Getting started with CFEngine part 1 (The basics)

This quick start guide is based on my understanding CFEngine concepts & working.

I've tried to make it as understandable & precise as I could.

CFEngine is a configuration management & automation tool that has been around since the 90s.

It works on a variety of UNIX platforms as well as Windows.

Some of its features are:

Ensures systems have self-healing capabilities.

Convergence of systems to reach a desired state of configuration

Some low level examples include:

•  Build new nodes
• Deploy & manage services & applications
• Managing databases
• Manage ACLs

                                                                                                  

Components of CFEngine:

Cf-agent

Cf-monitord

Cf-execd

Cf-serverd

In CFEngine a desired state configuration of nodes is reached via implementation of policies.

Server-client architecture:

CFEngine is based on a server-client architecture wherein the cf-agent running on the client communicates with the cf-serverd daemon on the server (hub) for policy updates every 5 minutes.

The next part introduces some key terms used in writing configurations to be executed by CFEngine.

Promise Theory:

A Model of voluntary cooperation between individual agents who publish their intentions to one another in the form of promises.

Files & processes can make promises about their contents.

A process can make a promise to be in running state but cannot make a promise regarding its configuration.

Anatomy of a promise:

type:

 context::

       "promiser" -> "promisee"

         attribute => "value";

In the above example:

type can be files or commands.

context is a condition deciding where & when to execute the promise.

promiser is the file or process making the promise.

attribute details & constrains a promise.

Bundles:

A bundle is a logical grouping of promises that are written with the aim of achieving a common end goal. For example promises written to install, configure & start MySQL.

Anatomy of a bundle:

bundle type name{

type;

 context::

       "promiser" -> "promisee"

         attribute => "value";

}

Bundles apply to the binary that executes them. Agent bundles apply to cf-agent.

Body:

A body is a collection of attributes.

Anatomy of a body:

body type name{

         attribute1 => "value";

         attribute2 => "value";

}

In a body every attribute ends with a semi colon.

The components discussed above come together in the form of a plain text file with .cf extension called a policy.