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HAProxy - Load balancer
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When leveraging shm-stats-file, global_now_ms and global_now_ns are stored
(and thus shared) inside the shared map, so that all co-processes share
the same clock source.
Since the global_now_{ns,ms} clocks are derived from now_ns, and given
that now_ns is a monotonic clock (hence inconsistent from one host to
another or reset after reboot) special care must be taken to detect
situations where the clock stored in the shared map is inconsistent
with the one from the local process during startup, and cannot be
relied upon anymore. A common situation where the current implementation
fails is resuming from a shared file after reboot: the global_now_ns stored
in the shm-stats-file will be greater than the local now_ns after reboot,
and applying the shared offset doesn't help since it was only relevant to
processes prior to rebooting. Haproxy's clock code doesn't expect that
(once the now offset is applied) global_now_ns > now_ns, and it creates
ambiguous situation where the clock computations (both haproxy oriented
and shm-stats-file oriented) are broken.
To fix the issue, when we detect that the clock stored in the shm is
off by more than SHM_STATS_FILE_HEARTBEAT_TIMEOUT (60s) from the
local now_ns, since this situation is not supposed to happen in normal
environment on the host, we assume that the shm file was previously used
on a different system (or that the current host rebooted).
In this case, we perform a manually adjustment of the now offset so that
the monotonic clock from the current host is consistent again with the
global_now_ns stored in the file. Doing so we can ensure that clock-
dependent objects (such as freq_counters) stored within the map will keep
working as if we just (re)started where we left off when the last process
stopped updating the map.
Normally it is not expected that we update the now offset stored in the
map once the map was already created (because of concurrent accesses to
the file when multiple processes are attached to it), but in this specific
case, we know we are the first process on this host to start working
(again) on the file, thus we update the offset as if we created the
file ourself, while keeping existing content.
It should be backported in 3.3
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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.