Caching OSM tiles - how to not overload backends?

[Xavier Leune]

Hello,

@tranxene50 if implementing a vmod can be very challenging, using haproxy
can be a great solution here. Please refer to this blog post:
https://www.haproxy.com/fr/blog/four-examples-of-haproxy-rate-limiting/ (or
in french ;)
https://www.haproxy.com/fr/blog/four-examples-of-haproxy-rate-limiting/ ).
The very first step is about setting a maximum connections number and a
queuing. Using haproxy as your backend would require low engineering and a
minimum overage.

Regards,

Le lun. 15 juin 2020 à 20:02, Dridi Boukelmoune <dridi at varni.sh> a écrit :

> On Sun, Jun 14, 2020 at 2:32 AM tranxene50
> <tranxene50 at openvz-diff-backups.fr> wrote:
> >
> > Hello!
> >
> > Please forgive my bad English, I live in France.
> >
> > Summary: how to cache - with Varnish - Open Street Map PNG images
> without overloading OSM tiles servers?
> >
> > The question seems related to Varnish backends and ".max_connections"
> parameter.
> >
> > A far as I know, if ".max_connections" is reached for a backend, Varnish
> sends 503 http errors.
> >
> > I understand the logic but would it be possible to queue these incoming
> requests and wait until the selected backend is really available?
> >
> > backend a_tile                  {
> >   .host                         = "a.tile.openstreetmap.org";
> >   .port                         = "80";
> >   .max_connections              = 2;
> > }
> >
> > If Varnish have, let's say 100 incoming requests in 1 second, how can I
> handle this "spike" without overloading the backend?
> >
> > All my google searches were "dead ends" so I think the question is
> poorly formulated.
> >
> > Note 1 : using [random|round_robin] directors could be a temporary
> solution
> > Note 2 : libvmod-dynamic is great but does not limit backend
> simultaneous connexions
> >
> > Many thanks for your help!
>
> Bonsoir,
>
> Unfortunately we don't have any sort of queuing on the backend side,
> so besides implementing your own backend transport from scratch in a
> VMOD there is currently no solution.
>
> Cordialement,
> Dridi
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