[Dnsmasq-discuss] Redundant setup with Dnsmasq

Ed W lists at wildgooses.com
Fri Dec 23 12:38:14 GMT 2011


On 22/12/2011 18:58, richardvoigt at gmail.com wrote:
>> To sync the DHCP-Leases to the secondary server, you need to create a
>> ssh-key (ssh-keygen) to copy the lease-file without knowing the ssh-passord.
>>
>> scp 10.0.0.251:/var/dhcp/dnsmasq.leases /var/dhcp/dnsmasq.leases
> Please note that by default, automatic DNS registrations and the list
> of existing DHCP leases are going to be lost during failover.
>
> Copying the dnsmasq.leases file with cron creates a race condition as
> it is not synchronized with dnsmasq updating the file.  I would
> recommend using a external database to store the leases with support
> for atomic updates instead  of letting dnsmasq put them in
> /var/*/dnsmasq.leases.
>
> See the dhcp-script and leasefile-ro options.
>

Seems like there are two interesting opportunities for someone 
sponsoring dnsmasq changes:

1) Atomic updates to the leasefile (or near enough for practical purposes)
2) Re-reading of the leasefile on change (in a way designed to support 
use with a cluster filesystem or manual sync)
3) Some intra-dhcp communication mechanism designed to support high 
availability, eg enhancing dhcp protocol to broadcast change events, 
some kind of master server election (eg see netbios), or something more 
sophisticated eg Paxos (see googles Chubby for implementation ideas)

The basic problem of having multiple overlapping dhcp servers is 
desirable to solve for all dhcp servers, so any general solution would 
ideally be simple and presented as an RFC so that we could get a cross 
platform solution going... (thinking something simple involving 
broadcasts to allow an election process... Technically leases don't need 
to be sync'd, so separate process can handle that)

Cheers

Ed W




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