> Op 25 februari 2017 om 15:45 schreef Adam Carheden <adam.carheden@xxxxxxxxx>: > > > I spoke with the cloud stack guys on IRC yesterday and the only risk is > when libvirtd starts. Ceph is supported only with libvirt. Cloudstack can > only pass one monitor to libvirt even though libvirt can use more. Libvirt > uses that info when it boots, but after that it gets all the monitors from > that initial one, just as you say. If you have to reboot libvirtd when that > monitor is down, that's a problem. But RR DNS would mean just restarting > libvirtd again will probably fix it. It's not the case. Libvirt will simply pass down the hostname down to Qemu, which passes it down to librbd and librados. Librados is the one doing the DNS lookup and get's back: ceph-monitor.example.com AAAA 2001:db8::100 ceph-monitor.example.com AAAA 2001:db8::101 ceph-monitor.example.com AAAA 2001:db8::102 It will try 2001:db8::100 first. If it works, great! It obtains the monmap. If it's down, it will try 2001:db8::101 and 2001:db8::102. After obtaining the monmap everything is good. It's actually easier to use RR-DNS so that you can swap Monitors easily without having to update CloudStack's configuration. Wido > > On Feb 25, 2017 6:56 AM, "Wido den Hollander" <wido@xxxxxxxx> wrote: > > > > Op 24 februari 2017 om 19:48 schreef Adam Carheden < > adam.carheden@xxxxxxxxx>: > > > > > > From the docs for each project: > > > > "When a primary storage outage occurs the hypervisor immediately stops > > all VMs stored on that storage > > device"http://docs.cloudstack.apache.org/projects/ > cloudstack-administration/en/4.8/reliability.html > > > > "CloudStack will only bind to one monitor (You can however create a > > Round Robin DNS record over multiple > > monitors)"http://docs.ceph.com/docs/master/rbd/rbd-cloudstack/ > > > > Doesn't this mean that if the CEPH monitor cloudstack chooses to bind to > > goes down all your VMs stop? If so, that seems pretty risky. > > > > No, it doesn't. librados will failover over to another Monitor. > > > RRDNS is for poor man's load balancing, not HA. I guess it depends on when > > Cloudstack does DNS lookup and if there's some minimum unavailable delay > > before it flags primary storage as offline, but it seems like substituting > > RRDNS for whatever CEPH's internal "find an available monitor" algorithm > is > > is a bad idea. > > No, you are understanding it wrongly. CloudStack doesn't perform the DNS > lookup, this is done by librados on the hypervisor. > > It will receive all Monitors from that DNS lookup and connect to one of > them. As soon as it does it will obtain the monmap and know the full > topology. > > Fully redundant and failover proof. > > Wido > > > > > -- > > Adam Carheden > > _______________________________________________ > > ceph-users mailing list > > ceph-users@xxxxxxxxxxxxxx > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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