Revisiting the CQRS pattern

Command Query Responsibility Segregation (CQRS), explored in Chapter 14, Mediator and CQRS Design Patterns, applies the Command Query Separation (CQS) principle. Compared to what we saw in Chapter 14, Mediator and CQRS Design Patterns, we can push CQRS further using microservices or serverless computing. Instead of simply creating a clear separation between commands and queries, we can divide them even more by using multiple microservices and data sources.

CQS is a principle stating that a method should either return data or mutate data, but not both. On the other hand, CQRS suggests using one model to read the data and one model to mutate the data.

Serverless computing is a cloud execution model where the cloud provider manages the servers and allocates the resources on-demand, based on usage. Serverless resources fall into the platform as a service (PaaS) offering.

Let's use IoT again as an example; we were querying the last known location...