This subcommand eases the debugging of external-data-driven Puppet templates by fetching the External Node Classifier output from the exec terminus but modifying the list of classes to a user-specified subset.

As we move towards better separation between data and code, especially for complex templates, the distance between manipulating the data and observing the results of the manipulation can become quite wide. In my environment, we make heavy use of external node classifier variables to define template values, which is quite powerful, but imposes workflow like:

modify ENC database values ->
modify puppet code ->
check in puppet code ->
update test puppet master ->
run client against test master

This can make it slow to iterate quickly when testing new changes. puppet-minicat is meant shorten the cycle, by allowing someone working on a template to consult the node classifer as if they were the real end client, generating
just the subset of the catalog that contains the class they're working on, and printing that catalog out in text format instead of trying to actually apply it.

To use puppet-minicat, simply download the module and adjust your RUBYLIB environment variable to include the module's lib/ subdirectory. running puppet help should show you the one-line help text for minicat along with the other faces, and puppet man minicat should show the complete help text.

In actual usage, I found it helpful to create a small puppet.conf which sets the modulepath, node_terminus and external_node config variables. The external_node script can simply return the output from the node classifier for the node we're interested in, or, if you already have a web-service-accesible node classifier, it can return the actual output. In the latter case, the --node argument to puppet minicat will let you specify the node whose data should be requested.

A typical command line looks like this:

puppet minicat compile --debug --config ./etc/puppet.conf --node puppetmaster.domain.com \
   --classlist puppet::master::environments --modulepath=/Users/eric/Sandbox/puppet-config/trunk/modules 

This fetches the node classifier information for puppetmaster.domain.com and uses its parameters: section to compile a catalog containing only those resources in the puppet::master::environments class, using my working copy changes to the puppet modules. The output is a screenful of json which contains the thing I'm most interested in debugging: a template-ized puppet.conf which uses node classifier data to set up an \[environment\] stanza for each of the test branches.

Puppet 2.7.x is required to use the Faces API.

Minicat uses Awesome Print for pretty-printing the catalog data structures and YAJL ruby to pull the catalog back into a data structure that AP can deal with.

The code lives at puppet-minicat, please feel free to fork and file issues or pull requests there.