DHCP failover - disk full, can not commit to lease file

[Sten Carlsen]

You should monitor the disks, not the log?

Any system that uses disk space on that particular host needs free
space. The systems I have seen warn when less than 10% free disk space
is remaining, that is the point you should act on - free up disk space
or add new disks. This information is not available in dhcp-logs but a
well designed monitoring system will tell you.

Once you see the message from dhcp, the disaster is at the door, knocking.


On 28/05/13 6:25, Louis Lau wrote:
>  
> Yes agree. This can be monitored by monitoring system with some docuentation. Currently we may use HPOV or other monitoring script to monitor the DHCP log. But the output must match exactly or otherwise too many alarm will be triggered. 
>
> We noted that there are subscription service of ISC DHCP, would this cover the documentation for the monitoring part?
>
> And also we want to know are there any application level fault the failover mechanism could handle. We have currently just know that if node down or communication down, the failover will kick in. not sure about what other condition would kick in the failover.
>
> Louis Lau
>  
>  
>
> -----Original Message-----
> From: dhcp-users-bounces+louis_lau=nechk.nec.com.hk at lists.isc.org [mailto:dhcp-users-bounces+louis_lau=nechk.nec.com.hk at lists.isc.org] On Behalf Of Glenn Satchell
> Sent: Tuesday, May 28, 2013 12:02 PM
> To: Users of ISC DHCP
> Subject: Re: DHCP failover - disk full, can not commit to lease file
>
> DHCP is not a monitoring system. Why not use your existing, dedicated monitoring system to detect the failure modes you care about, and get that to trigger failover. This could be simple - turn off the dhcp service, or put it in partner-down mode.
>
> There are many possible scenarios where this would be appropriate, but is this something the dhcp server needs to be able to handle?  Is this the best use of available dhcp developer time?
>
> regards,
> -glenn
>
> On Tue, May 28, 2013 9:27 am, Doug Barton wrote:
>> I could make a pretty good argument that "My disk is full and I cannot 
>> write leases" would be something that should trigger failover.
>>
>> Doug
>>
>>
>> On 05/27/2013 03:56 PM, Steven Carr wrote:
>>> No, your disk is full (and you risk more issues than just DHCP 
>>> problems), DHCPD needs to be able to write the lease information to 
>>> disk, without that that it will not function. The DHCP failover 
>>> protocol does not take into account the resources on the local system 
>>> when assigning DHCP leases, it assumes your resources are adequate 
>>> enough for the job.
>>>
>>>
>>>
>>> On 27 May 2013 19:53, Louis Lau <Louis_Lau at nechk.nec.com.hk> wrote:
>>>> Dear all,
>>>>
>>>> I have two DHCP servers configured as failover peer and the router 
>>>> relay the DHCP/Bootp request to both server. When the system works 
>>>> normaly, a DHCP discover from client will be broadcast to both 
>>>> server and the observed behavour is that both server will offer an 
>>>> DHCP OFFER to the same client, The primary DHCP server shall reply 
>>>> an IP-A managed by the Primary, and the Secondary shall reply an 
>>>> IP-B that is managed by the secondary. Assume the client select IP-A 
>>>> and send an DHCP Request for IP-A to both server.
>>>>
>>>> However recently, primary server disk is full, and in the log there 
>>>> are a lot of
>>>>
>>>> ommit_leases: unable to commit: No space left on device
>>>>
>>>> We observed that the DHCP does not failover to the secondary in this 
>>>> case, and the primary will still response to DHCPDISCOVER and 
>>>> provide a DHCP Offer.  And in this case, we observed that most 
>>>> client does not try the DHCP offer from secondary but most of them 
>>>> choose the IP assigned from the Primary DHCP server.
>>>>
>>>> Is this behaviour normal?
>>>>
>>>> Are there any configuration that can make the server fail to 
>>>> secondary DHCP server for similar case or let the client try the 
>>>> other DHCP OFFER when the first DHCP IP does not have a ACK?
>>>>
>>>> Thanks for your help on this matter.
>>>>
>>>>
>>>> Louis Lau
>> _______________________________________________
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>> dhcp-users at lists.isc.org
>> https://lists.isc.org/mailman/listinfo/dhcp-users
>>
>
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-- 
Best regards

Sten Carlsen

No improvements come from shouting:
       "MALE BOVINE MANURE!!!"

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