Copyright 1993-1994, 1996-1998, 2000, 2003-2009, 2012-2014 The Board of Trustees of the Leland Stanford Junior University. This software is distributed under a BSD-style license. Please see the section License below for more information.
This package is orphaned. Although I believe it is still useful, I no longer use this method of DNS load balancing and am no longer maintaining this package. If you would like to pick up maintenance of it, please feel free. Contact me if you would like this page to redirect to its new home.
lbcd is a daemon that runs on a UNIX system and answers UDP queries with
information about system load, number of logged-on users, uptime, and free
/tmp space. This information can be used to accumulate system status
across a cluster with light-weight queries or can be used as input to a
load-balancing system to choose the best system to which to direct new
incoming connections.
lbcd provides a lightweight way to query a system via unauthenticated UDP
for system load information plus some related information that may be
relevant to determining which system to hand out. It was designed for use
with the lbnamed DNS load
balancer. System load, number
of logged-in users, free /tmp space, and system uptime are always
returned. lbcd can also be configured to probe various local services and
modify the returned weights based on whether those services are reachable,
or to return a static weight for round-robin load balancing.
The information provided isn't particularly sophisticated, and a good hardware load balancer will be able to consider such things as connection latency and responsiveness to make better decisions. However, lbcd with lbnamed works well for smaller scale problems, scales to multiple load balance pools for different services, provides a simple UDP health check service, and is much simpler and cheaper to understand and deploy.
Included in this package is a small client program, lbcdclient, which can query an lbcd server and display a formatted version of the returned information.
It was originally written by Roland Schemers. Larry Schwimmer rewrote it to add protocol version 3 with some additional features and service probing, and then I rewrote it again to update the coding style and use my standard portability layer.
lbcd is written in C, so you'll need a C compiler. It also uses kernel calls to obtain load and uptime information, and at present has only been ported to Linux, Solaris, AIX, various BSD systems, Mac OS X, HP-UX, IRIX, and Tru64. It is primarily tested on Linux. Platforms not listed may require some porting effort, as may old or unusual platforms that aren't regularly tested.
The lbcdclient program requires Perl 5.6 or later and requires the IO::Socket::INET6 module for IPv6 support.
To bootstrap from a Git checkout, or if you change the Automake files and need to regenerate Makefile.in, you will need Automake 1.11 or later. For bootstrap or if you change configure.ac or any of the m4 files it includes and need to regenerate configure or config.h.in, you will need Autoconf 2.64 or later.
You can build and install lbcd with the standard commands:
./configure
make
make install
If you are building from a Git clone, first run ./bootstrap in the
source directory to generate the build files. make install will
probably have to be done as root. Building outside of the source
directory is also supported, if you wish, by creating an empty directory
and then running configure with the correct relative path.
lbcd looks for $sysconfdir/nolbcd and returns the maximum load if that
file is present, allowing one to effectively drop a system out of a
load-balanced pool by touching that file. By default, the path is
/usr/local/etc/nolbcd, but you may want to pass --sysconfdir=/etc to
configure to use /etc/nolbcd.
lbcdclient is written in Perl, so you may have to edit the first line of the script to point to the correct Perl location on your system. It does not use any sophisticated Perl features or add-on modules.
Pass --enable-silent-rules to configure for a quieter build (similar to
the Linux kernel). Use make warnings instead of make to build with
full GCC compiler warnings (requires either GCC or Clang and may require a
relatively current version of the compiler).
You will generally want to start lbcd at system boot. On systemd systems,
unit files are installed by default. On other systems, all that is needed
is a simple init script to start lbcd with the appropriate options or kill
it again. It writes its PID into /var/run/lbcd.pid by default (and this
can be changed with the -P option). On many systems, lbcd will need to
run as root or as a member of particular groups to obtain system load
average and uptime information.
lbcd comes with a test suite, which you can run after building with:
make check
If a test fails, you can run a single test with verbose output via:
tests/runtests -o <name-of-test>
Do this instead of running the test program directly since it will ensure that necessary environment variables are set up.
To run the test suite, Perl 5.6.2 or later is required. The following additional Perl modules will be used if present:
- Test::MinimumVersion
- Test::Perl::Critic
- Test::Pod
- Test::Spelling
- Test::Strict
All are available on CPAN. Those tests will be skipped if the modules are not available.
To enable tests that don't detect functionality problems but are used to
sanity-check the release, set the environment variable RELEASE_TESTING
to a true value. To enable tests that may be sensitive to the local
environment or that produce a lot of false positives without uncovering
many problems, set the environment variable AUTHOR_TESTING to a true
value.
The lbcd web page will always have the current version of this package, the current documentation, and pointers to any additional resources.
I welcome bug reports and patches for this package at eagle@eyrie.org. However, please be aware that I tend to be extremely busy and work projects often take priority. I'll save your report and get to it as soon as I can, but it may take me a couple of months.
lbcd is maintained using Git. You can access the current source on GitHub or by cloning the repository at:
https://git.eyrie.org/git/system/lbcd.git
or view the repository on the web.
The eyrie.org repository is the canonical one, maintained by the author, but using GitHub is probably more convenient for most purposes. Pull requests are gratefully reviewed and normally accepted.
The lbcd package as a whole is covered by the following copyright statement and license:
Copyright 1993-1994, 1996-1998, 2000, 2003-2009, 2012-2014 The Board of Trustees of the Leland Stanford Junior University
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
Some files in this distribution are individually released under different licenses, all of which are compatible with the above general package license but which may require preservation of additional notices. All required notices, and detailed information about the licensing of each file, are recorded in the LICENSE file.
Files covered by a license with an assigned SPDX License Identifier include SPDX-License-Identifier tags to enable automated processing of license information. See https://spdx.org/licenses/ for more information.
For any copyright range specified by files in this package as YYYY-ZZZZ, the range specifies every single year in that closed interval.