Twisted programs usually work with twisted.application.service.Application. This class usually holds all persistent configuration of a running server, such as:
ports to bind to,
places where connections to must be kept or attempted,
periodic actions to do,
and almost everything else to do with your Application.
It is the root object in a tree of services implementing twisted.application.service.IService.
Other howtos describe how to write custom code for Applications, but this one describes how to use already written code (which can be part of Twisted or from a third-party Twisted plugin developer).
The Twisted distribution comes with an important tool to deal with Applications: twistd(1).
Applications are just Python objects, which can be created and manipulated in the same ways as any other object.
The Twisted Daemon is a program that knows how to run Applications.
Strictly speaking, twistd is not necessary.
Fetching the application, getting the IService component, calling startService(), scheduling stopService() when the reactor shuts down, and then calling reactor.run() could be done manually.
However, twistd supplies many options which are highly useful for program set up:
choosing a reactor (for more on reactors, see Choosing a Reactor),
logging configuration (see the logger documentation for more),
daemonizing (forking to the background),
and more.
twistd supports all Applications mentioned above – and an additional one.
Sometimes it is convenient to write the code for building a class in straight Python.
One big source of such Python files is the examples directory.
When a straight Python file which defines an Application object called application is used, use the -y option.
When twistd runs, it records its process id in a twistd.pid file (this can be configured via a command line switch).
In order to shutdown the twistd process, kill that pid.
The usual way to do this would be:
kill `cat twistd.pid`
To prevent twistd from daemonizing, you can pass it the --no-daemon option (or -n, in conjunction with other short options).
As always, the gory details are in the manual page.
If you have an Application that runs with twistd, you can deploy it on RedHat Linux or Debian GNU/Linux based systems using the tap2deb or tap2rpm tools.
These take a Twisted Application file (of any of the supported formats — Python source, XML or pickle), and build a Debian or RPM package (respectively) that installs the Application as a system service.
The package includes the Application file, a default /etc/init.d/ script that starts and stops the process with twistd, and post-installation scripts that configure the Application to be run in the appropriate init levels.
Note
tap2rpm and tap2deb do not package your entire application and dependent code, just the Twisted Application file.
You will need to find some other way to package your Python code, such as distutils’ bdist_rpm command.
For more savvy users, these tools also generate the source package, allowing you to modify and polish things which automated software cannot detect (such as dependencies or relationships to virtual packages).