With this approach you really want 1 fewer public IP than you have public facing servers. With 2 servers this means 1 IP. DNS is used to distribute the load around, and keepalived is used to move traffic when a server fails. But you always want at least 1 servers worth of spare capacity in your HA environment, otherwise after you fail over the server getting 2X traffic will also die.
Actually that's an oversimplified example, since to distribute the load correctly you'd need n-1 public addresses on each of n servers (with diminishing returns). Thankfully few LB scenarios require more than 1X1 machines. -Richard On Jun 28, 2012, at 6:17 AM, David Coulson <da...@davidcoulson.net> wrote: > Multiple IP addresses are used, and managed by keepalived. > > On 6/28/12 7:11 AM, Thomas Manson wrote: >> Ok, >> >> but then, I don't get where is used DNS Round Robin, if only one IP is >> used. (it may be obvious, sorry ;);) >> >> Regards, >> Thomas. >> >> On Thu, Jun 28, 2012 at 1:08 PM, Türker Sezer <turkerse...@tsdesign.info> >> wrote: >> On Thu, Jun 28, 2012 at 11:59 AM, Manson Thomas <m...@mansonthomas.com> >> wrote: >> > usually a client will cache the IP served by the DNS server, in order to >> > not >> > query each time the DNS system. >> > >> > So how can the client switch to another server once it has resolved one. >> >> Clients dont switch ip address. They connect same ip address. But we >> move ip address to backup or another active instance using keepalived >> so they connect another server using same ip address. >> >> -- >> Türker Sezer >> TS Design Informatics LTD. >> >> http://www.tsdesign.info/ >> > >
