I could reach out Endel and post his anwser here:

"
We've recently included a RedisDriver as well, so MongoDB is not mandatory if you use RedisDriver.
https://www.npmjs.com/package/@colyseus/redis-driver

I just noticed this is not documented yet, gonna document it for the next version!

Cheers"

I have two questions to get a better understanding about scaling colyseus

1. The documentation is stating that you need both, redis and mongo. I would like to understand why. Why do you need redis and mongo to get scaling? Wouldn't redis be enough?

2. When the proxy is used, is each client routed to the process where the room was created/reserved or do they simply connect to any process/server and then communicate via redis?

Thx for any hints :)