How to add validation to reusable modules?

[adecusati]

I am using the Kubernetes module. I would like to add validation to metadata. One approach I can think of would be to override the ObjectMeta schema to add the checks. However, in complex objects, metadata may appear at multiple levels (ex. Deployment metadata and pod template).

I was looking at Rules, but I am not sure I understand how they are meant to be used. All the examples basically check root level values, but how would I apply rule checks in nested structures? What is the context of their execution, for example, if i run them in a Schema check? How would I use them in a mixin (if i can)?

In general, I struggle to understand the differences between protocol/schema/mixin/rule. I feel like the docs could use better examples that combine these together and demonstrate clear use cases for each. These concepts could probably use their own section.

They all seem similar, but with different constraints. I get the concepts, but struggle with the details - like when should i use one vs. another? What is an example that uses all of them all together?

[Peefy]

cc @zong-zhe @He1pa