awx/docs/debugging.md

Debugging

Remote Debugging

Python processes in Tower's development environment are kept running in the background via supervisord. As such, interacting with them via Python's standard pdb.set_trace() isn't possible.

Bundled in our container environment is a remote debugging tool, rdb. You can use it to set remote breakpoints in Tower code and debug interactively over a telnet session:

    # awx/main/tasks.py

    class SomeTask(awx.main.tasks.BaseTask):

        def run(self, pk, **kwargs):
            # This will set a breakpoint and open an interactive Python
            # debugger exposed on a random port between 6899-6999.  The chosen
            # port will be reported as a warning in the Tower logs, e.g.,
            #
            # [2017-01-30 22:26:04,366: WARNING/Worker-11] Remote Debugger:6900: Please telnet into 0.0.0.0 6900.
            #
            # You can access it from your host machine using telnet:
            #
            # $ telnet localhost <port>
            import rdb
            rdb.set_trace()

Keep in mind that when you interactively debug in this way, any process that encounters a breakpoint will wait until an active client is established (it won't handle additional tasks) and concludes the debugging session with a continue command.

To simplify remote debugging session management, Tower's development environment comes with tooling that can automatically discover open remote debugging sessions and automatically connect to them. From your host machine (i.e., outside of the development container), you can run:

make rdb

This will open a Python process that listens for new debugger sessions and automatically connects to them for you.