that's strange, because the dnsmasq man page explicitly calls out the SIGHUP as a way to reconfigure DHCP hosts entries from a --dhcp-hostsfile parameter. Or are these not the same thing?
On Tue, Apr 30, 2013 at 5:52 PM, Chiradeep Vittal < chiradeep.vit...@citrix.com> wrote: > > > On 4/30/13 3:26 PM, "Dennis Lawler" <dlaw...@gmail.com> wrote: > > >Every time a new VM is started up, there is a 2 second outage in DNS > >services that can cause problems in guest VMs that use the router VM for > >DNS. > > > > > > > >For Cloudstack configurations using both DHCP and DNS services on the > >router > >VM (both implemented with dnsmasq), there is currently a 2 second DNS > >service outage every time a new VM is instantiated > > > > > > > >The source of this outage is in edithosts.sh, which uses "service dnsmasq > >restart" to pick up the freshly added DNS and DHCP entries. > > > >Restarting the dnsmasq service triggers a sleep for 2 seconds after > >killing > >dnsmasq before starting it back up again. > > > > > > > >An obvious solution would be to replace "service dnsmasq restart" with > >"kill > >-s 1 $pid" (SIGHUP) so that dnsmasq reads the new DHCP entries without > >restarting, as in dnsmasq_edithosts.sh (external dhcp). > > > > > >Unfortunately, this solution is flawed because dnsmasq SIGHUP handling > >does > >not expire in-memory DHCP leases in dnsmasq and all leases are infinite by > >default. > > Aha! That's why SIGHUP didn't work consistently. This has been bugging me > for a long time. > > >Thus, this will only work if the guest VM performs a DHCP release on > >shutdown, which cannot always be guaranteed. > > > > > > > >A few possible solutions off the top of my head: > > > >1. Separate DNS and DHCP services. While DHCP services still > >experience an outage during VM, DNS will not necessarily be impacted if > >implemented correctly. > > > >2. Use SIGHUP with dnsmasq and implement a removeDhcpEntry interface > >for network appliances to force a DHCP release whenever a NIC / IP is > >deallocated. This can use dhcp_release to simulate a DHCP release on the > >router VM. > >Catch: dhcp_release is not available for Debian 6.0. The System VM needs > >to > >be updated to at least Debian 7.0, or the dnsmasq-tools .deb from 7.0 > >would > >need to be included in the System VM image. > > There is going to be a new system vm based on 7.0 for the upcoming > release. This should work with earlier releases as well. > https://cwiki.apache.org/confluence/x/UlHVAQ > > > > >3. Change DHCP to have a shorter lease, track de-allocation of IPs > >separately from VM destruction. > >Catch: This may cause occasional IP pool exhaustion depending on > >allocation > >of the guest IP range and the rate of VM destruction / instantiation in > >the > >network. > > > > > > > >Thoughts? > > > >
