Is it possible to monitor the fair proxy balancer?

[Alexander Staubo]

On Sat, Jun 28, 2008 at 2:31 PM, Grzegorz Nosek
<grzegorz.nosek at gmail.com> wrote:
> However, there still remains the issue of communication between the load
> balancer and the outside world, i.e. *how* would you like to be told
> that a backend has been deemed up/down

HAProxy -- apologies for having to mention it again, but it's a useful
template -- has a simple status page similar to Nginx's stub status.
It comes in HTML and CSV formats, and lists all backends (and
frontends) and their status (up, down, going down, going up) and a ton
of metrics (current number of connections, number of bytes transfered,
error count, retry count, and so on). It can also export the same
information on a secure domain socket if you don't want to go through
HTTP.

> and *how* would you like to tell
> nginx that backend 1.2.3.4 is currently down?

Pardon me for asking a naive question, but to change the list of
backends, would you not simply edit the config file and do a SIGHUP? I
would reset whatever internal structures that are kept by the workers,
but I can't think of anything that's not okay to lose.

>  - a new option, e.g. max_requests 10 10 20 20 (specifying the number
>   for each backend in the order of server directives)

That's a horrible syntax and one that is going to cause problems as
you add or remove backends from the config. A max_requests setting
belongs on each backend declaration.

> So, what say you, is such a feature (amounting to returning 502 errors
> after a certain amount of concurrent requests is reached) generally
> desired? If so, how would you like to configure it?

You should only return an error if a request cannot be served within a
given timeout, not when all backends are full.

Alexander.