Round robin is not the same as random. If a host name has 4 A records, then most DNS servers (if not all) will return it round-robin. So first a.a.a.1, then a.a.a.2, then a.a.a.1, then a.a.a.2, etc.. Of course there are multiple dns servers involved and thousands of clients over the world, but in the end we almost always get a perfect 25-25-25-25 balancing.
-- With kind regards, Angelo Höngens Systems Administrator ------------------------------------------ NetMatch tourism internet software solutions Ringbaan Oost 2b 5013 CA Tilburg T: +31 (0)13 5811088 F: +31 (0)13 5821239 mailto:[email protected] http://www.netmatch.nl ------------------------------------------ > -----Original Message----- > From: David [mailto:[email protected]] > Sent: donderdag 6 januari 2011 9:45 > To: [email protected] > Subject: Re: Haproxy failover: DNS RR vs Virtual IP (heartbeat, > keepalived) > > On 01/06/2011 05:01 PM, Angelo Höngens wrote: > > (sorry for top posting, damn Outlook) > > > > Just to second Willy's story, this is how a lot of people do it, > including us. We use pacemaker for high availability, and dnr rr for > loadbalancing. > > > > For example we have a 4-node cluster running varnish and haproxy. In > this case I have 4 virtual ipv4-addresses and 4 virtual ipv6 addresses > on the cluster. We use pacemaker to keep the virtual ip's up, and we > use dns round-robin to balance the load. We get nice equal load > balancing this way, and if a node is down (or I want to do > maintenance), the vip's move to other nodes, and they take the extra > load. > > > > Thanks for the information. Both Willy and you refer to DNS RR as a > load > balancing solution, but I don't really understand that point: if > caching, etc... means hostname->load balancer resolution is random, the > load balancing will likely be very unbalanced, no ? > > cheers, > > David
