Build Design - Docker vs Fedora's Mock
Docker is going to be far more well-known than Mock. I consistently see Docker used during build in companies that I work for. I think I have seen Mock before, but only because I am a Fedora user.

However, Docker is not a build tool in of itself, so you can still use Mock inside a container. This is a great way to avoid the "snowflake" build server. By using Docker containers, your builds are consistent no matter what build tool you are using. You can standardise on Docker as a platform for builds, and leave developers to choose the best build tool (whether that's Mock or NPM).

The only other suggestion I'd have is to run the builds on a CI server, and Docker makes this really easy.

Here's one example of a company using Docker for builds (as well as tests and deploys).