d624aceaef
There's still a big architectural limitation in the dns/resolvers code regarding threads: resolvers run as a task that is scheduled to run anywhere, and each NS dgram socket is bound to any thread of the same thread group as the initiating thread. This becomes a big problem when dealing with multiple nameservers because responses arrive on any thread, start by locking the resolvers section, and other threads dealing with responses are just stuck waiting for the lock to disappear. This means that most of the time is exclusively spent causing contention. The process_resolvers() function also also suffers from this contention but apparently less often. It turns out that the nameserver sockets are created during emission of the first packet, triggered from the resolvers task. The present patch exploits this to stick all sockets to the calling thread instead of any thread. This way there is no longer any contention between multiple nameservers of a same resolvers section. Tests with a section having 10 name servers showed that the CPU usage dropped from 38 to about 10%, or almost by a factor of 4. Note that TCP resolvers do not offer this possibility because the tasks that manage the applets are created earlier to run anywhere during config parsing. This might possibly be refined later, e.g. by changing the task's affinity when it first runs. The change was kept fairly minimal to permit a backport once enough testing is conducted on it. It could address a significant part of the trouble reported by Felipe in GH issue #3101.
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.