Passive health check in stream_proxy module

Roman Arutyunyan arut at
Wed Jun 8 21:46:24 UTC 2016

Hi Frank,

On Tue, Jun 07, 2016 at 04:16:39PM -0700, Frank Liu wrote:
> I checked that page before sending the email.
> The "Passive Health Monitoring" section of that page wasn't clear on how
> nginx would consider a "failed attempt", especially in case of UDP where
> there is no "handshake".
> On Tue, Jun 7, 2016 at 3:45 PM, Yuriy Medvedev <medvedev.yp at>
> wrote:
> > Hi,
> >
> > 2016-06-08 0:03 GMT+03:00 Frank Liu <gfrankliu at>:
> >
> >> How does passive health check work in stream_proxy module? especially for
> >> UDP which is connectionless. How does nginx detect if it is a failed
> >> connection and retry next?

There are two types of such errors.

If proxy_responses is not zero, ICMP Destination Unreachable signals a UDP
error.  This results in socket read error.

If proxy_responses is not default, proxy_timeout expiration is considered a UDP
connection error too.

Roman Arutyunyan

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