The config file is only read at specific points in time. It is first
read when the buildmaster is launched. Once it is running, there are
various ways to ask it to reload the config file. If you are on the
system hosting the buildmaster, you can send a SIGHUP signal to
it: the buildbot tool has a shortcut for this:
buildbot reconfig BASEDIR
This command will show you all of the lines from twistd.log that relate to the reconfiguration. If there are any problems during the config-file reload, they will be displayed in these lines.
The debug tool (buildbot debugclient --master HOST:PORT) has a
“Reload .cfg” button which will also trigger a reload. In the
future, there will be other ways to accomplish this step (probably a
password-protected button on the web page, as well as a privileged IRC
command).
When reloading the config file, the buildmaster will endeavor to change as little as possible about the running system. For example, although old status targets may be shut down and new ones started up, any status targets that were not changed since the last time the config file was read will be left running and untouched. Likewise any Builders which have not been changed will be left running. If a Builder is modified (say, the build process is changed) while a Build is currently running, that Build will keep running with the old process until it completes. Any previously queued Builds (or Builds which get queued after the reconfig) will use the new process.