Coredns: middleware/cache: Prefetch entries

[SuperQ]

Feature proposal:

Add a prefetch feature to the cache. This allows for cached records to be updated before the TTL expires. This is useful to avoid empty cache records for frequently used DNS-based service discovery records.

[miekg]

Excellent idea. Note that cache is relative standalone, so the trick here will be: with what mechanism will the cache be refilled?

[miekg]

While talking with @stp-ip at KubeCon we somewhat settled that we should implement this in the caching middleware, i.e. add a proxy stanza to allow prefetch.

We also need to tell it when a record is 'hot' and should be prefetched, before the TTL expires. Popular might be defined as: x queries/minute.
~
prefetch ADRESS... {
threshold 5 # meaning 5 requests seens in the last minute
}
~
And have threshold be some kind of default, so prefetch ADDRESS.. will work as well.

[miekg]

Don't think we can fix this in time for 007 release (want to do that this month). Bumping to 008

[miekg]

I'm hoping to work on this, this week, in time for the 008 release.

[SuperQ]

Looks like this made it into 008. 🎉