Writing and running small- or medium-sized distributed applications in Python is not hard. There are many high-quality frameworks that we can leverage among others, for example, Celery, Pyro, various job schedulers, Twisted, MPI bindings (not discussed in this book), or the multiprocessing module in the standard library.

The real difficulty, however, lies in monitoring and debugging our applications, especially because a large fraction of our code runs concurrently on many different, often remote, computers.

The most insidious bugs are those that end up producing incorrect results (for example, because of data becoming corrupted along the way) rather than raising an exception, which most frameworks are able to catch and bubble up.

The monitoring and debugging tools that we can use with Python code are, sadly, not as sophisticated as the frameworks and libraries we use to develop that same code. The consequence is that large teams end up developing their own, oftentimes, very specialized...