5288b39011
when dns session callback (dns_session_release()) is called upon error
(ie: when some pending queries were not sent), we try our best to
re-create the applet in order to preserve the pending queries and give
them a chance to be retried. This is done at the end of
dns_session_release().
However, doing so exposes to an issue: if the error preventing queries
from being sent is still encountered over and over the dns session could
stay there indefinitely. Meanwhile, other dns sessions may be created on
the same dns_stream_server periodically. If previous failing dns sessions
don't terminate but we also keep creating new ones, we end up accumulating
failing sessions on a given dns_stream_server, which can eventually cause
ressource shortage.
This issue was found when trying to address ("BUG/MINOR: dns: add tempo
between 2 connection attempts for dns servers")
To fix it, we track the number of failed consecutive sessions for a given
dns server. When we reach the threshold (set to 100), we consider that the
link to the dns server is broken (at least temporarily) and we force
dns_session_new() to fail, so that we stop creating new sessions until one
of the existing one eventually succeeds.
A workaround for this fix consists in setting the "maxconn" parameter on
nameserver directive (under resolvers section) to a reasonnable value so
that no more than "maxconn" sessions may co-exist on the same server at
a given time.
This may be backported to all stable versions.
("CLEANUP: dns: remove unused dns_stream_server struct member") may be
backported to ease the backport.
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.