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Chapter 1. Overview

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

Instance HA automates the evacuation of an instance whenever its host Compute node fails. The evacuation process triggered by Instance HA is similar to what users can do manually, as described in Evacuate Instances. Instance HA works on shared storage and local storage environments, which means that evacuated instances will maintain the same network configuration (static ip, floating ip, and so on) and characteristics inside the new host, even if they are spawned from scratch.

Instance HA is managed by three 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, and runs on one of the Controller nodes

nova-compute-wait

nova-compute-checkevacuate

Restarts Compute services on an instance once it is fully evacuated to a functional Compute host.

This guide focuses on enabling Instance HA on an overcloud through Ansible.

Note

For a brief description of the detection and evacuation process performed by Instance HA, see Appendix A, Automated Evacuation Through Instance HA.