How high availability works

Example of Load Balancer using high availability

To improve Dispatcher availability, the Dispatcher high availability functions as follows:
  1. Two Dispatchers with connectivity to the same clients, and the same cluster of servers, as well as connectivity between the Dispatchers. Both Dispatchers must run on the same type of operating system and platform.
  2. A “heartbeat” mechanism between the two Dispatchers detects a Dispatcher failure. At least one heartbeat pair must have the NFAs of the pair as the source and destination address. If possible, at least one of the heartbeat pairs should be across a separate subnet than the regular cluster traffic. Keeping the heartbeat traffic distinct will help prevent false takeovers during very heavy network loads and also improve complete recovery times after a failover.
  3. A list of reach targets, addresses that both Dispatcher machines must be able to contact in order to load balance traffic normally. For more information, see Detecting server failures with heartbeats and reach targets.
  4. Synchronization of the Dispatcher information
  5. Logic to elect the active Dispatcher which is in charge of a given cluster of servers, and the standby Dispatcher which continuously gets synchronized for that cluster of servers.
  6. A mechanism to perform IP takeover, when the logic or an operator decides to switch active and standby.

Planning for high availability

When configuring for high availability, consider that the Load Balancer machine is supported with the following limitations or special considerations:
  • If you are using IPv6 protocol on your machine and want to use high availability, you must check to see if protocol 58 is defined to be ICMPv6 in the protocol file.
  • In the high availability configuration, both primary and backup machines must be on the same subnet with identical configuration.
  • The heartbeat pairs (which is the mechanism between the primary and standby Dispatchers to detect Dispatcher failure) must be both IPv4 format or both IPv6 format.
  • In a high availability or a stand-alone environment, you must not alias the cluster address against the network adaptor.
  • The HighAvailChange script can be moved from the install_root/servers/samples directory to the install_root/servers/bin directory to log high availability state changes for the Dispatcher machine, but this script does not need to be changed.
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Last updated: May 14, 2012 02:14 PM EDT
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