What is Petrel?

All Python topologies in this book rely on an open source Python library called Petrel. If you have prior experience with Storm, you may recall that there is a GitHub project called storm-starter that includes examples of using Storm with various languages (you can find the latest version of storm-starter at https://github.com/apache/storm/tree/master/examples/storm-starter). The storm-starter project includes a module called storm.py, which allows you to implement Storm topologies in Python. Given the availability of storm.py, is it really necessary to use another library? While it is certainly possible to build topologies using storm.py, it lacks some important features. To work around those gaps, a developer must use languages and tools that won't be familiar to most Python developers. If you are already familiar with these tools and do not mind juggling multiple technology stacks as you work with Storm, you may be happy with storm.py. But most developers who are new to...