1.3. Provisioning and Configuration

Each node in the cluster has a logical name and on startup the provisioning agent registers an ephemeral node in ZooKeeper. It then looks in the configuration using its logical name for its profile of what configuration to use and what services to provision. If there is no configuration or the logical name it uses the default profile.

Each node watches the relevant parts of the ZooKeeper tree for changes; so that as soon as any profile is updated the dependent nodes refresh and re-apply any provisioning or configuration changes.

You can use the Fabric command line shell to modify a profile's configuration at run time, which means you can dynamically control configuration and provisioning.

Profiles make it possible to control a group of nodes (or all nodes) in a single operation. For example, you could set global configuration properties that affect all nodes, or properties that affect only a group of nodes (for example, affecting only message brokers, or affecting only web servers).

Each container registers details of its machine, host name and connection URLs (for example, its JMX URL) with the ZooKeeper runtime registry. Consequently, it is relatively easy to discover a node's location and its connection details by introspecting the fabric. For example, to perform operations on a remote fabric container from within the fuse console, all that you need to know is the container's name.

In addition, Fabric supports a number of discovery mechanisms for discovering application endpoints and services in the fabric—see Appendix D, Technology-specific Discovery Mechanisms for details.