Comment 3 for bug 1370384

@boden
>> is this for AWS parity?
Exactly!

If we claim AWS compatibility, typical AWS scenarios should work fine. This resizing scenario is declared by AWS.
As i understand, the compatibility means, that an end user EC2 script with this scenario should do it's work properly as it is against OpenStack. But now it's not the case.

Moreover there is no other way to resize a root volume by EC2 API.

As you mentioned above we can allow to detach root disk when an instance is stopped. I guess that current prohibition is not the result of deep digging, but the result of easy fixing of https://bugs.launchpad.net/nova/+bug/1279300 (detach boot device volume without warning).

Also for attaching a root device back - as i see, the problem is inspired by usage of block_device.instance_block_mapping to get all current device names. But block_device.instance_block_mapping returns root device even though it isn't attached (and this is used in other case when it's called).

Thus Nova doesn't contain explicit restrictions to reattach a root device. Nova architecture allows this, but certain minor parts of code prevent it. So i reopen the bug. I hope it can be resolved.