The gist is that tags are mutable and deletable. Local caching means that every node can disagree on what the tag resolves to, and so can the registry. What version corresponds to which tag at which location at a given time is not deterministic.
The only way out is to use fully-digested references. The digest means that there can be no mutation of what's being pointed to. It will mean the same in every configuration and on every node, no matter when the reference is resolved and no matter when the reference was created.
It also means every layer has to be kept indefinitely, forever. Tags at the very least are pointers that stop indefinite and exponential storage growth.
Tags don't help exponential growth, because you cannot reliably reason from a tag-only reference back to the exact assets it represents. That's feasible with fully-digested references.
The relevant section is here: https://livebook.manning.com/book/knative-in-action/chapter-...
The gist is that tags are mutable and deletable. Local caching means that every node can disagree on what the tag resolves to, and so can the registry. What version corresponds to which tag at which location at a given time is not deterministic.
The only way out is to use fully-digested references. The digest means that there can be no mutation of what's being pointed to. It will mean the same in every configuration and on every node, no matter when the reference is resolved and no matter when the reference was created.