Multi tenant implementation

This depends on how you want to set this up. If you use a cloud provider, they have their own APIs to manage the infrastructure. The example above that I gave is also not an efficient solution, but merely a proof of concept. There is a lot of know-how from different disciplines that goes into creating - and maintaining - a commercially viable solution.

That is not to discourage you. You could start with a simple proof of concept and go from there as you identify bottlenecks along the way. Keep in mind that the know-how required goes beyond this forum and is in many aspects not related to Parse Server specifically.