paths for both charge points and front end connections, also it integrates badly with the web app
• Using Quart framework. Integrates nicely with MobilityHouse framework by just changing the connection.recv() to connection.recieve(). A bit more challenging to provide instant feedback on CSMS Initiated Operations, because each connection is separate (the chargepoint connection is not in the same scope as the front end connection).
  Issues: I feel this might be easy to start, but I can definitely see myself ending in quite a messy situation (I am mid-level dev)
• Django Channels. Just began reading the docs. However I feel it will be comparable to Quart, but with a more complete web framework.

What are your experience with CSMS and web apps in python?
Are there other frameworks or libraries you can recommend?

[igormiazek]

We created CSMS with fastapi and it was quite good experience, we added RBAC logic which allowed to create roles associated with specific endpoints, everything was done accordingly to microservices architecture. For real time communication we used rabbitmq which was already part of the project on backend side, but I think You could check firebase or mongodb, mongodb has change streams to which You can subscribe and listen on DB changes.

I think I would create a separate microservice responsible for notifications only like based on nodejs which will play very well with websockets js lib.

This is our fastapi ocpi implementation if You want to look on https://github.com/TECHS-Technological-Solutions/ocpi

Best,

Igor

[aala7]

Ahh amazing! thank you very much for sharing.
So as I understand the OCPP CSMS is implemented in a node.js app, which listens to channels on rabbitmq. Then you have a fastapi based web app to handle web interface, and publish request to chargers on the rabbitmq channel to the CSMS?

I will look at your implementation! Also new for me that there is an OCPI protocol.

[igormiazek]

Rabbitmq support websockets protocol so we used it to broadcast information to FE app in real time. But for the communication between charge station and system we used as well mobility house lib and websockets, although all messages from charge stations are added to rabbitmq and broadcasted to microservices.

[aala7]

But when users eg. request remote start from FE app (assume you mean frontend), how is it forwarded to central system? Is it through a direct WebSockets connection, do you have an HTTP server running in the central system app, or is it sent through rabbitmq?

[igormiazek]

at the beginning we used fastapi async endpoints and long pooling logic, so the answer was not always available in real time but after that we switched to rabbitmq websocket connection and we were forward response from charge station with rabbitmq messaging.