[Dnsmasq-discuss] A (possibly bad) idea: failover in dnsmasq

Simon Kelley simon at thekelleys.org.uk
Sat May 26 11:35:00 BST 2012


On 26/05/12 10:24, Vincent Cadet wrote:
>>> This active-passive scheme shouldn't need any dnsmasq
>> changes, and
>>> arranging to monitor server instances and start a new
>> one when an
>>> existing one goes down is a solved problem: it's
>> exactly what heartbeat
>>> does.
>>>
>>> Building a heartbeat harness to run dnsmasq
>> active-passive and
>>> replicated tyrant (or another database) sure looks like
>> a useful thing
>>> to try, IMHO.
>
> What if there be a heartbeat link in dnsmasq through which the active
> dnsmasq would stream changes (or the whole block of data) to the
> passive instance along with keep-alive probes?

That has attractions: Both dnsmasq instances could provide DNS service 
at all times, and whichever was "master" could provide DHCP, whilst the 
"slave" just keeps it's database up-to-date. The main problem with this 
is the "split brain" scenario, where both instances are up, but they 
can't talk to each other because the network between them is 
partitioned. In that case both acting as masters for their half of the 
network is fine, the problem comes when connectivity returns and the 
lease databases have to be reconciled....

> Something similar to
> Postgres streaming replication in fact. An interruption in the stream
> for more than a programmed delay would then be interpreted as a
> fail-over request. The link would be a socket, serial link,
> whatever.
>

Worth thinking about....


Simon.



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