[Varnish] #797: VCL error on non existing DNS backend

[Varnish]

#797: VCL error on non existing DNS backend
------------------------+---------------------------------------------------
 Reporter:  gdelacroix  |       Owner:  phk                 
     Type:  defect      |      Status:  new                 
 Priority:  high        |   Milestone:                      
Component:  varnishd    |     Version:  2.0                 
 Severity:  major       |    Keywords:  vcl backend DNS name
------------------------+---------------------------------------------------
 Hi!
 I've found that Varnish is sending a VCL error when a backend leads to a
 DNS name that doesn't exists.

 Example :
 Here is a DNS name that doesn't exists :
 {{{
 backend= {
   .host = "www.fu.bar";
   .port = "80";
 }
 }}}

 Here is the error I get :
 {{{
 Message from VCC-compiler:
 Backend host '"www.fu.bar"': Name or service not known
 (input Line 113 Pos 17)
         .host = "www.fu.bar";
 ----------------############-

 In backend host specification starting at:
 (input Line 112 Pos 17)
       .backend= {
 ----------------#
 }}}

 I think it's a big behavior issue because it is possible to compile, and
 run in production, a VCL config leading to an existing DNS name, that
 could disappear in the future, and then cause Varnish being unable to
 restart because of VCL error.

 I think the only viable behavior would be removing DNS check (knowing that
 there's no IP check for IP backends).

 I'm running Varnish 2.0.6 (and not able to switch to 2.1 because of
 backend handling removal in varnishncsa).

 Best regards.

 Gauthier Delacroix
 Pictime

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Ticket URL: <http://varnish-cache.org/trac/ticket/797>
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