561dc127bd
Previous fixes restored round robin iteration, but an imbalance remains
when the response tree contains record types other than A or AAAA. Let's
take the following example: the DNS answers two A records and a CNAME.
The response "tree" (which is actually flat, more like a list) may look
as follows, ordered by hash:
- 1st item: first A record with IP 1
- 2nd item: second A record with IP 2
- 3rd item: CNAME record
As a consequence, resolv_get_ip_from_response will iterate as follows,
while the TTL is still valid:
- 1st call: DNS request is done, response tree is created, iteration
starts at the first item, IP 1 is returned.
- 2nd call: cached response tree is used, iteration starts at the second
item, IP 2 is returned.
- 3rd call: cached response tree is used, iteration starts at the third
item, but it's a CNAME, so we continue to the next item, which restarts
iteration at the first item, and IP 1 is returned.
- 4th call: cached response tree is used and iteration restarts at the
beginning, returning IP 1 again.
The 1-2-1-1-2-1-1-2 sequence will repeat, so IP 1 will be used twice as
often as IP 2, creating a strong imbalance. Even with more IP addresses,
the first one by hashing order in the tree will always receive twice the
traffic of the others.
To fix this, set the next iteration item to the one following the selected
IP record, if any. This ensures we never use the same IP twice in a row.
This commit should be backported where 3023e9819 ("BUG/MINOR: resolvers:
Restore round-robin selection on records in DNS answers") is, so as far
as 2.6.
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.