Follow CNAME and DNAME records

[mreiger]

Hi @GrigoriyMikhalkin can you have a look at what I am trying here and tell me if this is a valid approach? (Following the CNAME redirection with recursive DNS lookups)

Im still a bit concerned if this works as intended; in a test I got a name with multiple CNAME redirections resolved even though there were more redirection levels than the TTL I built into the recursive lookup. Also the code is at least somewhat ineffective: Usually the resolution of CNAME to A record comes in the same reply but this is currently ignored and a recursive DNS query vor the CNAME is done anyway.

So @chbmuc: I'd like to resolve these issues before I declare it ready for review.

[mreiger]

I think this is ready to look at now. Couple thoughts though:

• We probably should turn the logging down to a reasonable amount before releasing this though
• I wonder if we could use a context to break the recursion once the redirection TTL has been reached; but I'm not sure where to get the context from.

Concerning DNAME: This seems to indicate that there's always a CNAME returned as well, so it may not be necessary to handle DNAME records separately.

[Gerrit91]

From the code perspective I do not really understand it and I find it hard to read, but it's passing the integration tests and if you say it works, we can put this into the release.