Localstack is super useful for local (or CI build) development of tech that would be deployed into the cloud. I would definitely not recommend using Localstack for anything in production. I don't think serverless has anything quite as fully featured as what Localstack is able to provide, 1:1 parity across most of AWS's offerings.
I use it for stuff like SecretsManager and Cognito testing (as well as for S3). I don't use it for RDS emulation at all, and just stick a stock postgres container in that spot to achieve local development.
I use it for stuff like SecretsManager and Cognito testing (as well as for S3). I don't use it for RDS emulation at all, and just stick a stock postgres container in that spot to achieve local development.