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Changing the vCPUs or memory for an instance

asked 2013-12-22 21:37:51 -0500

Stephen C gravatar image

My specific context is NeCTAR, but I'm asking here more generally about the capabilities of OpenStack.

I'm dealing with a situation where I have to request a license key for a 3rd party product to run on NeCTAR / OpenStack. The license key is tied to the MAC address of the "machine" it runs on.

Unfortunately, it appears that OpenStack does not provide a simple way to assign a specific MAC address to a virtual instance as you are configuring / instantiating it. (Certainly, it is not possible via the Grizzly Dashboard ... though perhaps there is another way.) And if I terminate the existing and create a new instance, the new one will have a different MAC address and IP address ... and I'll need to ask for a new license key.

I have been told of a partial workaround that involves "rebuilding" an instance from a fresh image. When you do this, the MAC address and IP address for the instance remain the same. Unfortunately, so does the "flavour"; e.g. the #vCPUs and the memory size ... apparently.

What I'm asking is whether there is a way to change an instance's memory size and # vCPUs that doesn't also entail changing the instance's MAC or IP addresses. (Changing the MAC address has the problem of license key. Changing the IP address has other problems.)

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answered 2013-12-23 00:51:45 -0500

jtopjian gravatar image

As far as I know, the best way to handle this is to make note of the MAC, then edit the new instance's configuration on the hypervisor (for example: edit /etc/libvirt/qemu/instance-00000002.xml if KVM) and change the new MAC to the original MAC. I've had to do this in the past for the same reason that you're running into.

The other option I can think of is to create a dummy/software NIC inside the instance's operating system and bridge it to the real NIC. This way you should be able to control the MAC on the dummy NIC and if the software accepts that MAC, then you're now unconstrained by OpenStack. I've never tried this, though.

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Asked: 2013-12-22 21:37:51 -0500

Seen: 776 times

Last updated: Dec 23 '13