I have more progress in ESP8266 as MQTT broker.
What I have for now on this ESP8266 module:
- MQTT broker functionality
- Bridging data to/from and another MQTT broker ( usually a cloud MQTT instance)
- websockets connectivity ( I can now connect with my Homy application directly to the ESP8266 acting as an MQTT broker)
- OTA (Over The Air) updates. Every time I have a new software update the ESP8266 is updating itself so, I can say that I have continuous integration (CI) and continuous deployment(CD). Also all the modules are activated over the air.
With all those function in place I still have 34kb of heap available for other features and yes is running on an ESP with a minimum 1Mb of memory. ESP8285 is a good candidate for running the broker.
Is working also on and old ESP-01 with 512kb but without OTA functionality.