In high availability mode, two vCenter Single Sign-On nodes work with the same database, data, and user stores to ensure that vCenter Single Sign-On is not a single point of failure.
This procedure upgrades an existing vCenter Server that was installed with a high availability vCenter Single Sign-On deployment.
You can upgrade vCenter Single Sign-On in a high availability installation without taking all vCenter Single Sign-On nodes offline at the same time. While the first Single Sign-On node is being upgraded, the load balancer will redirect all requests to the second node. After the first node is successfully upgraded, you can upgrade the second node.
vCenter Server can continue running while you upgrade vCenter Single Sign-On. Logged in users can continue accessing vCenter Server and related solutions that are connected to vCenter Single Sign-On during the upgrade. However, vCenter Server, the vSphere Web Client, and vCenter Inventory Service cannot be started while the first Single Sign-On node is offline.
Note: vCenter Server 5.5 supports connection between vCenter Server and vCenter Server components by IP address only if the IP address is IPv4-compliant. To connect to a vCenter Server system in an IPv6 environment, you must use the fully qualified domain name (FQDN) or host name of the vCenter Server. The best practice is to use the FQDN, which works in all cases, instead of the IP address, which can change if assigned by DHCP.