Adaptive lease time patch

[Christof Chen]

> That's worse.
>
> lease-time comes to us as 5 for whatever reason (bogus arbitrary number).
> min-lease-time is 10.
> The lease expires in 20.
> min-lease-time = 20;
> lease-time exits as 5, and gets assigned to 20.
>
> In this case tho it should exit as the configured min-lease-time, 10.

Wasn't it the idea to gracefully allow a client to use up its previously
assigned lease time (here 20), before shorting the lease? This is the same
as if the client has not renewed at all...

> I suspect the fixed limit will be both easier to implement and
> equivalent (X% of a pool of Y leases is always Z), so I would
> probably lean in that direction.

I have many pools with different Y, so a single Z does not really fit. I
implemented the percentage - which, being equivalent :) - works also for
those with constant pool sizes.

> Also, it suddenly strikes me to consider failover.
>
> The question is wether the count of free or backup leases should be
> summed or if each server should only consider its own pool.

Sorry - i have not much experience with failover yet. But the failover
draft states on page 30  that the secondary can allocate a backup ip at
any time. So that would suggest it counts to the number of assignable
(free) leases.

Christof Chen