SOA and the microservice architecture are architectural styles that structure a system as a set of services. But the communication styles are different. Both are using Inter-service communication due to distributed services. But in SOA, using Enterprise Service Bus, using heavyweight protocols, such as SOAP, WSDL, and XSD protocols.

But in microservices, using message brokers, or direct service-to-service communication, using lightweight protocols such as REST or gRPC. Also Data models are different, SOA using Global data model and shared databases, But Microservices has polyglot databases with database per service pattern.

Another key difference between SOA and the microservice architecture is the size of the services. SOA is typically used to integrate large, complex, monolithic applications. Although services in a microservice architecture almost always much smaller.

As a result, a SOA application usually consists of a few large services, whereas a microservices-based application typically consists of dozens or hundreds of smaller services.