In this chapter, we learned how to combine the power of Apache Spark, Apache Kafka, Akka, and MongoDB, which together allow us to compose a complete pipeline. We formed a minimal but complete system that gives us interesting information from a stream of data, continually. We did a hands-on exercise with Spark Streaming, and created a SessionDataReceiver class that listens to Kafka messages, and produces some useful output. In the next chapter, we will discuss a very common application of recommendation systems.