recently put vSphere 5.5 Update to 7.0，Many articles have been published before，This is a sorting，This will be a bit clearer for the entire upgrade process，The entire upgrade procedure is as follows：
1. vCSA 5.5 U3k -> vCSA 6.0 U3i。
2. ESXi 5.5 U3b -> ESXi 6.0 U2。
3. vCSA 6.0 U3i -> vCSA 6.5 U3f。
4. ESXi 6.0 U3f -> ESXi 6.5 U2。
5. vCSA 6.5 -> vCSA 7.0 U1。
6. ESXi 6.5 U2 -> ESXi 6.5 U3。
7. ESXi 6.5 U3 -> ESXi 7.0 U1。
Upgrade order and version selection above，It is planned with reference to several VMware KBs，For related information, please refer to the "reference link" at the bottom of this article。Also if during the upgrade，If the existing ESXi or vCenter is broken due to driver conflicts and other factors, you plan to reinstall，You can refer to the following two articles：
◎ When upgrading ESXi，The difference between Upgrade and Install。
◎ Install vCenter Server Appliance 7.0。
In the process of upgrading，As spanning three major versions，If there is a requirement for upgrading and upgrading of VMware Licence Key，Please refer to the following KB。
◎ How to Upgrade or Downgrade License Keys in Customer Connect with troubleshooting steps (81665)
After the upgrade is complete，It is recommended to upgrade VMware Tools，Let vSphere's various monitoring and management functions of the VM continue to operate normally；And the hardware version of the VM，You don’t have to upgrade，Only need to upgrade when using new hardware compatibility related functions。If you want to raise both，It is recommended to upgrade VMware Tools first，Upgrade the hardware version again。
【參考連結】
- Product Interoperability Matrix
- VMware vCenter Server 7.0 Update 2 Release Notes
- vCenter Server Upgrade Compatibility
- vSphere Back-in-time release upgrade restriction (67077)
- Upgrade a vCenter Server Appliance 5.5 or 6.0 with an Embedded vCenter Single Sign-On or Platform Services Controller by Using the GUI
- Using HPE Custom ESXi Images to Install ESXi on HPE ProLiant Servers | HPE
- Back up, install, migrate and set up to follow the steps to upgrade to vSphere 7 painlessly(Next) | Webmaster
- Upgrade the ESXi host and its virtual machines
