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HAProxy - Load balancer
cd994407a9
For inet families (IP4/IP6), it is expected that server's addr/port might
be updated at runtime from DNS, cli or lua for instance.
Such updates were performed under the server's lock.
Unfortunately, most readers such as backend.c or sink.c perform the read
without taking server's lock because they can't afford slowing down their
processing for a type of event which is normally rare. But this could
result in bad values being read for the server addr:svc_port tuple (ie:
during connection etablishment) as a result of concurrent updates from
external components, which can obviously cause some undesirable effects.
Instead of slowing the readers down, as we consider server's addr changes
are relatively rare, we take another approach and try to update the
addr:port atomically by performing changes under full thread isolation
when a new change is requested. The changes are performed by a dedicated
task which takes care of isolating the current thread and doesn't depend
on other threads (independent code path) to protect against dead locks.
As such, server's addr:port changes will now be performed atomically, but
they will not be processed instantly, they will be translated to events
that the dedicated task will pick up from time to time to apply the
pending changes.
This bug existed for a very long time and has never been reported so
far. It was discovered by reading the code during the implementation
of log backend ("mode log" in backends). As it involves changes in
sensitive areas as well as thread isolation, it is probably not
worth considering backporting it for now, unless it is proven that it
will help to solve bugs that are actually encountered in the field.
This patch depends on:
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| src | ||
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| .cirrus.yml | ||
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| CONTRIBUTING | ||
| INSTALL | ||
| LICENSE | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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The HAProxy documentation has been split into a number of different files for ease of use. 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)