Using an external node classifier

When Puppet runs on a node, it needs to know which classes should be applied to that node. For example, if it is a web server node, it might need to include an apache class. The normal way to map nodes to classes is in the Puppet manifest itself, for example in a nodes.pp file:

node 'web1' {
  include apache
}

Alternatively, you can use an external node classifier to do this job. An external node classifier (ENC for short) is any executable program which can accept a node name and return a list of classes which should be applied to that node.

An ENC could be a simple shell script, for example, or a wrapper around a more complicated program or API that can decide how to map nodes to classes. In this example we'll build the most trivial of ENCs, a shell script which simply prints out a list of classes to include.

Getting ready...

An ENC has certain restrictions compared to a node declaration: for example, you can't declare individual resources, but can only include...