Every time puppet is run, it sends an info message about adding aliases to every host with an alias. This happens even when the alias already exists, but should only happen the first time.
puppettest:~# grep example /etc/hosts
puppettest:~# puppet -v /tmp/test.pp
info: Loading fact virtual
info: Loading fact kernelversion
info: /Host[test.example.com]: Adding aliases "test"
notice: /Host[test.example.com]/ensure: created
info: Filebucket[/var/lib/puppet/clientbucket]: Adding /etc/hosts(91412413d215f23fab736c74e22ef2e4)
puppettest:~# grep example /etc/hosts
10.0.0.1 test.example.com test
puppettest:~# puppet -v /tmp/test.pp
info: Loading fact virtual
info: Loading fact kernelversion
info: /Host[test.example.com]: Adding aliases "test"
puppettest:~# grep example /etc/hosts
10.0.0.1 test.example.com test
puppettest:~# puppet -v /tmp/test.pp
info: Loading fact virtual
info: Loading fact kernelversion
info: /Host[test.example.com]: Adding aliases "test"
puppettest:~# cat /tmp/test.pp
host { "test.example.com" :
ip => "10.0.0.1",
alias => "test",
ensure => present,
}