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A recent patch was introduced to fix a rare race condition in idle connection code which would result in a crash. The issue is when MUX IO handler run on top of connection moved in the purgeable list. The connection would be considered as present in the idle list instead, and reinserted in it at the end of the handler while still in the purge list. 096999ee208b8ae306983bc3fd677517d05948d2 BUG/MEDIUM: connections: permit to permanently remove an idle conn This patch solves the described issue. However, it introduces another bug as it may clear connection flag when removing a connection from its parent list. However, these flags now serve primarily as a status which indicate that the connection is accounted by the server. When a backend connection is freed, server idle/used counters are decremented accordingly to these flags. With the above patch, an incorrect counter could be adjusted and thus wrapping would occured. The first impact of this bug is that it may distort the estimated number of connections needed by servers, which would result either in poor reuse rate or too many idle connections kept. Another noticeable impact is that it may prevent server deletion. The main problem of the original and current issues is that connection flags are misinterpreted as telling if a connection is present in the idle list. As already described here, in fact these flags are solely a status which indicate that the connection is accounted in server counters. Thus, here are the definitive conclusion that can be learned here : * (conn->flags & CO_FL_LIST_MASK) == 1: the connection is accounted by the server it may or may not be present in the idle list * (conn->flags & CO_FL_LIST_MASK) == 0 the connection is not accounted and not present in idle list The discussion above does not mention session list, but a similar pattern can be observed when CO_FL_SESS_IDLE flag is set. To keep the original issue solved and fix the current one, IO MUX handlers prologue are rewritten. Now, flags are not checked anymore for list appartenance and LIST_INLIST macro is used instead. This is definitely clearer with conn_in_list purpose here. On IO MUX handlers end, conn idle flags may be checked if conn_in_list was true, to reinsert the connection either in idle or safe list. This is considered safe as no function should modify idle flags when a connection is not stored in a list, except during conn_free() operation. This patch must be backported to every stable versions after revert of the above commit. It should be appliable up to 3.0 without any issue. On 2.8 and below, <idle_list> connection member does not exist. It should be safe to check <leaf_p> tree node as a replacement.
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.