Keeping ESXi hosts and vCenter Servers up-to-date is not only an essential best practice, but it's strongly recommended to ensure the correct functionality of the virtual platform and protection from bugs. Several methods are available for patching ESXi hosts via the use of  VUM (this will be discussed later in this chapter) to update all hosts automatically. Alternatively, if no vCenter Servers are present in the network, the command line of the ESXi server can be used as well. Also, the vCSA can be patched in different ways, all of which will be analyzed later on.

There are two different upgrade types:

• Minor updates: From one build to a higher one, but still within the same major version. For example, from ESXi 6.5 U1 (build 5969303) to ESXi 6.5 U2 GA (build 8294253).
• Major updates: From one major version to a higher major version. For example, from ESXi 6.5 U2 GA (build 8294253) to ESXi 6.7 GA (build 8169922).

If you are performing a minor update of your ESXi servers, it is not necessary to upgrade your vCenter Server. If you are performing a major update, vCSA must be updated before you update your ESXi servers, otherwise it will not be able to manage the newer hosts.