Best Local Environments for Developing AWS Lambda Microservices?

I use SAM CLI and LocalStack together. Just a heads up, there's a learning curve with SAM, but once you get the hang of it, it's great for seamless deployments. LocalStack is an option for more comprehensive emulation when necessary, but it's not usually my first choice.

Lambdas are just functions (in languages like JS, Python, or Go), so you can test them like regular functions. There are tools available to help you run Lambdas locally, so firing off HTTP requests against them isn't a big deal.

Start by invoking your Lambda directly with a testing framework instead of worrying about local emulation of API Gateway. You can thoroughly test functionalities like behavior and performance locally. If your Lambda interacts with AWS services, you can choose to use real AWS resources or mock them. A simple way to mock is to create a fake implementation of the services your function interacts with.

What language or framework are you planning to use? Personally, I love using FastAPI along with Mangum. I usually test the FastAPI local HTTP server instead of emulating the full Lambda/API Gateway setup. For smaller projects, I haven't found a reason to complicate things with LocalStack. It's simpler to make sure your setup works locally, so if it needs to change later for Lambda, you can do it relatively easily. There are some quirks with Lambda that might pop up, but they aren't common for smaller applications.

Honestly, I don't bother with emulating AWS services locally. I find it's often more hassle than it's worth. Focus on writing your code to be independent of the environment, so your services can run smoothly whether in a local dev setup or in AWS. Testing in an actual AWS environment can be done quite cheaply, and it ensures you're working in the right context when deploying to production.