2 Commits

Author	SHA1	Message	Date
Willy Tarreau	59884a646c	MINOR: lb: allow redispatch when using consistent hash ... Redispatch traditionally only worked for cookie based persistence. Adding redispatch support for consistent hash based persistence - also update docs. Reported by Oskar Stenman on discourse: https://discourse.haproxy.org/t/balance-uri-consistent-hashing-redispatch-3-not-redispatching/3344 Should be backported to 1.8. Cc: Lukas Tribus <lukas@ltri.eu>	2019-01-02 20:22:17 +01:00
Willy Tarreau	6b2e11be1e	[MEDIUM] backend: implement consistent hashing variation ... Consistent hashing provides some interesting advantages over common hashing. It avoids full redistribution in case of a server failure, or when expanding the farm. This has a cost however, the hashing is far from being perfect, as we associate a server to a request by searching the server with the closest key in a tree. Since servers appear multiple times based on their weights, it is recommended to use weights larger than approximately 10-20 in order to smoothen the distribution a bit. In some cases, playing with weights will be the only solution to make a server appear more often and increase chances of being picked, so stats are very important with consistent hashing. In order to indicate the type of hashing, use : hash-type map-based (default, old one) hash-type consistent (new one) Consistent hashing can make sense in a cache farm, in order not to redistribute everyone when a cache changes state. It could also probably be used for long sessions such as terminal sessions, though that has not be attempted yet. More details on this method of hashing here : http://www.spiteful.com/2008/03/17/programmers-toolbox-part-3-consistent-hashing/	2009-10-09 07:17:58 +02:00