The default Docker containers that CodeBuild uses (you can create your own) and the shell script it uses to parse the yaml configuration file (mostly a list of shell scripts) are all open source and the entire process can be run locally.
I agree. I prototyped integrating AWS Lambda into our CI pipeline last year, and was very impressed. Unfortunately, I hit a wall when it came to limiting concurrent executing lambdas (which isn't firecracker's fault),but it was very promising up to then. I'm also curious about using fly.io's machines API [0] for the same thing.
