To ensure that you always have access to the BIG-IP® devices under BIG-IQ® system management, install two BIG-IQ systems in a high availability (HA) configuration. Configuring for high availability is optional.
With BIG-IQ high availability, the BIG-IQ system periodically replicates the entire BIG-IQ system state from the primary peer to the secondary to keep the two systems synchronized. This synchronization allows the secondary peer to be promoted to be the primary and take over management of the BIG-IP devices if the primary system is not fully functional. There is no automatic fail over from the primary to the secondary.
How often the primary and secondary are synchronized is configurable. In the BIG-IQ HA data replication model, this synchronization interval determines how many minutes is acceptable for the secondary peer to be out-of-date with the primary. By default, the secondary is synchronized with the primary every 10 minutes.
When you initially set up an HA pair, the systems are synchronized and you can see the configuration of what was on the primary updated on the secondary. Subsequently, when you synchronize the systems, you will not see the configuration change since the changes will be copied to the secondary system, but will not be used to update the configuration at that time. If you want to have the configuration updated on the secondary BIG-IQ system, log in to the secondary system and use the Restart with Last Update from Primary option.
If the primary BIG-IQ system in an HA cluster fails, then you need to log in to the secondary BIG-IQ system and promote it to being the primary BIG-IQ system.
If you restore a BIG-IQ system configuration using a compressed user configuration set (UCS) file, there are additional tasks you need to perform if that system is in an HA cluster. After restoring the BIG-IQ system configuration, you need to split the HA cluster that system is part of and then recreate the HA cluster.
Terminology is crucial in understanding the status of the high availability (HA) relationship. The following list defines some important terms used in HA configurations.
The secondary system applies the last set of configuration changes it received from the primary system, and then restarts.