iency XenServer can be configured to self monitor for host failures and

Iency xenserver can be configured to self monitor for

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iency, XenServer can be configured to self monitor for host failures and automatically restart impacted virtual machines. 50 | Chapter 4: Design Assumptions Impacting Deployment
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Host Failure Protection Host failure protection, or high availability (HA), uses a combination of network and shared storage heartbeat monitors to determine if a given host within a resource pool is operating. In the event the requisite heartbeat interval isn’t satisfied, the Xen hyper‐ visor watchdog will trip and self-fence the host. This has the direct benefit of ensur‐ ing that crashes and instabilities from within dom0 are also trapped. In the event the pool master is deemed to have failed, one of the surviving hosts—in a discussion with the remaining hosts—will promote a suitable host with enough resources as the new pool master. The pool master then automatically restarts any VMs configured to restart in the event of host failure that were running on the failed server, and VM operations continue with minimal interruption. Host failure protection isn’t designed to detect a VM that crashes or operate with a pool with fewer than three hosts and does require that all protected VMs have no affinities to a specific host and have their disks on shared storage. If host failure pro‐ tection is required for resource pools with fewer than three hosts, an external moni‐ toring and attestation service will be required. The creation of such a service is beyond the scope of this book. Host failure protection also requires that each member within a XenServer pool has multiple paths to both storage, management infrastructure, and other essential net‐ works. In regards to network, this is accomplished via bonded networking; and for iSCSI and Fibre Channel storage, this is accomplished with multipathed storage net‐ works. Even without the host-failure protection enabled, multipathed storage and bonding can help eliminate single points of failure within the storage, management, and infrastructure network. Protection levels VMs in a pool can be protected as “best effort,” “protected,” and “unprotected.” Within each category, a restart priority can be given. Any VM with protected status will automatically be restarted in priority order if there is sufficient remaining capacity to do so. The XenServer pool master continually monitors the status of member servers, and if insufficient capacity existed to restart all protected and best- effort VMs, as new capacity becomes available, the pool master will automatically restart any remaining protected and “best effort” VMs. XenServer HA can be enabled by issuing the command in Example 4-9 , where heartbeat-sr-uuids is the UUID of the shared storage repository on which the heartbeat metadata will be written.
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