Sorry I missed this, updated the description

** Description changed:

+ [Impact]
+ 
+ Currently, when there is an update for the bind9 package, and bind's
+ configuration is wrong/outdated is some way, then a production DNS setup
+ could be taken out when named fails to restart.
+ 
+ This should be backported to stable releases to avoid named failures
+ during SRUs and upgrades between Ubuntu versions.
+ 
+ This issue is handled by running named-checkconf during the upgrade to
+ confirm named.conf is valid prior to the named restart.
+ 
+ [Test Plan]
+ 
+ To test the issue, edit /etc/bind/named.conf to be invalid, such as
+ including a nonexistant file:
+ 
+ include "/etc/file-that-does-not-exist";
+ 
+ Then update bind9 to a new version, and confirm the postinst breaks
+ prior to restarting named.
+ 
+ [Where problems could occur]
+ 
+ Problems could occur during the postinst process. When named-checkconf
+ fails, the installation stops. If it were incorrect in its failure, then
+ the installation would be blocked unnecessarily. Also, if named-
+ checkconf were to be excluded from bind9's dependency tree, then the
+ upgrade would also fail.
+ 
+ [Other Info]
+  
+ This fix is available in questing through the debian version 1:9.20.8-5. It 
is being backported alongside new version updates for bind9 this cycle - LP: 
#2112520
+ 
+ [Original Description]
+ 
  We recently had a bind9 package upgrade take out DNS services for a
  production cloud because named failed to come up after the postinst
- restarted it.  So obviously, a) our DNS shouldn't be a SPOF and b) we
+ restarted it. So obviously, a) our DNS shouldn't be a SPOF and b) we
  shouldn't let our config files get into a state where named refuses to
  start, but, with that said, the bind9 postinst could be more robust
  against this kind of failure mode.
  
  Specifically it could run named-checkconf against /etc/bind/named.conf
  and, if it returns 1, either:
  
   a) skip the restart and scream loudly to warn the admin
  
  or
  
   b) abort the package install by erroring out of the postinst at that
  point

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https://bugs.launchpad.net/bugs/1492212

Title:
  postinst should validate config before restarting bind

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