When you upgrade vCenter Server, you must understand and follow the best practices process for a successful upgrade.
To ensure that each upgrade is successful, follow these best practices:
Make sure that you understand the vCenter Server upgrade process, the effect of that process on your existing deployment, and the preparation required for the upgrade.
If your vSphere system includes VMware solutions or plug-ins, make sure they are compatible with the vCenter Server version that you are upgrading to. See the VMware Product Interoperability Matrix at http://www.vmware.com/resources/compatibility/sim/interop_matrix.php.
Read all the subtopics in Preparing for the Upgrade to vCenter Server.
Read the VMware vSphere Release Notes for known installation issues.
If your vSphere installation is in a VMware View environment, see Upgrading vSphere Components Separately in a Horizon View Environment.
Prepare your system for the upgrade.
Make sure your system meets requirements for the vCenter Server version that you are upgrading to. See System Requirements and the VMware Product Interoperability Matrix at http://www.vmware.com/resources/compatibility/sim/interop_matrix.php.
Verify that your existing database is supported for the vCenter Server version that you are upgrading to. See the VMware Product Interoperability Matrix at http://www.vmware.com/resources/compatibility/sim/interop_matrix.php.
Make sure that your vCenter Server database is prepared and permissions are correctly set. See the information about preparing vCenter Server databases in the vSphere Installation and Setup documentation.
Review the prerequisites for the upgrade. See Prerequisites for the vCenter Server Upgrade.
Back up your vCenter Server databases and SSL certificates
Make a full backup of the vCenter Server database and the vCenter Inventory Service database. For the vCenter Server database, see the vendor documentation for your vCenter Server database type. For the Inventory Service database, see the topics "Back Up the Inventory Service Database on Windows" and "Back Up the Inventory Service Database on Linux" in the vSphere Installation and Setup documentation.
Back up the SSL certificates that are on the vCenter Server system before you upgrade to vCenter Server 5.5. The default location of the SSL certificates is %allusersprofile%\VMware\VMware VirtualCenter.
Stop the VMware VirtualCenter Server service.
Run the vCenter Host Agent Pre-Upgrade Checker, and resolve any issues. See Run the vCenter Host Agent Pre-Upgrade Checker.
Make sure that no processes are running that conflict with the ports that vCenter Server uses. See Required Ports for vCenter Server.
Upgrade vCenter Server and required components.
See the appropriate procedure for your existing vCenter Server deployment:
Configure new vSphere 5.5 licenses.
Review the topics in After You Upgrade vCenter Server for postupgrade requirements and options.