Dual server Varnish setup

[Laurence Rowe]

You'd be better off using the random director for cr-backends as each
varnish defines the director.

For the varnishes, you probably don't want to use a director, but
check the next varnish in the ring. Requests to another varnish should
be much cheaper than going to the backend, and you want to fill up
each varnish as you go around to minimise backend requests.

sub vcl_recv {
   set req.backend = next_varnish;
   # Keep a unary count of how many varnishes this request has been through
   if (!req.http.X-Via-Varnish) {
       set req.http.X-Via-Varnish = "1";
   } else {
       set req.http.X-Via-Varnish = req.http.X-Via-Varnish "1";
   }
   if (req.http.X-Via-Varnish ~ "1111" || !req.backend.healthy) {
       # Request is coming from the other server.
       set req.backend = cr-backends;
   } else {
       set req.http.X-Via-Varnish = "true";
   }
}

This is more complex than a pair though, so not sure what you want to
do about the hash_ignore_busy here.

Laurence

On 10 February 2011 16:37, Ben Dodd <B.Dodd at comicrelief.com> wrote:
> Something like this:
>
> director cr-backends round-robin {
>  .retries = 5;
>
>  {
>    .backend...
>  }
>
>  # Repeat the above entry for each web server.
> }
>
> director cr-varnish round-robin {
>  .retries = 4;
>
>  {
>    .backend...
>  }
>
>  # Repeat the above entry for each varnish server.
> }
>
> sub vcl_recv {
>
>  set req.backend = cr-varnish;
>
>  if (req.http.X-Via-Varnish || req.restarts > 3) {
>    # Request is coming from the other server.
>    # Ignore busy objects to avoid race condition.
>    set req.hash_ignore_busy = 1;
>    set req.backend = cr-backends;
>  } else {
>    set req.http.X-Via-Varnish = "true";
>  }
> }
>
> Thanks, Ben
>
> On 10 Feb 2011, at 14:14, Martin Boer wrote:
>
>> I would also add weights so that each varnish prefers to ask its sibling
>> say 250 times more often than asking the app-server.
>> This will ensure that both varnishes will be as filled and as equal as
>> possible.
>> I don't know if 250 could be replaced by a larger number but this works
>> for me.
>>
>> Regards,
>> Martin
>>
>> On 02/10/2011 02:46 PM, Laurence Rowe wrote:
>>> On 8 February 2011 23:05, Ben Dodd<B.Dodd at comicrelief.com>  wrote:
>>>> Given this functionality, does anyone know what the VCL is required to implement this dual server Varnish setup scenario?
>>>> http://varnish-cache.org/trac/wiki/VCLExampleHashIgnoreBusy
>>> Something like this should work:
>>>
>>>
>>> backend appserver { ... }
>>> backend other_varnish { ... }
>>>
>>> # Server 1
>>> sub vcl_recv {
>>>     set req.backend = other_varnish;
>>>     if (req.http.X-Via-Varnish || !req.backend.healthy) {
>>>         # Request is coming from the other server.
>>>         # Ignore busy objects to avoid race condition.
>>>         set req.hash_ignore_busy = 1;
>>>         set req.backend = appserver;
>>>     } else {
>>>         set req.http.X-Via-Varnish = "true";
>>>     }
>>> }
>>>
>>> # Server 2
>>> sub vcl_recv {
>>>     set req.backend = other_varnish;
>>>     if (req.http.X-Via-Varnish || !req.backend.healthy) {
>>>         # Request is coming from the other server.
>>>         set req.backend = appserver;
>>>     } else {
>>>         set req.http.X-Via-Varnish = "true";
>>>     }
>>> }
>>>
>>> Laurence
>>>
>>> _______________________________________________
>>> varnish-misc mailing list
>>> varnish-misc at varnish-cache.org
>>> http://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc
>>>
>>>
>>
>>
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