When building applications using service-oriented architecture, you have to pick the protocol to use to communicate between your services. There are a variety of protocols available out there. You could also create your own, though, in most cases, it is not a good idea.
The HTTP protocol has been the Web standard for the last 25 years, and it does not seem like it is about to change anytime soon. It certainly has a few drawbacks but also has the amazing advantages being massively deployed, and it is simple to understand, and simple to debug for humans. It is also cache-able and easy to transport on most networks; it is rarely blocked. The number of tools surrounding HTTP is huge, making it a perfect candidate for rapid development and easy debugging.
REST API
A REST Web service (based on HTTP) has the advantage of being stateless.
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