Actually, code isn't what does that. It's true that code is one of the things that keeps it "all". However, it's not the best place for documentation or even storage of that knowledge. Code changes.

Tests are what you need to invest in. When you test all of you business use cases in an abstract (perhaps even no-code) way, you are truly independent. You can rewrite the system very quickly, if you had a test-suite that allows for quick iteration (TDD style) and does not depend on implementation details.

Given just the code? Well good luck migrating to another cloud vendor. You will probably introduce one million bugs on the way.