SOA is a three letter acronym that created a fervor from the server closet to the executive boardroom. A decade of labor by standards committees, tool vendors, framework builders, consultants, and hucksters made sure SOA became the silver bullet for enterprise architecture.
If I look through the noise for the pragmatic essence of SOA, I see three noble goals:
- Software encapsulation – or the ability to hide complexity behind coarse grained interfaces.
- Software autonomy - or the absolute control of the execution environment and the resources required by software, as well as the freedom to make independent decisions about implementation details.
- Software interoperability – or optimizing for reuse by relying on standard application level communication protocols.
Those three goals are entirely possible with HTTP based services and the ASP.NET WebAPI. The S in SOA doesn't stand for SOAP.
I know many people will say the additional metadata commonly associated with SOA (like WS-Metadata Exchange, WS-Policy, and XML Schema, to name just a few) is also a core part of SOA. I'd argue the metadata was good for vendors who built software to manage the complexity of the metadata.
KISS it goodbye with the WebAPI.