Hello!

On Fri, Aug 10, 2012 at 01:36:46PM +0200, Axel wrote:

> Hello all,
>
> i'm new to nginx and first of all i have to say it's a great piece
> of software.
>
> I need some more detailed Information about nginx behaviour
> regarding HttpUpstreamModule and I hope you can give me some hints
> and links where i can learn more about it.
> I set up nginx/1.2.2 as reverse proxy in front of a bunch of apache
> server(*) which are located in different housing locations.
>
> Now I have some questions and I can't find any docs or wiki pages
> with detailed answers.
>
> - how does nginx detect if one ore more upstream servers has diappeared?
> - what kind of mechanism does nginx use? icmp or something else?

It detects based on status of requests to upstream servers. If
requests fail - the server is considered down and additional
requests aren't routed to it for some time.

http://nginx.org/en/docs/http/ngx_http_upstream_module.html#server

> - how often does nginx request the status of upstream servers?

For alive servers - as often as normal requests are routed to the
servers. For servers already considered down - once per
fail_timeout (per worker, see below).

> - how can I monitor the status of upstream server seen by nginx (I
> monitor the status of running apache prcesses on the upstream server
> separately)

Currently, there is no way. Moreover, each nginx worker process
has it's own idea about status of upstream servers.

Maxim Dounin

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