In this chapter, we have understood the difference between different types of database and learned about the key features of MongoDB and Redis. We also persisted our application's data using these databases and used dependency injection to make our application more flexible. We also learned how to configure our development and integration environments to use appropriate database instances.

Persistence may be considered the bottom layer of our system. In the next chapter, we'll introduce real-time client/server communication into our application. This frontend functionality means focusing more on the top layer of our system. However, we'll also see Redis playing an important role in supporting this functionality.