lbcd 3.5.0

This turned out to be a more substantial release than I was originally planning.

lbcd is a small daemon that listens to UDP queries and returns system load and usage information and, optionally, service availability. It's designed to work with a software DNS-based load-balancing system that we use at Stanford (lbnamed), but it can also be used in other situations where you want to easily and quickly query the load of systems remotely.

Debian is currently debating which new init system to adopt, and lbcd was my test package for adding upstart and systemd support. The goal was to add proper, full support as described by upstream, making use of all relevant features, so that I could get some experience with a complete integration. That is complete in this version: lbcd now supports both systemd's and upstart's readiness synchronization mechanisms (using a -Z flag to raise SIGSTOP for upstart) and supports socket activation with systemd. (upstart's socket activation support is missing numerous features, including IPv6 support and, fatally, SOCK_DGRAM support.) It also installs systemd unit files directly when built on a system with systemd support, which should make life easier for use on Red Hat versions later regardless of what happens with Debian.

Of course, while doing that, I kept running across other things that needed to be fixed. For example, systemd's socket activation provides proper support for IPv6, so lbcd should as well. That's now present; that was something I'd been planning on doing for some time. It also supports a -f option to run in the foreground but still log to syslog, something needed by both upstart and systemd to avoid having to use PID files.

Since PID files are no longer necessary, lbcd no longer writes one by default (an idiosyncratic choice made by the previous maintainer), and also drops the -s and -r options to stop and restart itself. Adding these to each daemon was an interesting approach, but I think it's better to leave this to the init system.

While working on the code, I discovered that lbcd allowed the client to request any of the built-in service probes be run, which meant that a client could cause TCP connects to random local services. While this probably couldn't do any harm other than a DoS attack, it still seemed like a bad idea, and was a "feature" I didn't realize was there. Now, only services specified with the -w or -a options may be queried by a client.

I also finally implemented the -l option, which logs each client query, and improved lbcd's recognition of whether someone is on console to allow for modern display manager sessions.

The simple client included in the package, lbcdclient, has been completely rewritten using modern Perl. It supports long options, setting the timeout, setting the port, and returns an error on timeout. It no longer supports multiple servers to query on the command line, since the output just gets confusing and I don't think anyone used this feature. It also now supports IPv6 if IO::Socket::INET6 is available.

Finally, a typo that prevented compilation on Mac OS X has been fixed.

You can get the latest version from the lbcd distribution page.