On Sat, Jul 23, 2011 at 2:40 AM, Mark McLoughlin markmc@redhat.com wrote:
Hi Andrew,
On Fri, 2011-07-22 at 08:19 +1000, Andrew Beekhof wrote:
Are there any conditions under which /etc/machine-id would get regenerated? If so that would rule it out.
These were my initial thoughts:
Immutable: /etc/machine-id (systemd)
On reflection, I think Filesystem might be a better label for this scope.
Hardware: ? Something on top of the smbios API Reboot: ? /var/lib/dbus/machine-id (dbus) Agent: In memory using the libuuid API User: /etc/custom-machine-id
Okay, AIUI it (and I've take a quick look to confirm), both /etc/machine-id and /var/lib/dbus/machine-id are basically equivalent concepts
They are both a UUID that should be generated when the machine is installed or booted for the first time and not change thereafter.
Ok, so it looks like the dbus uuid is of no use for the reboot scope and needs to be substituted with something else. I suspected as much - which is why I put a '?' in front of it.
I suspect the simplest path forward is to put something generated by libuuid into /var/run/matahari-reboot-id
Looking at the code, I think dbus and systemd make an effort to have these UUIDs be identical, but I'm not 100% sure. Hmm, I just checked an F-16 machine and the two UUIDs are different.
The reference you've probably seen in the dbus docs to the UUID changing on reboot only applies to stateless systems - the UUID is stored on a part of the filesystem which may not persist across reboots. That could equally apply to /etc/machine-id too.
Based on your summary at the end I think we're arguing the same thing, but clearly in order to have a persistent UUID you need to have access to persistent storage. If we don't have that, we can't use that kind of UUID. End of story.
If people don't want to pre-configure something, then a hardware UUID (either read from the hardware or generated based on what is installed) is really the only option.
I'm quite happy to have Matahari's 'Hardware' UUID use smbios if available* and do something with MAC addresses (and/or some other hardware identifier) if smbios is empty/unavailable.
* From what I can tell, RHEV, VMware and EC2 all support smbios... anyone who doesn't?
In VM disk images, both of these UUIDs should be deleted so that they are generated when a new VM is booted from the image. Similar to what is done for host SSH keys.
On the RHEV-M side, there's a UUID in SMBIOS that has nothing to do with dbus or systemd. This UUID corresponds to the instance ID you'd see in the deltacloud API.
When you launch a deployable, you'll get the list of deltacloud instance IDs back. I'm guessing you want Matahari to reliably report this UUID back as a "system hardware UUID"?
I did list smbios as an option for the Hardware UUID but not because it has anything to do with deployables. Matahari is not a cloud-specific project.
In that case, the answer when running under RHEV-M is to read the UUID from SMBIOS.
Under EC2, you get the ID from:
http://169.254.169.254/latest/meta-data/instance-id
and this isn't a UUID at all. I'm not sure about other clouds.
As long as its unique, Matahari doesn't care which uuid format (if any) its in.
Now, config server seems to have its notion of a machine UUID. This is passed to the instance at launch time and the audrey startup script has logic to find it. The idea is that this is supplied to config server by whatever is launching the instance. I'm not sure why this wouldn't also be the deltacloud ID.
Summary:
- For the HA stuff, I think you need Matahari to be able to reliably report the deltacloud instance ID a "system hardware ID" or similar
You basically mean something persistent right? Matahari isn't going to have a notion of a deltacloud ID, but if deltacloud arranges for its ID to be available (either via something like smbios or but pre-populating a known file on disk), then Matahari will happily return it.
- That's unrelated to the systemd and dbus IDs, but these IDs should be unique to each machine too.
- You should be able to determine the deltacloud instance ID from inside each VM.
- This deltacloud instance ID should be what Audrey is using when contacting config server.
- Audrey and Matahari should have the same logic for figuring this ID out.
Cheers, Mark.