The migration assistant can tackle a couple of different vCenter Server configurations:

• vCenter Server 5.5 or 6.0 with an embedded vCenter Single Sign-On instance on Windows
• vCenter Server 5.5 instance on Windows with external SSO
• vCenter server 6.0 instance on Windows with external PSC

Depending on your current configuration, the migration process will change based using an internal or external SSO/PSC and where VUM is installed.

• If VUM is installed on a separate Windows server, other that your Windows vCenter Server instance then you MUST to run the migration assistant on this server FIRST!  The VMware Migration Assistant facilitates the migration of the Update Manager server and database to the vCenter Server Appliance 6.5.
• If embedded SSO/PSC, then you run the Migration Assistant on the source vCenter Server
• If external SSO/PSC, then you run the Migration Assistant on the source SSO/PSC first and then run the Migration Assistant on the source vCenter Server
  • During the migration process, make sure to leave the migration windows open

You run the VMware Migration Assistant on your source vCenter Server, SSO/PSC or VUM it will perform the following tasks:

• Discover the source deployment type.
• Run pre-checks on the source.
• Report errors that must be addressed before starting the migration.
• Provide information for the next steps in the migration process.

Here are my step by step instructions for vCenter Server 5.5 with embedded SSO, no VUM:

1. Download and Mount the vCenter Server Appliance Installer ISO file to the Windows vCenter Server.
2. Start the migration assistant on the source, depending on your environment configuration
   1. Open the installer folder on CD/DVD drive and copy the  “migration-assistant” folder to your source windows server running the vCenter Server
   2. Open the copied folder on local drive and run “VMware-migration-assistant.exe”
      1. This will run the pre-update checklist and prompt if anything needs to be fixed.
      2. Make sure this window stays open during the whole migration process until completion.
3. Launch vCenter server appliance UI installer
   1. Click Migrate
   2. Click Next on Introduction
   3. Accept EULA and click Next
   4. Connect to the source server
      1. Enter Windows server FQDN or IP address
      2. Enter migration assistant port number
         • If you are changing networks and have a firewall in place then pick a port that is open and available.
      3. SSO username
         • administrator@vsphere.local
      4. SSO Password
      5. Click Next
   5. Accept Thumbprint
   6. Appliance deployment target
      1. Enter ESXi or vCenter Server name for targer
      2. HTTPS port
      3. Username
      4. Password
      5. Click Next
   7. Accept Thumbprint
   8. Select Folder to place the new vCSA
   9. Select the compute resource
   10. Target appliance VM
       1. Enter VM name
       2. Enter new root password
   11. Select deployment size
   12. Select datastore
   13. Configure the temporary network identity which is used to copy the data, this will be removed after migration is completed since the target vCSA server will get the network identity of the source vCenter server.
       1. Pick network port group
       2. Enter temp IP address
       3. Enter subnet
       4. Enter GW
       5. Enter DNS servers
       6. Click Next
   14. Verify detailed entered are correct!
   15. Click Finish
   16. Wait for the migration to complete.
       • If the migration fails for any reason your can easily roll back by powering off the target vCSA and then just power on the source vCenter Server and its components.
4. Now for stage two, which copies the data from the source vCenter to new vCSCA.
   1. On Introduction click next
   2. Connect to Source vCenter should complete automatically
   3. Join AD
      • Add username and password for user that can add computer to domain
   4. Select the best migration data options with the following 3 being available. (pretty cool that it provides the size of the migration for each option as well)
      • Just the configuration
      • Configuration, Events and Tasks
      • Configuration, Events, Tasks and Performance metrics
   5. Select if you want to join CEIP and click Next
   6. Review your settings, check the box to verify you have a backup of the vCenter server as well as the database.  Click Next
   7. Click OK on prompt that warns you that the source vCenter Server will be shut down once the network configuration is enabled.
   8. Wait for the data migration to complete.

When successful, your source vCenter Server should now be shut down and brand new shiny vCenter Server appliance should be started in its place. The best part of all you are also upgraded to vCenter Server 6.5! awesome.