In this chapter, I describe how web applications are engineered and the common technologies they rely upon. Applications today provide a rich user experience through client-side processing and server APIs supporting mobile applications, desktop browsers, and third-party integrations.
System components are increasingly decoupled to foster scalability (e.g., load balancers, application servers, message queuing services, and key-value stores), which introduce risk when third-party services are used. In 2013, for example, MongoHQ suffered a compromise resulting in customer database instances being accessed.1
Web Application Types
Application categories include retail, banking, gambling, social networking, and information sites (e.g., blogs and news outlets). Consider a standalone web server providing marketing content through a content management system (CMS), as demonstrated by Figure 12-1. Browsers interact with the site over plaintext HTTP, and the application is hosted on a single server.
Figure 12-1. A standalone web application
Large web applications (e.g., Facebook, eBay, and banking sites) are complex; utilizing content delivery networks (CDNs) and supporting native mobile applications, as shown in Figure 12-2. Components run across multiple tiers, using various protocols and data formats.
Figure 12-2. A complex web application
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