561319bd1c
The crappy epoll API stroke again with reloads and transferred FDs. Indeed, when listening sockets are retrieved by a new worker from a previous one, and the old one finally stops listening on them, it closes the FDs. But in this case, since the sockets themselves were not closed, epoll will not unregister them and will continue to report new activity for these in the old process, which can only observe, count an fd_poll_drop event and not unregister them since they're not reachable anymore. The unfortunate effect is that long-lasting old processes are woken up at the same rate as the new process when accepting new connections, and can waste a lot of CPU. Accept rates divided by 8 were observed on a small test involving a slow transfer on 10 connections facing a reload every second so that 10 processes were busy dealing with them while another process was hammering the service with new connections. Fortunately, years ago we implemented a flag FD_CLONED exactly for similar purposes. Let's simply mark transferred FDs with FD_CLONED so that the process knows that these ones require special treatment and have to be manually unregistered before being closed. This does the job fine, now old processes correctly unregister the FD before closing it and no longer receive accept events for the new process. This needs to be backported to all stable versions. It only affects epoll, as usual, and this time in combination with transferred FDs (typically reloads in master-worker mode). Thanks to Damien Claisse for providing all detailed measurements and statistics allowing to understand and reproduce the problem.
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.