9.3. Definitions

See Message Bus.
Finite State Machine (FSM)
Javascript Object Notation. Data which can be turned into code. Usually returned from REST APIs. It’s also called a data interchange standard.
Message Bus
Very similar to how the postal service works, but in software. Clients connect to the bus and consume or publish messages. It’s like IPC, over the network, with queues, on steroids.

A “schemaless” document object collection.

Basically MySQL without all the rigidly defined table structures.

A document describing a software release. This document is stored in MongoDB. Playbooks consists of three main items: ownership identification, target hosts, and a list of steps (See also: Playbook Step) required to finish so that the release can be considered completed.
Playbook Step

A playbook step represents a unit of work in your overall release process.

Defining a playbook step is like instantiating a Worker Plugin. That is to say, using the api signature of a given Worker Plugin, you fill in the missing parameters.

The programming language the Release Engine is primarily written in.
The re-client tool is how end-users primarily interact with the release engine. The re-client tool interfaces with the RE-REST component and provides several options for creating, reading, updating, and deleting playbooks.
The ring-leader of the system. Orchestrates the delegation of playbook steps to worker plugins. Tracks the state of a release in mongo and manupilates the completed/active/remaining job stacks as workers update the FSM.

A REST endpoint (see below) which all clients attempting to interact with the Release Engine must proxy their commands and requests through. This component in integrated into the overall authentication/authorization scheme.

Authorized requests made against the REST endpoint result in either: messages having been sent to the RE-CORE component (for example: begin a release for group foo), or in database create/relad/update/delete operations.

Representational State Transfer. Using the HTTP protocol in a programmatic way to interact with remote systems. Usually supports the basic CRUD operations: Creating, Reaing, Updating, and Deleting records.
Temporary Queue
(See also: Message Bus) Temporary queues are created by various Release Engine components. These queues are ephemeral and usually automatically clean themselves up after all clients disconnect from them. The purpose of these temporary queues is to enable direct communication between two specific components, outside of the pre-defined channels of communication.
Worker (Plugin)

Worker plugins do the actual work in a release. This could mean several things: running puppet on a server; restarting a host; uploading RPMs into a YUM repository, scheduling downtime, the possibilities are virtually endless.

It might help to think of Worker Plugins as Class definitions. See Playbook Step for the other half of that comparison.

YAML Ain’t Markup Language. YAML is an alternative syntax which may be used to write Playbooks in. The normative syntax is JSON.

See also

YAML Basics
Introduction to YAML formatting

See also

Everything you need to know to begin writing playbooks