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Chapter 18.
233
System Reliability and High Availability
18.1. HA for Management Server
The CloudPlatform Management Server should be deployed in a multi-node configuration such that
it is not susceptible to individual server failures. The Management Server itself (as distinct from the
MySQL database) is stateless and may be placed behind a load balancer.
Normal operation of Hosts is not impacted by an outage of all Management Serves. All guest VMs will
continue to work.
When the Management Server is down, no new VMs can be created, and the end user and admin UI,
API, dynamic load distribution, and HA will cease to work.
18.2. HA-Enabled Virtual Machines
The user can specify a virtual machine as HA-enabled. By default, all virtual router VMs and Elastic
Load Balancing VMs are automatically configured as HA-enabled. When an HA-enabled VM crashes,
CloudPlatform detects the crash and restarts the VM automatically within the same Availability Zone.
HA is never performed across different Availability Zones. CloudPlatform has a conservative policy
towards restarting VMs and ensures that there will never be two instances of the same VM running at
the same time. The Management Server attempts to start the VM on another Host in the same cluster.
HA features work with iSCSI or NFS primary storage. HA with local storage is not supported.
18.3. Dedicated HA Hosts
One or more hosts can be designated for use only by HA-enabled VMs that are restarting due to
a host failure. Setting up a pool of such dedicated HA hosts as the recovery destination for all HA-
enabled VMs is useful to:
• Make it easier to determine which VMs have been restarted as part of the CloudPlatform high-
availability function. If a VM is running on a dedicated HA host, then it must be an HA-enabled
VM whose original host failed. (With one exception: It is possible for an administrator to manually
migrate any VM to a dedicated HA host.).
• Keep HA-enabled VMs from restarting on hosts which may be reserved for other purposes.
The dedicated HA option is set through a special host tag when the host is created. To allow the
administrator to dedicate hosts to only HA-enabled VMs, set the global configuration variable ha.tag
to the desired tag (for example, "ha_host"), and restart the Management Server. Enter the value in the
Host Tags field when adding the host(s) that you want to dedicate to HA-enabled VMs.
Note
If you set ha.tag, be sure to actually use that tag on at least one host in your cloud. If the tag
specified in ha.tag is not set for any host in the cloud, the HA-enabled VMs will fail to restart after
a crash.