SOA stands for Service-Oriented Architecture, a flexible set of design principles that allow multiple separate systems from several business domains to inter-operate.
Service orientation is a paradigm that frames what you do.
Service-oriented architecture (SOA) is a type of architecture
that results from applying service orientation.
([From soa-manifesto.org] )
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For a profession that stresses the importance of naming things well, we’ve done ourselves a disservice with microservices. The problem is that that there is nothing inherently “micro” about microservices. Microservices do not have to be small. Some are, but size is relative and there’s no standard of unit of measure across organizations.
As the number of your services expands you're going to need to start thinking about how to organize them. Applying these two design patterns can help, provided you understand all their variations.
So if you work for a company that scales or has scaled like that at any point in their history, there comes a point when someone says the following: “It will never get easier to split into services”