I'd expect that I would send a Dockerfile once and have that compiled into a lambda for me which would then run in perpetuity unless I sent over a fresh Dockerfile to over-write that deployment, so non-reproducible Dockerfiles wouldn't bother me.
I'm OK with developers needing to understand that a Dockerfile may build differently each time if they don't take extra steps to prevent that (like pinning installed versions etc).
This doesn't seem to me like something that should be a core part of the lambda product, but maybe some sort of simplified build pipeline service that has Lambda as a target.
I'm OK with developers needing to understand that a Dockerfile may build differently each time if they don't take extra steps to prevent that (like pinning installed versions etc).