Unlike SOA, which promotes cohesion of services, Microservices promote the principle of isolation of services. Each Microservice should have minimal interaction with other Microservices that are part of the system. This gives the advantage of independent scale and deployment to the Microservices.
Let's redraw the architecture of the car rental company using the Microservices architecture principle:
In the revised architecture, we have created a Microservice corresponding to each domain of the original system. This architecture does away with the integration and orchestration component. Unlike SOA, which requires all services to be connected to an ESB, Microservices can communicate with each other through simple message passing. We will soon look at how Microservices can communicate.
Also, note that we have used the principles of Domain-Driven Design (DDD), which is the principle that should be used for designing a Microservices-based system. A Microservice should never spawn across domains. However, each domain can have multiple Microservices. Microservices avoid communicating with each other and for the most part use the user interface for communication.
In the revised setup, each team can develop and manage a Microservice. Rather than distributing teams around technologies and creating multiple channels of communication, this distribution can increase agility. For instance, adding a new form of payment requires making a change in the payment Microservice and therefore requires communication with only a single team.
Isolation between services makes adoption of Continuous Delivery much simpler. This allows you to safely deploy applications and roll out changes and revert deployments in case of failures.
Since services can be individually versioned and deployed, significant savings are attained in the deployment and testing of Microservices.
