Hello , Our first version of www.voilacabs.com was programed with Code Ignitor PHP API's, and at times during peak hours when there were huge request's made the response time use to vary from 500 MS to 1 Minute, also at time's we might have to end up restarting PHP-FPM which use to bring things to normal.

Also PHP lacks features like promises queue, Asyc task, etc. which is supported in Node.js. In our V1 release we shifted to Node.js and since last 7 month's we see no lag in any API response, also all our API's are responding in 200-300 Milli Second's with about 8000+ Fleet's in peak hours. So my suggestion is to go with Node.js also you can either go with Mysql or MongoDB ( depending on the usage ) for DB choice's.

When it comes to hosting you can go with group replication which can be replicated across 3 different datacenters for your data safety. This approach will make your system largely scalable at 80% less price then amazon webservcies.

I hope that help's .