VMware vSphere upgrade process is usually an easy process to execute, due to the vSphere Update Manager simplicity, but it requires a careful planning and attention on the different compatibility and interoperability matrix.
An important note is about the different build versions (or the Update releases) of the different components.
People probably remembers that was not possible upgrade from vSphere 6.5 to vSphere 6.7 if you have first upgraded the 6.5 release to the Update 2 patch. This issue was resolved with the vSphere 6.7 Update 1 release.
This kind of issue potentialially appears each time a new product’s patch is released for an old version branch and the release data is more recent than the release date of the main branch patches.
For example let’s consider the upgrade paths for VMware vSphere 6.7 release.
Note that the Upgrade Path web site will really help you in all this pre-check activities.
First to all we have to upgrade the vCenter Server, so let’s check the upgrade compatibility matrix for the different versions (remember that vCenter 6.7 can manage and upgrade only 6.x versions):
As you can notice it’s not possible upgrade from 6.5U2 to 6.7 (but it’s possible upgrade to 6.7U1) because “back in time” upgrade not supported (vSphere 6.7.0 released before vSphere 6.5 U2). Note that for the same reason is neither possible upgrade from 6.0U3 to 6.5 (but it possible to 6.5U1 or later).
But there are several notes also for the other versions matrix. For example you have to take care if you try to upgrade the vCenter 6.5 with patches post 6.5 U2, dated November 2018 or after: the upgrade to 6.7 U1 are unsupported as it is considered back-in time.
Yes… isn’t nice at all… If you keep your system updated you can have issues with the upgrade path.
Now let’s consider the ESXi upgrade path:
In this case you have less limitations: of course you can’t upgrade from ESXi 6.5U2 to ESX 6.7 (but it’s possible to 6.7U1)… but you don’t have big issues if you have an updates ESXi post 6.5U2.
Still you have to check the hardware compatibility and different driver and firmware versions, but you have less constraints.
And for Active Directory environments, remember that only
VMware vSphere 6.7U1 supports Active Directory 2016