[Dnsmasq-discuss] How does DNSMASQ handle large concurrent configure file updating request requests

[Yongkang You]

Hi Simon,

Thanks for replying. Batching the changes is a very good idea, but it is
not easy to implement in IaaS, since the VMs creation processes are handled
separately.

>From my observation, the burst 10k SIGUSER1 signals will cause dnsmasq
occupying 100% CPUs for several hours. The workload comes from 10k reload
events, although the 10k DHCP config entries have been successfully updated
in first tens of minutes.

I didn't read the code, but just guess. Do you think if there is any
possibility that the event queue doesn't accept other reload events, when
last reload event is not finished.

On Thu, Jan 15, 2015 at 6:10 AM, Simon Kelley <simon at thekelleys.org.uk>
wrote:

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> Dnsmasq  checks for incoming network packets and signals in the same
> event loop, so the maximum delay to DHCP packets will be the time to
> read a configuration file once, even if you send 10000 SIGUSER1
> signals, because the code will interleave handling DHCP and DNS
> packets with the config file reading. Batching changes would be good,
> if you can do it, but I'd not go looking for trouble here.
>
>
> Cheers,
>
> Simon.
>
> On 14/01/15 15:49, Brian Haley wrote:
> > On 01/14/2015 04:48 AM, Yongkang You wrote:
> >> Hi,
> >>
> >> We have a cloud environment which uses DNSMASQ as DHCP/DNS
> >> server; in the cloud, it usually starts lots of VMs concurrently,
> >> for example, 10000 VM; for each VM, we will configure a static
> >> DHCP entry in DNSMASQ configuration and send SIGUSER1 to reload.
> >> we observe DNSMASQ becomes very busy of reloading, for example,
> >> it seems to reload 10000 times if we send for 10000 SIGUSER1.
> >>
> >> Is this expected behavior? Is there any way to avoid this?
> >> because it keep reloading, we don't know if this will effect VM
> >> getting IP address.
> >
> > Just for completeness, is this on Openstack?  I can see that code
> > doesn't buffer anything when a port is plugged-in, so each triggers
> > a reload.  Could maybe tweak things there to wait a few seconds
> > between the HUPs.  I'm not sure it's a bug in dnsmasq though.
> >
> > -Brian
> >
> > _______________________________________________ Dnsmasq-discuss
> > mailing list Dnsmasq-discuss at lists.thekelleys.org.uk
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> >
>
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-- 
Yongkang You
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