Most VMware appliances (vCenter Appliance, VMware Support Appliance, vRealize Orchestrator) have the so called VAMI: the VMware Appliance Management Interface, generally served via https on port 5480. VAMI offers a variety of functions, including "check updates" and "install updates". Some appliances offer to check/install updates from a connected CD iso, but the default is always to check online. How does that work?VMware uses a dedicated website to serve the updates: vapp-updates.vmware.com. Each appliance is configured with a repository URL: https://vapp-updates.vmware.com/vai-catalog/valm/vmw/PRODUCT-ID/VERSION-ID . The PRODUCT-ID is a hexadecimal code specific for the product. vRealize Orchestrator uses 00642c69-abe2-4b0c-a9e3-77a6e54bffd9, VMware Support Appliance uses 92f44311-2508-49c0-b41d-e5383282b153, vCenter Server Appliance uses 647ee3fc-e6c6-4b06-9dc2-f295d12d135c. The VERSION-ID contains the current appliance version and appends ".latest": 6.0.0.20000.latest, 6.0.4.0.latest, 6.0.0.0.latest.
The appliance will check for updates by retrieving the repository URL /manifest/manifest-latest.xml . This xml contains the latest available version in fullVersion and version (fullVersion includes the build number), pre- and post-install scripts, EULA, and a list of updated rpm packages. Each entry has a that can be appended to the repository URL and downloaded. The update procedure downloads manifest and rpms, verifies checksums on downloaded rpms, executes the preInstallScript, runs rpm -U on the downloaded rpm packages, executes the postInstallScript, displays the exit code and prompts for reboot.
With this information, you can setup your own local repository (for cases where internet access is impossible from the virtual appliances), or you can even execute the procedure manually. Be aware that manual update would be unsupported. Using a different repository is supported by a subset of VMware appliances (e.g. VCSA, VRO) but not all (VMware Support Appliance).
