The vSphere Web Client made it's debut some time ago, before W3C released their HTML5 recommendation and browser support for it became ubiquitous. Given the vast range of functionality manageable in vSphere, having a console based on Adobe Flash made sense as a means to deprecate the older C# client.

Fast-forward to 2017 and Adobe announced their intention to sunset Flash. Announcements from the major players in the browser market followed, including:

Why does any of this matter? Well, full HTML5 functionality in the vSphere Client starts at version 6.7U1 but vSphere 6.5 is not End-of-Life until November 2021. So anyone still running vSphere 6.5 could find themselves in a situation where certain vSphere features cannot be configured or managed because their browsers no longer allow them to run Adobe Flash.

Following some questions from customers about this, I put together a timeline to illustrate the situation to the vSphere product managers.

Adobe Flash / vSphere Web Client support timeline

Last night the vSphere team published their recommendation to customers still on vSphere 6.5 - "vSphere Web Client Support beyond Adobe Flash EOL". The TLDR version is that vCenter should be upgraded to version 6.7 Update 3. This can be done even if your ESXi hosts cannot be upgraded from 6.5 for some reason.

Finally, if you keep vCenter at 6.5, the following documentation page describes the functionality available in the vSphere Client (i.e. HTML5, not Flash): https://docs.vmware.com/en/VMware-vSphere/6.5/rn/vsphere-client-65-html5-functionality-support.html