wouldn't it be coredns caches the information and records from API server for X amount of time (it seems like this might be 20 minutes?) then once the 20 minutes expired coredns would query api server, receive no response, then fail?
I think the idea of just serving cached responses indefinitely when api server is unreachable is what you're describing but not sure if this is default. (and probably has other tradeoffs that I'm not sure about too)
Based on my understanding of the plugin code it is the default. The way cache.Indexer works is it's continuously streaming resources from APIServer using Watch API and updates internal map. I think if Watch API is down it just sits there and doesn't purge anything but I haven't tested that. The 20 min expiry is probably referring to CodeDNS cache stanza which is a separate plugin[0].
I think the idea of just serving cached responses indefinitely when api server is unreachable is what you're describing but not sure if this is default. (and probably has other tradeoffs that I'm not sure about too)