Hi Willy,
I never replied to this mail, my apologies!
Thank you for your suggestions. Sadly, in our case, neither approach works
- but it was worth asking you first. I solved our problem with something
that executes right at the start of our application,
Thank you!
Alex
On Wed, Nov 28, 2012 at 7:20 AM, Willy Tarreau <w...@1wt.eu> wrote:
> Hi Alex,
>
> On Tue, Nov 27, 2012 at 11:41:08PM +0000, Alex Davies wrote:
> > Hey All,
> >
> > I have an application that can only handle. to some URLs, one request
> every
> > x seconds from each session (identified by a specific cookie).
> >
> > Rather than adding logic to handle this to the application itself (which
> I
> > fear I will have to do), I would like to know if it is possible to use
> the
> > rate limiting functionality in HAProxy to delay the sending of a request
> to
> > the backend to the time the last request was sent + x fraction of a
> second?
> >
> > I see a bunch of example configs on the internet to reject connections
> over
> > x per second but nothing that queues requests in a order.
>
> If you have just a few such URLs, one thing you could do which will
> approach
> your need is to have a backend per URL (or per group of URL), in which a
> "tcp-request content" rule causes artificially long pauses when the session
> rate is too high. This can work well as long as the number of concurrent
> connections on that backend remains low and known (so that you can adjust
> the timer). If you need only one connection at a time, you could chain
> a server with maxconn 1 to such an installation.
>
> A simple example would consist in this :
>
> frontend front
> use_backend limited if { path_beg /foo /bar }
>
> # limited to 2 requests per second
> backend limited
> tcp-request inspect-delay 500
> tcp-request content accept if { be_sess_rate le 2 } || WAIT_END
> server ...
>
> This can work well for printing devices or PDF generators for example.
> It won't work well at all if you don't know the number of concurrent
> users, in which case it could be done like this (even uglier) :
>
> frontend front
> use_backend serialize if { path_beg /foo /bar }
>
> # serialize requests
> backend serialize
> server limited 127.0.0.1:1 maxconn 1 send-proxy
>
> # limited to 2 requests per second
> listen limited
> bind 127.0.0.1:1 accept-proxy
> tcp-request inspect-delay 500
> tcp-request content accept if { be_sess_rate le 2 } || WAIT_END
> server ...
>
> This time it will do the job whatever the number of concurrent clients.
> But it's not very pretty...
>
> Willy
>
>
--
Alex Davies
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