Yes, it's technically possible, as long as the underlying hardware is compatible. For example, you can't put a server using AMD processors into a pool with Intel processors.
The server being moved into the existing pool will lose its local storage and all VMs stored there, so you will need to migrate those VMs to the main pool before the server is merged. Afterwards, you can move them back if desired.
You're running out of memory. Allocate more memory to the VM. I believe the current build requirement is 3GB.
You need a space between the URL and the user name.
Updated Dell R620 / XCP-ng 8.1. Rebooting all VMs now, but they appear to be coming up just fine.
@hvilches said in XCP-ng Center 20.03.00 released:
is-a-template ( RW): true
Looks like this is the culprit...
@flipsidecreations There's a new Netdata plugin, which appears to only be available in XOA Premium edition. It doesn't appear that you will be able to enable the new Advanced Live Telemetry using the versions you are currently running.
@olivierlambert The "quick deploy" via web worked correctly this time 
@stormi Thanks. I expanded the disk and now the build completed. I'll report back if I come up with any meaningful results.
@delaf I ran into the same thing recently. See solution below --
@nicolai-comar said in Error when taking a snapshot in XO:
xo-server 5.12.1 and xo-web 5.12.0
Those are really out-of-date. Please update to the latest available versions and try again.
@cg Did you try xe vm-cd-eject --multiple to eject all CDs?
@cg You could try checking the logs (both XOA and XCP-ng) to see if that yields any further details. Have you tried starting the VM from the CLI?
A few questions --
What are the hardware specs for the host?
Have you verified that virtualization support is enabled in the BIOS?
Is XOA running as a VM on this same host?
P.S. A single host is technically still running in a pool 
@capeschools I think he means in the BIOS
@capeschools In that case, @olivierlambert's advice is best --
migrate VMs from XS to XCP-ng, no need for conversion
@olivierlambert I didn't mean to imply that Vates ever made such a claim. I was simply responding to the issue in the OP, which is where the removal of support for Centos 7 was first mentioned.
P.S. Happy New Year! 
What process are you using to perform the import?
Are you aware that you can perform an in-place upgrade from xenserver to xcp-ng?
@bberndt I doubt that support has been removed for centos 7. It's more likely that a required 3rd party library needs to be updated or built from source.
Did you encounter any issues during the actual build process?
XOA is the pre-built appliance from Vates. XO is the open source project, and you can follow these official instructions to build it from source.
Note 1: You don't install it directly in Dom0. Instead you create a Linux VM (Debian, Ubuntu, or whatever) and install it there.
Note 2: If you look around, there are multiple user created and maintained scripts that allow you to automate the instructions from the above link.