Hostnames in backend definition...
phk at phk.freebsd.dk
Wed Dec 14 11:56:17 CET 2011
In message <CB0E33BC.1A17A%mhettwer at team.mobile.de>, "Hettwer, Marian" writes:
>Does varnish cache DNS entries forever and does the dns lookup only once
>at startup time?
>If so, why would it do that?
Varnish does the DNS lookup at VCL compiler time.
This is to avoid DNS-server trouble impacting varnish doing its job.
We have talked about having the health-probe do DNS lookups in the
background, but there are some interesting cornercases that needs
to be dealt with, for instance: What happens when we suddenly get
two IP#'s back, or when we get no ip numbers back.
The advantage to doing the DNS lookup and error checking at VCL compile
time, is that we have a CLI connection to report trouble on.
>The initial DNS answer would include a TTL, indicating how long the record
Yes, and no standardized API returns that TTL to the application
program, so all you can do is call getaddrinfo() periodically, at
whatever frequency you deem appropriate :-(
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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