As an occasional user the biggest gripe I have is that credentials are not supported - in our current code base the connection to AWS is done by specifying the region and credentials and leaving the actual endpoint discovery to be done automagically. When using LocalStack you have to instead explicitly specify the endpoint of the service that you want to connect to.

What this means is that if I want to test something locally its not as simply as spinning up the docker container - I also have to make a code modification for the service(s) that I want to interact with.

It's not a big deal - and the benefits of being able to test locally outweigh the minor inconvenience but it still bugs me every time