Some time ago I faced a very strange issue with Bind 9 DNS server. Everything was working fine until I rebooted the DNS server. After the reboot server started to return “SERVFAIL” errors instead of resolving the names. It took me more than 2 hours to fix the problem. The problem had been caused by small syntax error in Bind’s zone config file. OK, you can say that that was me who was responsible for the situation. Well, partially, because the changes to the config file had been made many months before I rebooted the server. I remember, that the Bind server did not warn me of any problems while reloading the configuration after I made changes to the zone config file. Moreover, there was no entry in log files about problems with Bind or its configuration either after reloading Bind’s configuration or after rebooting the server.
So, if you make any changes to zone config files for Bind 9 servers make note, that if you do some syntax errors in the config you will not be warned and as the result, the DNS server after the reboot or Bind’s service restart will be unusable constantly throwing “SERVFAIL” errors because it will not be able to load its configuration properly.