Not even a caching thing, it's just that Docker images are built by running each step once, in order. If the package is already there for some reason, the whole install step should be removed from the Dockerfile. Basically this is a "runtime" check happening at build time.

I'm a bit confused, any resources you can link with more context?

What I'm confused about:

If the package is already there for some reason, the whole install step should be removed from the Dockerfile

The package already being there depends on install_aws_sdk.sh being run, right? But if the install step is removed from the Dockerfile, isn't it the case that install_aws_sdk.sh will never be run?

Yeah, I'm just saying I think it's fine to assume it isn't being run twice because they would be fairly obvious from looking at the Dockerfiles. But if we were concerned, the right way to do it now would be to use pkg-config to find the library and abort with an error if it exists so the dev can fix in the build.

I think my confusion here is because there's two possible ways to interpret what this condition was for:

1. Preventing the build from compiling the library twice if install_aws_sdk.sh somehow got run twice for a single build
2. Preventing the build from recompiling the library if some build cache was invalidated but this library didn't change

I guess you're saying this wouldn't work for 2, so it's really only about 1. And 1 is probably not an issue because it'd be "fairly obvious", but if it was an issue then the right solution would be pkg-config, not keeping the source files lying around. Right?

Right