More tips from @dperjar for a user who specifically asked about using AWS:
You've probably seen that Dropsource integrates with APIs using Swagger/OpenAPI spec. Therefore, the biggest thing to keep in mind when designing and building your API is that it will need to follow REST API principles pretty strictly.
As far as which sort of stack or frameworks we'd suggest... If you have experience in any stack already I'd suggest sticking with it and just following a REST pattern that can be documented with Swagger/OpenAPI spec. If you're starting fresh there are more options. A simple Node.js and Express framework stack is a great place to start. You'd then take that application and run it on an EC2 instance in Amazon. Another good choice we've identified is the Serverless framework. It runs on the AWS Lambda and API Gateway stack. You can use it with multiple languages but we've good success with Node.js. It's unique in that you only pay for what you use and the integration with API Gateway gives you some powerful API management features in addition to being able to export Swagger/OpenAPI inside of the product if you provide some markup.
For databases I'd suggest one of the managed AWS services. I've found DynamoDB fairly easy to work with for a NoSQL solution.