Strategies for splitting load across varnish instances? And avoiding single-point-of-failure?

[Michael Fischer]

On Sat, Jan 16, 2010 at 9:22 AM, Poul-Henning Kamp <phk at phk.freebsd.dk>wrote:

> In message <d002c4031001160741q63dd5a50i6342116daba159a6 at mail.gmail.com>,
> Micha
> el Fischer writes:
>
> >On Sat, Jan 16, 2010 at 1:59 AM, Poul-Henning Kamp <phk at phk.freebsd.dk
> >wrote:
> >
> >>        director h1 hash {
> >>                { .backend webserver; .weight 1; }
> >>                { .backend varnish2; .weight 1; }
> >>                { .backend varnish3; .weight 1; }
> >
> >
> >What happens when varnish2 or varnish3 dies?
>
> If a particular backend in the director is unhealthy, the requests
> for it will be redistributed by rehashing over the healthy subset
> of directors.  Once it becomes healthy, normality will be restored.
>
> So everything should work out fine, for some value around 99.9% of fine.


For instance sizes larger than 2, I think a consistent hash is needed.
 Otherwise, the overall hit ratio will fall dramatically upon failure of an
instance as the requests are rerouted.

--Michael
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