During the review of the recent PR to remove use of the init_container from kube pods as created by the Kubernetes back-end, the topic of documenting the "API" for these container images also came up. What information does the back-end provide to these containers? In what form? What assumptions does the back-end make about the structure of these containers?  This information is important in a scenario where a user wants to create custom images, particularly if these are not based on the reference dockerfiles.

A related topic is deciding what such an API should look like.  For example, early incarnations were based more purely on environment variables, which could have advantages in terms of an API that is easy to describe in a document.  If we document the current API, should we annotate it as Experimental?  If not, does that effectively freeze the API?

We are interested in community input about possible customization use cases and opinions on possible API designs!