It has been stated throughout this book that it mostly aims towards web applications in general, and with web applications come databases. There are many shapes and sizes of databases, from relational to non-relational, and this chapter will focus on relational databases. Books of all shapes from authors of all backgrounds have covered databases; so we will try not to beat the dead horse too much in this chapter, but some of those topics are still relevant when moving into a Cloud-backed infrastructure like AWS.

In a traditional web application, there is the front-end instance (typically the user interface), and the backend database instance. In larger and more complex systems, there are many more systems but they all will interact with one or more databases. These non-database systems can be easily architected to be highly available and are generally cheap to scale out when the load becomes high (cheap in this case means that it can be done either by an...