
To improve Dispatcher availability, the Dispatcher high availability
functions as follows:
- 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.
- 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.
- 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.
- Synchronization of the Dispatcher information
- 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.
- 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.