Chapter 1. Overview

This guide describes how to implement Instance High Availability (Instance HA). Instance HA allows Red Hat OpenStack Platform to automatically evacuate and re-spawn instances on a different Compute node when their host Compute node fails.

The evacuation process that is triggered by Instance HA is similar to what users can do manually, as described in Evacuate Instances.

Instance HA works on shared storage or local storage environments, which means that evacuated instances maintain the same network configuration (static IP, floating IP, and so on) and the same characteristics inside the new host, even if they are spawned from scratch.

Instance HA is managed by the following resource agents:

Agent nameName inside clusterRole

fence_compute

fence-nova

Marks a Compute node for evacuation when the node becomes unavailable.

NovaEvacuate

nova-evacuate

Evacuates instances from failed nodes. This agent runs on one of the Controller nodes.

Dummy

compute-unfence-trigger

Releases a fenced node and enables the node to run instances again.

This guide describe how to use the Ansible automation framework to enable Instance HA. For more information about Ansible, see Ansible Documentation.

Note

For a high-level description of how Instance HA detects and evacuates instances from failed hosts, see Chapter 2, How Instance HA Works.