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Chapter 2. Environment Requirements and Assumptions

In order to enable Instance HA, your Red Hat OpenStack Platform overcloud must meet the following requirements:

  • The environment was deployed using Red Hat OpenStack Platform director. See Director Installation and Usage for details.
  • Fencing has already manually been enabled on the control plane.

  • The following packages are installed on all nodes:

    • fence-agents-4.0.11-66.el7_4.3 (or greater)
    • pacemaker-1.1.16-12.el7.x86_64 (or greater)
    • resource-agents-3.9.5-105.el7.x86_64 (or greater)
  • The environment can tolerate a full outage of both Compute and Control planes.
  • Shared storage is enabled within the environment for ephemeral and block storage. See Section 2.1, “Exceptions for Shared Storage” for related information.

  • The Message Broker (AMQP) recognizes each Compute node’s hostname as valid. To check the hostname of a Compute node: 

    heat-admin@compute-n $ sudo crudini --get /etc/nova/nova.conf DEFAULT host
    Copy to Clipboard Toggle word wrap

  • Each Compute node should be able to reach the endpoint set in $OS_AUTH_URL. In addition, this environment variable must be set to either:

    • The overcloud’s authentication service (which requires access to the external network), or
    • The internal authentication URL.
Warning

When Instance HA is enabled, overcloud upgrade or scale-up operations are not possible. Any attempts to do so will fail. This includes both minor and major upgrades.

Before upgrading or scaling your overcloud, disable Instance HA first. For instructions, see Chapter 5, Rollback.

2.1. Exceptions for Shared Storage
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Typically, enabling Instance HA requires shared storage. If you attempt to use the no-shared-storage option, you are likely to receive an InvalidSharedStorage error during evacuation, and instances will not power up on the other node. However, if all your instances are configured to boot up from a Block Storage (cinder) volume, then you will not need shared storage to store the disk image of instances; you will be able to evacuate all instances using the no-shared-storage option.

During evacuation, if your instances are configured to boot from a Block Storage volume, any evacuated instances can be expected to boot up from the same volume, but on another Compute node. As a result, the evacuated instances can immediately restart their jobs, as the OS image and application data are kept on the Block Storage volume.

Note

The ansible-based deployment procedure in this guide supports installation with no-shared-storage option.

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