[kea-dev] Call for comments about Lease Expiration requirements in Kea

[Tomek Mrugalski]

On 24/06/15 14:27, Marcin Siodelski wrote:
> As a part of the preparation for the Kea 1.0, I would like to ask the
> list participants to review and comment on a document presenting the
> requirements for the "Lease Expiration", which is available here:
> 
> http://kea.isc.org/wiki/LeaseExpirationRequirements
That's a good proposal. Thanks for doing this. I have couple comments:

> G1.MUST execute lease-expiration hook for each reclaimed lease
Do we want to be more specific here that the hook will be called in the
same hook library instance (i.e. the same process/thread) as all the
other hooks? It may be easier for us to create a separate process/thread
that does lease recycling in the background, but it would be much more
difficult for hook lib developers as one of the callouts would be called
in a separate process/thread. On the other hand, if we specify this up
front in the requirements, it may limit the available designs for the
expiration framework. Hmmm, so maybe not saying anything at all here and
keep the text as is would be best?

> C1. MUST provide a configuration switch to disable lease expiration. 
> It MAY be combined with the switch controlling the period between
> two consecutive processing cycles
I would reword it to "... to disable lease expiration during run-time".
I can imagine that, depending on your scenario, one of 3 approaches may
be desired: 1. expire leases once on start-up; 2. expire leases
periodically; 3. expire leases on shutdown. Case 1 is useful when you're
recovering from a blackout or other misfortune. Case 2 is the normal
operation that I expect to be used almost all the time. Case 3 is useful
when you want to squeeze top performance from your server, but still
want to have a clean database/dns afterwards.

I think you should also add two extra requirements. The first one
probably belong to a new administrative section:
A.1 There MUST be a command to manually trigger lease reclaimation.

With the CommandMgr and control socket for statistics implemented,
adding new commands is quite easy.

Another comment is about statistics. Not sure if logging and statistics
should be treated together (they are both used for debugging or general
awareness of what's happening in the system) or separately (logs and
statistics are handled in very different ways). In any case, here's one
entry that should be added:

L4 MUST decrease subnet[id].assigned-addresses statistic when reclaiming
an expired lease.

Finally, it's rather obvious, but not explicitly stated, that all
requirements apply to both v4 and v6.

Tomek