Introducing events

Events are important constructs in both Azure and Azure application architecture. Events are everywhere within the software ecosystem. Generally, any action that is taken results in an event that can be trapped, and then further action can be taken. To take this discussion forward, it is important to first understand the basics of events.

Events help in capturing the new state of a target resource. A message is a lightweight notification of a condition or a state change. Events are different than messages. Messages are related to business functionality, such as sending order details to another system. They contain raw data and can be large in size. In comparison, events are different; for instance, a virtual machine being stopped is an event. Figure 12.1 demonstrates this transition from the current state to the target state:

Figure 12.1: Transition of a state due to an event

Events can be stored in durable storage as historical...