How to host Node.js Auth service, Match service, Chat service with MongoDB, Neo4j, PostgreSQL, Redis, RabbitMQ?

We’re planning on using a similar structure to you. Be great to understand your thought process behind this structure.

You mention you have an NGINX in front, I presume this is acting as the API gateway which then points to the differing services? Or is this load balancing with a different Node server as the API Gateway?

In terms of chat vs auth services, would it not be better to swap round the types of databases? I would have thought a nosql like MongoDB would be better suited to chat/social media and similarly with Postgres for the Auth service?

I would recommend setting this up with 5 small droplets as this will provide you more options when it comes time to scale up. Your RabbitMQ can communicate between services over the private network so it’s communications wouldn’t count towards your bandwidth limits.

Starting out with the services and their associated DB on the same server will provide a less expensive deployment and once you begin to really scale you can set up dedicated DB servers to reduce the load on your app droplets.