HLD of the used technologies

What follow is just a very high level design of the technologies we are going to use on Arduino's side:

In a nutshell, I'm going to use the 32U4 to access our hardware (sensors, RTC and relays) providing a set of simple read and write API to a Python script running on the AR9331 processor. It stores/retrieves info in/from a MySQL (or sqlite) database. A web server is responsible to communicate with the client and provide/change info stored into the DB via PhP scripts.

This way:

1. the sketch will be very simple and 'light' and we shouldn't have any problem in uploading it into the small space provided by Yun;
2. all the logic to manage the sensors and actuators will be implemented with python scripts;
3. we will use the flexibility of a DB to store configurations, logs, sensors/actuators status and any other info we'd like to share with the rest fo the world;
4. a light web server will make easier the design and development (and test) of the interface we will provide to the final user.

Also there is another important reason why I'm choosing a web server based on PHP/MySQL technology: it's a common technology used by a lot of platform providing web hosting for free. When (in the future) I will create a website to manage my Arduino, I will just need to move my PHP scripts and MySQL structures/data to the new host. Maybe it will not be so easy, but I assume I can reuse 90% of the code.