With puppet installed, the command /opt/puppet/sbin/refresh-mcollective-metadata is run every 15 minutes. It loggs hostname: Host name lookup failure when it runs.
hostname, hostname -i, and hostname -f all return hostname: Host name lookup failure
This can occur because the hostname is not set in CentOS.
Run the command hostname machine.example.com to set the hostname on the machine then MCollective and all the above-mentioned hostname commands will return the correct values.
Note: it's probably worth looking at the comments on this solution.