Hello,

On Wed, Nov 27, 2019 at 10:25 PM Willy Tarreau <w...@1wt.eu> wrote:
>
> Hi Marco,
>
> On Wed, Nov 27, 2019 at 08:38:03AM +0100, Marco Corte wrote:
> > Hello!
> >
> > I see a strange behaviour of the DNS resolution on version 2.0.9 and 2.0.10,
> > but I do not know since when this happens.
> >
> > On Ubuntu 18.04, I set up haproxy to use the local DNS service provided by
> > systemd.
> > Actually I see that haproxy tries to resolve the names every second.
> > The resolution is successful, the TTL in the answer is 1800s or longer.
>
> It's the interval of your server checks. The resolution is sent at the same
> frequency as the checks. The reason is that in environments using dynamic
> server addresses, you definitely need to check your address at the same
> frequency you care for the server's availability. In addition, in some
> fast-recycling environments (AWS used to be like this, I don't know if
> it's still the case), when you shut down your server, it was possible that
> its IP address was reassigned so fast that the server didn't even have the
> time to appear dead, and the traffic could continue to be delivered to
> someone else's server!
>
> If it bothers you (I don't really see why), you can increase the "inter"
> value on your servers to check them less often and as such refresh their
> address less often.

You can configure "hold valid <time>" to configure internal caching
(it should be 10 seconds by default though):

https://cbonte.github.io/haproxy-dconv/2.0/configuration.html#5.3.2-hold



Lukas

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