Legacy active/standby high availability (HA) is available for NSX Advanced Load Balancer Service Engine (SE) redundancy. Legacy active/standby is useful for migrating from hardware appliance-based solutions.
NSX Advanced Load Balancer also provides elastic HA, including active/active and N+M modes. In legacy HA mode, only two NSX Advanced Load Balancer SEs are configured. By default, active virtual services are compacted onto one SE as illustrated in the image below. In this mode, one SE carries all the traffic for a virtual service placed on it and is thus the active SE for that virtual service. The other SE in the pair is the standby for that virtual service that does not carry traffic for it while the other SE is healthy.
Upon failure of an SE, the surviving SE takes over traffic for all virtual services that were previously active on the failed SE, by continuing to handle traffic for virtual services that are already assigned to it. As part of the takeover process, the survivor also takes ownership of all floating IP addresses such as VIPs, SNAT-IP and so on. The Compacted and Distributed options determine whether all active virtual service placements are concentrated onto one SE in a healthy pair or not.
NSX Advanced Load Balancer supports rolling upgrades by the NSX Advanced Load Balancer Controller of SEs in a legacy HA configuration. Virtual services running on a legacy HA SE group are not disrupted during a rolling upgrade. The below image depicts Legacy HA active/standby, displaying Compacted and Distributed load options. The Standby virtual services are shown in light grey.
By default, health checks are sent by both NSX Advanced Load Balancer SEs to back-end servers and Gateway health checking is supported for both NSX Advanced Load Balancer SEs. The user can prefer to do any of the following tasks listed below:
You can disable health monitoring by an SE for virtual services for which it is standing by.
You can enable health checks for each NSX Advanced Load Balancer SE’s next hop gateways.
Floating IP Address
You can assign one or more floating IP addresses to a SE group configured for legacy HA. The floating IP address is applicable when the SE interfaces are not in the same subnet as the VIP or source NAT (SNAT) IP addresses that uses the SE group. One floating interface IP is required per each attached subnet per SE group while configuring in the Legacy HA mode.
Disabling a Legacy-Mode SE
A combination of factors cause the disabling of a legacy-mode SE, that is different from SEs running in either active/active or N+M mode. For more information, refer to Disable SE article.