How to Run/maintain "one" CI3 App hosted on multiple subdomains/ servers.

Hi,

A year ago i've started developing an application in CI3. The general idea behind this was that every client would have a seperate (sub)domain with their version of the application/db (stand-alone) so each client worked in his own "bubble" with no connection to the others. Now a year later the amount of clients is growing and I currently have 10 subdomains with running the app.

This is becoming a bit complicated to maintain when I want to update the app(s). I've been looking at deployment tools and services and i'm a bit lost here   . My goal is to simultaneously update all my subdomains when i push to my git repo. and have the least amount of downtime. (Some of the clients have the application running on their own servers as well). Is there anyone with some experience with a similar problem / case?

Alternatively i was think about putting the base source-code of the application outside the www/ folder and have all the subdomains use this code. So basically have a index.php in a subdomain where i include some constant variables which contain the config variables and the database connection information so it all uses one codebase (like codeigniter does with system folder). But i'm not sure that this is a good approach because well first of all passing constants in the index file (security risk?), one codebase -> one error and all clients are affected instead of one! And performance issues.

As you might notice i have no idea what the best approach here will be. Advice on this matter would be very appreciated! Are there people who faced the same issue or who know how to handle these kinds of things. Any form of help is welcome, advice, tutorials, ...

Thanks in advance!

Best regards,
Bart