the hash director will fail if all the backends are failing. if you
define a random director with the same set of backends, and if the hash
director fails, the random director fails too?
kt
On Mon, Aug 01, 2011 at 05:44:01AM +0000, Thiago Figueiro wrote:
> Hi, all.
>
> I'm experimenting with the hash director but the current documentation[1] is
> brief and I need some help. (background: our application servers do some
> local fragment caching and this is more efficient if the URLs go to servers
> which already have the necessary fragments).
>
> As desired, the hash director is selecting the same backend for a given URL.
> However, when the backend goes sick, I expect varnish to pick a healthy one;
> instead I get a 503 due to no backend available.
>
> This is the backend definition:
>
> director example hash {
> .retries = 5;
> { .backend = server1; .weight = 1; }
> (...)
> { .backend = server8; .weight = 1; }
> }
>
> I assumed the "retries" parameter in the director definition would try
> different backends; it might be that it retries the same backend.
>
> It could be relevant that my vcl_fetch has:
>
> sub vcl_fetch {
> (...)
> # If status not one of the below try again (up to max_restarts)
> if (
> beresp.status != 200 && beresp.status != 403 && beresp.status != 404
> &&
> beresp.status != 301 && beresp.status != 302 && beresp.status != 307
> &&
> beresp.status != 410) {
> if (req.http.X-Forwarded-Host) {
> set req.http.Host = req.http.X-Forwarded-Host;
> }
>
> restart;
> }
>
>
> To overcome this I thought about defining a random director with the same set
> of servers and, should the hash director fail, I'd update req.backend to use
> the random director. I don't like this too much because it would double the
> number of health checks, which are not exactly cheap, and I would need to
> complicate the VCL a bit more.
>
> Am I missing something? Is there a better way of handling this situation?
>
>
> Thanks.
>
>
> [1]
> https://www.varnish-cache.org/docs/2.1/reference/vcl.html#the-hash-director
> ?
>
> Thiago Figueiro
> Technical Operations Manager
>
> Westfield Digital Business
> T +61 (0)2 9358 7123
> M +61 (0)405 700 814
> W www.westfield.com.au
> E [email protected]
>
>
>
>
>
>
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