Needed: Node and Engine cooperation

[Fabian Deutsch]

Hey,

with the extraction of the oVirt Engine / VDSM specific bits from Node
in it's 3.0 release, oVirt Node became unaware of when it is being
managed.
Pre-3.0 Node (it's TUI) had specific knowledge about what configuration
files existed when it was registered to Engine. This is not the case in
Node 3.0 anymore. And this leads to problems. E.g. a user removing
Engines network layout.

A new way is needed to pass informations between the management instance
and Node's core. This informations are needed e.g. to prevent the user
from accidentally destroying Engines network layout on a Node.

I've opened a bug [0] to suggest a way of sharing this kind of
informations.

The idea is that Node and the management instance - Engine - share a set
of common configuration keys in /etc/default/ovirt to pass the relevant
bit's to Node.
For now I thought about this three keys:


OVIRT_MANAGED_BY=<vendor>
This key is used to (a) signal the Node is being managed and (b)
signaling who is managing this node.

OVIRT_MANAGED_IFNAMES=<ifname>[,<ifname>,...]
This key is used to specify a number (comma separated list) of ifnames
which are managed and for which the TUI shall display some information
(IP, ...).
This can also be used by the TUI to decide to not offer NIC
configuration to the user.

OVIRT_MANAGED_LOCKED_PAGES=<pagename>[,<pagename>,...]
(Future) A list of pages which shall be locked e.g. because the
management instance is configuring the aspect (e.g. networking or
logging).


The third one (OVIRT_MANAGED_LOCKED_PAGES) needs a tighter integration
and might be relevant in the future, but the first two should really be
implemented quickly for the reasons given above.

It is quit elate in the development process but probably worth to think
about getting this into 3.3.1, to prevent all sorts of (accidentally)
user-driven collisions between Node and Engine.

Thoughts?

Greetings
fabian

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[0] https://bugzilla.redhat.com/show_bug.cgi?id=1021647