EC2 vs. Lambda for API: Which One Should I Choose?

EC2 gives you full control as it's a server you manage, so its performance ultimately depends on how you configure it. Lambda, on the other hand, is super handy as it automatically scales for you. For your MongoDB connections, it's best to set up your db connection outside the main function to reuse it for subsequent requests. And don’t stress too much about race conditions; each Lambda function runs in an isolated environment, but if two users try to order the last item at the same time, there could be issues unless you handle that in your logic.

It really depends on the setup of your EC2 instance. For a simple CRUD application, even a smaller instance like a t4.small can manage tens of concurrent requests, maybe even hundreds. One thing to keep in mind with Lambda is that although it can scale up easily, each cold start can take a bit longer, usually around 100-300ms. Don’t forget, managing your own server on EC2 means you also handle maintenance and updates, which is quite different from the hands-off approach with Lambda.