mcollective is an orchestration tool created by Puppet Labs that is not specific to Puppet. Plugins exist to work with other configuration management systems. mcollective uses a Message Queue (MQ) tool with active connections from all active nodes to enable parallel job execution on a large numbers of nodes.

To understand how mcollective works, we'll consider the following high-level diagram and work through various components. The configuration of mcollective is somewhat involved and prone to errors. Still, once mcollective is working properly, the power it provides can become addictive. It will be worth the effort, I promise.

In the following diagram, we see that the client executing the mcollective command communicates with the MQ server. The MQ server then sends the query to each of the nodes connected to the queue.

The default MQ installation for marionette uses activemq. The activemq package provided by the Puppet Labs repository is known to work.