[Varnish] #369: Enable serving of graced objects if backend is down

[Varnish]

#369: Enable serving of graced objects if backend is down
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 Reporter:  perbu        |        Owner:  phk  
     Type:  enhancement  |       Status:  new  
 Priority:  normal       |    Milestone:       
Component:  varnishd     |      Version:  trunk
 Severity:  normal       |   Resolution:       
 Keywords:               |  
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Comment (by anders):

 We (Aftenposten & E24) are interested in helping sponsor this feature,
 provided that:

 1) Forced grace always will work for any kind of backend error (network
 timeout, connection refused, response too slow, wrong http return code)

 2) It works with a longer grace period, so that the backlog of cached data
 is longer. This shall not create problems for updates/purges for new
 content.

 3) It is possible to control in VCL when forced grace should happen. For
 example if the backend delivers an unwanted 5xx http return code.

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Ticket URL: <http://varnish.projects.linpro.no/ticket/369#comment:4>
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