At its core, CFEngine is a simple framework which supplies a rich standard library of tools to implement and manage very large systems. The following diagram captures the scope of CFEngine.
For many users, CFEngine is simply a configuration tool – i.e. software for deploying and patching systems according to a policy. Policy is described using promises. Every statement in CFEngine 3 is a promise to be kept at some time or location. More than this, however, CFEngine is not like other automation tools that "roll out" an image of some software once and hope for the best. Every promise that you make in CFEngine is continuously verified and maintained. It is not a one-off operation, but a process that can repairing itself should anything deviate from the policy.
That clearly places CFEngine in the realm of automation, which often begs the question: so it's just another scripting language? Certainly, CFEngine contains a powerful scripting language, but it is not like any other. CFEngine language is a declarative language of promises, in which you express very high-level intentions about a system. CFEngine then takes the promises and compiles them into real-world action.
Ready to Start?
If you are impatient to get started writing promises, now might be a good time to take a break from concepts and try out your first promises. You can study the examples and look things up in the reference as you go along.