[erlang-questions] Force re-resolve of DNS

Roberto Ostinelli roberto@REDACTED
Wed Feb 25 16:31:27 CET 2015

Thank you Geoff,
I'm actually seeing errors way before the 10 minutes.

To put it in perspective: without ELB I can connect 180,000 long-term
connections in 1 minute.
With ELB, I get up to 7,000.

There's the whole "pre-warming" thing so I think this might be related:
though I've been bashing it repeatedly and it really doesn't change
So I'm trying to isolate why this isn't working as expected behind an ELB.

Any thought from anyone who has used ELB in their life? Better if
Erlang-related obviously, this started as an Erlang question after all ;)


On Tue, Feb 24, 2015 at 8:00 PM, Geoff Cant <nem@REDACTED> wrote:

> Looks like {cache_size, 0}. might be an option too.
> That said, ELBs don't change their IPs all that often. It takes ~10mins
> for scale events to happen (increase in requests before the ELB adds more
> nodes), so I wouldn't worry too much about getting dns results to expire
> every minute. I think it's more important that after resolving, if you
> connect and get some kind of error (connection refused, or an invalid ssl
> cert, or some other response that shouldn't be possible from your ELB) that
> your client re-resolves DNS before reconnecting. (i.e. the failure you're
> protecting against is a stale DNS result that's leading you to someone
> else's ELB)
> Cheers,
> -G
> > On 2015-02-24, at 08:26 , Roberto Ostinelli <roberto@REDACTED> wrote:
> >
> > I'm considering using the {cache_refresh, Time}. of inet_cfg:
> > http://www.erlang.org/doc/apps/erts/inet_cfg.html
> >
> > Wouldn't this be a valid option?
> >
> > Best,
> > r.
> >
> > On Tue, Feb 24, 2015 at 4:52 PM, Roberto Ostinelli <roberto@REDACTED>
> wrote:
> > Dear List,
> > I'm currently testing a system behind Amazon's ELB.
> >
> > From their documentation:
> >
> > "If clients do not re-resolve the DNS at least once per minute, then the
> new resources Elastic Load Balancing adds to DNS will not be used by
> clients. This can mean that clients continue to overwhelm a small portion
> of the allocated Elastic Load Balancing resources, while overall Elastic
> Load Balancing is not being heavily utilized".
> >
> > I therefore need to ensure my clients re-resolve the DNS every minute or
> so. Is there a way to do so? I couldn't find anything in inet_res.
> >
> > Thank you,
> > r.
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