[Maas-devel] MAAS managed DNS

[Robert Collins]

On Thu, Jul 19, 2012 at 4:53 PM, Julian Edwards
<julian.edwards at canonical.com> wrote:
>
> Howdy
>
> This isn't an approach that was considered when designing the DNS stuff
> (forgive me if it was, I've been on parental leave for 2.5 weeks).  However,
> bulk pre-allocation does solve a couple of problems and I like it a lot.
>
> The main problem is DNS Latency.  When updating the DNS based on randomly
> DHCP-assigned IPs to hosts, there's a latency introduced with the celerybeat
> polling approach that we had in mind.  If the zone files remain relatively
> static (they'd be written only when the IP range for the nodegroup changes),
> this simply ceases to be a problem at all.
>
> I don't think this will be difficult to do - it just means we change the event
> that triggers writing out the zone files (to when NodeGroup is added/updated).
> Raphaël, we *do* still need to consider classless masks though and use
> RFC2317.

Or use stock standard zones, and just replicate the full set to all
the DNS servers, which will give you better response times and natural
redundancy of service. I recommend this ;).

> A second problem is one that came up just now on IRC when I was discussing
> this with Rob: we must never allow the IP address of an allocated node to
> change, because it will break things like Juju which assume it won't change.
> When someone reboots an allocated node in a busy pool, it's highly likely it
> will get a new IP when coming up again.
>
> To solve this I just discussed a couple of options with jtv:
>  1. Write out dhcp configs for static mappings of MAC to IP.
>  2. Use a very long lease time.
>
> We preferred the second option because the first means that we either have to
> manually allocate IP addresses (thus defeating one of the points of a DHCP
> server really), or we have to detect what the IP address was via the leases
> file and write that mapping back to a static config, which introduces a
> problematic latency.
>
> If we use a long lease time, the only real problem is removing it when
> decommissioning a node.  We should be able to do this easily with the omshell
> utility which uses the OMAPI facility that ISC DHCP has.

What about assigning the IP during commissioning, so that you don't
have to change the nodes address at any point - when its enrolling it
gets dynamic address, when you enroll it into the system you assign a
static address.

FWIW, I've had much better results in previous (special case but
similar bits) projects using static allocation: it avoids all the
things that *can* go wrong with long leases (such as nodes choosing to
relinquish the address and then getting a different one). I don't see
that it would add any latency to the provisioning process either,
though IMBW.

-Rob