Weird backend selection policy

[Sergei Kononov]

Update: removing lookup does not fix this issue at all.

b2 - is a round-robin director with 8 backends specified
rpc - is simple backend, as media

The problem really look like that all the available backends is in
round-robin, request to rpc partially goes to b2 backends and vice
versa. The most strange happened with logs, requests which goes to
wrong backend can't be found neither in varnishncsa.log, nor
varnishlog.

Even running varnishlog -i RxURL,Backend (with out to terminal) does
not show any false backends routes, but clients sees 404 and 500 for
request.

Really, really strange behavior.

On Wed, Mar 25, 2009 at 3:40 PM, Sergei Kononov
<sergei.kononov at gmail.com> wrote:
> Hi,
>
> I noticed weird behavior of backend selection. Some request goes to
> backend which is not suitable for them, as result I getting 404 or 500
> errors, but I noticed that removing "lookup" in end of vcl_recv can
> fix that problem, at least this problem does not occur so frequently
> after that.
>
> Here is my vcl_recv:
>
> sub vcl_recv {
>   set req.http.X-Cacheable = "true";
>   set req.http.X-Forwarded-For=client.ip;
>   set req.backend = default;
>
>   if ( req.url ~ "^/api/.*" ) {
>      set req.backend = b2;
>      set req.url = regsub(req.url, "^/api/", "/")
>      set req.http.X-Cacheable = "false";
>      pipe;
>   }
>
>   if ( req.url ~ "^/rpc.*" ) {
>      set req.backend = rpc;
>      set req.http.X-Cacheable = "false";
>      pipe;
>   }
>
>   if ( req.url ~ "^/flv/.*" || req.url ~ "^/images.(128|320)/.*" ) {
>      set req.backend = media;
>   }
>
>   if ( req.url ~ "^/media.hq.flv/.*" ) {
>      pipe;
>   }
>
>   if ( req.url ~ "^/emit/.*" ) {
>      set req.backend = default;
>      pipe;
>   }
>
>   if (req.http.Cache-Control ~ "no-cache") {
>    pass;
>   }
>
>  #if comment out lookup keyword varnish start to handle requests wierdly
>  #lookup
>  }
>
> And here is my vcl_fetch(not sure that it intended in this issue):
> sub vcl_fetch {
>  if (obj.http.Pragma ~ "no-cache" || obj.http.Cache-Control ~
> "no-cache" || obj.http.Cache-Control ~ "private") {
>   pass;
>  }
>
>  if (! req.http.X-Cacheable ~ "true" ) {
>   set obj.http.Cache-Control = "no-cache";
>   set obj.http.Expires = "Tue, 01 Jan 2000 00:00:01 GMT";
>   pass;
>  }
>
>  set obj.ttl = 3600s;
>
> }
>
> I suppose that there is some error in vlc_ subs, but they seems ok.
>
> --
> Sergei Kononov
>



-- 
Sergei Kononov