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When using hash-based load balancing, requests are always assigned to the server corresponding to the hash bucket for the balancing key, without taking maxconn or maxqueue into account, unlike in other load balancing methods like 'first'. This adds a new backend directive that can be used to take maxconn and possibly maxqueue in that context. This can be used when hashing is desired to achieve cache locality, but sending requests to a different server is preferable to queuing for a long time or failing requests when the initial server is saturated. By default, affinity is preserved as was the case previously. When 'hash-preserve-affinity' is set to 'maxqueue', servers are considered successively in the order of the hash ring until a server that does not have a full queue is found. When 'maxconn' is set on a server, queueing cannot be disabled, as 'maxqueue=0' means unlimited. To support picking a different server when a server is at 'maxconn' irrespective of the queue, 'hash-preserve-affinity' can be set to 'maxconn'.
HAProxy
HAProxy is a free, very fast and reliable reverse-proxy offering high availability, load balancing, and proxying for TCP and HTTP-based applications.
Installation
The INSTALL file describes how to build HAProxy. A list of packages is also available on the wiki.
Getting help
The discourse and the mailing-list are available for questions or configuration assistance. You can also use the slack or IRC channel. Please don't use the issue tracker for these.
The issue tracker is only for bug reports or feature requests.
Documentation
The HAProxy documentation has been split into a number of different files for ease of use. It is available in text format as well as HTML. The wiki is also meant to replace the old architecture guide.
Please refer to the following files depending on what you're looking for:
- INSTALL for instructions on how to build and install HAProxy
- BRANCHES to understand the project's life cycle and what version to use
- LICENSE for the project's license
- CONTRIBUTING for the process to follow to submit contributions
The more detailed documentation is located into the doc/ directory:
- doc/intro.txt for a quick introduction on HAProxy
- doc/configuration.txt for the configuration's reference manual
- doc/lua.txt for the Lua's reference manual
- doc/SPOE.txt for how to use the SPOE engine
- doc/network-namespaces.txt for how to use network namespaces under Linux
- doc/management.txt for the management guide
- doc/regression-testing.txt for how to use the regression testing suite
- doc/peers.txt for the peers protocol reference
- doc/coding-style.txt for how to adopt HAProxy's coding style
- doc/internals for developer-specific documentation (not all up to date)
License
HAProxy is licensed under GPL 2 or any later version, the headers under LGPL 2.1. See the LICENSE file for a more detailed explanation.