When using LoadMaster in High Availability on AWS, HA operates in much the same way as it does on non-cloud platforms, but with some key differences due to how HA interacts with the AWS Elastic IP feature:

  • LoadMaster HA for AWS involves two LoadMasters that synchronize. Changes made to the active LoadMaster are replicated to the standby LoadMaster.
  • When synchronizing the GEO settings from active to standby, any Fully Qualified Domain Name (FQDN) or cluster IP addresses that match the active’s IP address are replaced with the standby’s IP address. Likewise, when synchronizing from standby to active, the standby’s IP address is replaced with the active’s IP address.
  • All user-defined settings are synchronized, with the exception of the following:
    • Default gateway (both IPv4 and IPv6)
    • IP addresses and netmasks
    • Hostname
    • Name server
    • Domain
    • Admin default gateway
    • Administrative certificate settings
    • Network interface settings: Link Status (Speed and Duplex), MTU and additional addresses
    • Virtual LAN (VLAN) configuration
    • Virtual Extensible LAN (VXLAN) configuration
    • Additional routes
  • The cloud HA LoadMaster does not have a “force update” option.
  • Both devices are capable of responding to Network Load Balancer health check requests.
    • The LoadMaster that is currently handling client traffic will respond with the status code 200 OK to the AWS health check - meaning that it is healthy. Meanwhile, the standby LoadMaster will respond with the status code 503 -- meaning that it is unhealthy. In this way, all client requests are redirected by the Network Load Balancer to the healthy LoadMaster.
    • The “standby” LoadMaster (the LoadMaster which is not handling traffic) polls the “active” LoadMaster to check the availability of the service. If the probe is successful, it remains in “standby” mode, otherwise it takes over as the “active” - answering 200 OK to the AWS health check becoming capable to handle traffic.
Note: If the active unit fails, connections are directed to the standby unit. The active unit never assumes the standby role and the standby never becomes active. When the active unit becomes available again after a failure, connections are automatically directed to the active unit again. The active unit can be active or standby. The standby unit can be active or standby.You can set the Switch to Preferred Server option to No Preferred Host which allows the standby unit to maintain the active state when the active unit comes back online.For HA to work, the two LoadMasters must have different values set for the AWS HA Mode.We recommend always using NIC0 for HA checks on AWS.

A complete description of non-cloud LoadMaster HA can be found in the High Availability (HA), Feature Description document.