Now that we have Whirr installed, let's turn our attention toward cluster configuration. Whirr's configuration files, or recipes, are just Java property files that contain Whirr properties which define the layout of nodes and services within a cluster.

Let's start by looking at the minimum configuration necessary to launch a 3-node ZooKeeper cluster:

whirr.cluster-name=zookeeper
whirr.instance-templates=3 zookeeper

The whirr.cluster-name property simply assigns a unique identifier to the cluster and is used when running management commands such as listing the hosts in a cluster or destroying a cluster.

The whirr.instance-template property defines the number of nodes in a cluster and the services that run on each node. In the preceding example, we've defined a cluster of three nodes, with each node assigned with the ZooKeeper role.

With just these two properties defined, we have enough to tell Whirr how to launch and manage a ZooKeeper cluster. Whirr will...