Gentle shutdown feature

[Shawn Routhier]

On Jun 27, 2014, at 8:35 AM, John Wobus wrote:

> Here's our situation:
> We run DHCP-4.1-ESV R8 and we stop and restart the
> server every 2 minutes to reconfigure.  We have about
> 200,000 addresses in dynamic pools and our log
> grows to 20 million plus lines a day.
> 
> There are other similar sites that use the same "stop and
> start frequently" strategy.  I would naturally be concerned
> if the daemons had trouble ever reaching normal state.
> 
> I am surprised at two things:
> (1) A new feature was put into the ESV version?
> I'm wondering why such a thing exists if it is
> handled like that.  Was this considered a bug fix?

Basically - it was on the boundary between a bug and
a new feature.  We didn't realize how disruptive it could
be in some cases.

> 
> (2) I always thought SIGTERM caused the server
> to finish writing the lease file.  I noticed
> significant delays (tenths of a second)
> in dhcpd "term" time a decade ago and attributed
> it to lease file writing.  I'm surprised to hear
> otherwise.
> 
> John Wobus
> Cornell University IT
> 
> On Jun 26, 2014, at 2:13 PM, Shawn Routhier wrote:
> 
>> In the 4.3.0 release cycle we added a feature to gently shutdown
>> clients and servers when they received SIGINT and SIGTERM
>> signals.  This feature was included in the changes back ported to
>> 4.1-ESV and 4.2 and has two side effects that may affect users.
>> This was done to allow any writes to the lease files to complete
>> before the process stops.
>> 
>> When a client receives a SIGINT or SIGTERM signal  the new
>> behavior is to send a release message to the server.
>> 
>> When a server receives a SIGINT or SIGTERM signal "if" failover
>> is in use then when the server is restarted it may go through recover
>> wait for a number of seconds (determined by the server's MCLT
>> setting)  before becoming usable.
>> 
>> 
>> In both of these cases the previous functionality can be gotten
>> by halting the process with a different signal, for example
>> "kill -9 <pid>"
>> 
>> We have received a report objecting to this feature
>> and we are determining the best course of action.
>> 
>> 1) Are you already making use of this feature?  Or would it
>> not be an issue if we disabled it?
>> 
>> 2) Has this feature caused issues for you?
>> 
>> 3) Any other useful comments about this issue?
>> 
>> Shawn Routhier
>> ISC DHCP
>> 
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> 
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