There are definitely areas where microservices and SOA have synergies. In the end both approaches pursue the goal of separating applications into services. Such a step can be helpful when migrating an application to microservices: When the application is split into SOA services, individual services can be replaced or supplemented by microservices. Certain calls can be processed by a microservice while other calls are still processed by the application. This enables the migration of applications and the implementation of microservices in a step-by-step manner.
Figure 6.5 shows an example: The uppermost service of CRM is supplemented by a microservice. This microservice now takes all calls and can, if necessary, call the CRM. The second CRM service is completely replaced by a microservice. Using this approach, new functionality can be added to the CRM. At the same time, it is not necessary to reimplement the entire CRM; instead, microservices can complement it at selected places. Section 7.6 presents additional approaches to how legacy applications can be replaced by microservices.