Often in a Puppet manifest, you need to know some local information about the machine you're on. Facter is the tool that accompanies Puppet to provide a standard way of getting information (facts) from the environment about things such as these:
Operating system
Memory size
Architecture
Processor count
To see a complete list of the facts available on your system, run:
$ sudo facter architecture => amd64 augeasversion => 0.10.0 domain => compute-1.internal ec2_ami_id => ami-137bcf7a ec2_ami_launch_index => 0
Note
While it can be handy to get this information from the command line, the real power of Facter lies in being able to access these facts in your Puppet manifests.
Some modules define their own facts; to see any facts that have been defined locally, add the -p (pluginsync) option to facter as follows:
$ sudo facter -p