Hi Malcolm, On Fri, Jan 16, 2009 at 02:48:18PM +0000, Malcolm Turnbull wrote: > The manual states that when using balance source: > > "The source IP address is hashed and divided by the total > weight of the running servers to designate which server will > receive the request. This ensures that the same client IP > address will always reach the same server as long as no > server goes down or up. If the hash result changes due to the > number of running servers changing, many clients will be > directed to a different server. This algorithm is generally > used in TCP mode where no cookie may be inserted. It may also > be used on the Internet to provide a best-effort stickyness > to clients which refuse session cookies. This algorithm is > static, which means that changing a server's weight on the > fly will have no effect." > > > Does this mean that if say 1 server out of a cluster of 5 servers > fails, then it is likely > that the hash result changes and lots of the clients could potentially > loose their session? (i..e hit the wrong server because the hash has > changed)
Absolutely. That's why hashing should only be used for cache optimization but not when strong persistency is required in case of server failure (cookies are far better then). Regards, Willy
