Question on 3 tiers architecture with Swift backend

Hi Swift Users,

I want to build and apps like following architecture

Tier 1
Mobile and Browser

Tier 2
Swift Linux Apps (getting alot of JSON from Tier 3 and pass to Tier 1? )

Tier 3
MySQL database

My question is:

I have alot of SQL queries API to the database that I would like to be
place in Tier 2.
Currently what is the best approach to achieve this?

Thanks

Regards,
Xing