pdns_server reports zone is temporarily not available

Symptoms

After modifying a zone, attempts to use dig to view the zone result in the following:

;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 12345

When looking in /var/log/messages, you see:

Jun 11 11:23:58 hostname pdns_server: Backend reported condition which prevented 
lookup (Zone for 'example.com' in '/var/named/example.com.db' temporarily not 
available (file missing, or master dead)) sending out servfail

Description 

This means that for some reason, PowerDNS cannot read the zone file.  In the case that spawned this article, this was because the file was owned by root:

-rw------- 1 root root 2.0K Jun 11 10:25 /var/named/example.com.db

Fix

To fix this issue, there were two steps necessary.  First, to update the ownership on the file to named, which is the user that PowerDNS runs as.  Second, to reload the zone so that PowerDNS was aware of the update.  These steps can be done with the following commands:

chown named:named /var/named/example.com.db

and

pdns_control bind-reload-now example.com