Hash director and backend health

Thiago Figueiro TFigueiro at au.westfield.com
Mon Aug 1 08:34:37 CEST 2011

KT Sin wrote:
> 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?

That's not what I'm seeing in my tests.

I have 8 servers in the hash director and I only took 1 of them offline, the one a test URL resolves to.  If I request a different URL I get a response; if I request the URL that goes to the offline server I get 503.

Here are some successful log entries:
   53 RxURL        c http://www.westfield.com.au/au/?thiago-1
   53 Backend      c 42 centre_rails centre_rail_ausyd_fap05
   46 RxURL        c http://www.westfield.com.au/au/?thiago-2
   46 Backend      c 41 centre_rails centre_rail_ausyd_fap04

If I take fap05 offline and try both URLs again I see an error:
   46 RxURL        c http://www.westfield.com.au/au/?thiago-1
   46 FetchError   c no backend connection
   46 TxStatus     c 503
   42 RxURL        c http://www.westfield.com.au/au/?thiago-2
   42 Backend      c 41 centre_rails centre_rail_ausyd_fap04

So "thiago-1" goes to fap05 and "thiago-2" goes to fap04.  If I stop fap05, I get "FetchError" for "thiago-1", however "thiago-2" responds normally.

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