Chapter 9. Fabric Ensemble and Registry

Abstract

The Fabric ensemble and registry is a critical part of the Fabric infrastructure. In a production environment, it is particularly important to understand the correct approach to creating and maintaining a Fabric ensemble.

9.1. Fabric Registry

Overview

Fuse Fabric uses Apache ZooKeeper (a highly reliable distributed coordination service) as its registry for storing cluster configuration and node registration.
ZooKeeper is designed with consistency and high availability in mind, while protecting against network splits, using the concept of a server quorum. For example, you might run five ZooKeeper servers and, so long as you have a quorum (three or more servers available), the ZooKeeper cluster is reliable and not in a network split.

Registry structure

The structure of the registry is a tree-like structure, similar to a filesystem. Each node of the tree (a znode) can hold data and can have children.
For example, the following shows an outline of the registry structure:
        fabric
            |
            +----registry (runtime registry)
            |        |
            |        +----containers
            |                 |
            |                 +----root
            |
            +----configs (configuration registry)
                     |
                     +----versions
                     |        |
                     |        +----1.0
                     |               |
                     |               +----profiles
                     |                        |
                     |                        +----default
                     |
                     +----containers

Parts of the registry

Conceptually, the Fabric registry consists of two main parts:
  • Configuration Registry—the logical configuration of your fabric, which typically contains no physical machine information. It contains details of the applications to be deployed and their dependencies.
  • Runtime Registry—contains details of how many machines are actually running, their physical location, and what services they are implementing.

Making the registry highly available

With a single container hosting the registry, high availability is not supported. In order to have a highly available Fabric registry, you need to replicate the registry on multiple containers (on different physical hosts). The common term used to describe a group of servers that replicate the Fabric registry is an ensemble.