In case you missed it, the first phase of cloud computing has left the building. Thousands of companies are in the cloud. Practically all organizations regardless of size already have production applications in a public, off-premises cloud or a private cloud. Yep. Been there, done that.
And the vast majority of these applications use the classic “SaaS-style” public cloud model. Someone develops a useful service and hosts it on Amazon Web Services (AWS), Microsoft Azure, IBM Cloud Marketplace, Google Cloud Platform (GCP) or one of several other cloud vendors. Accessing this external service is typically performed via a well-defined API. Typically this API invocation is made using a simple REST call (or a convenient library wrapper around a REST call). This request originates from a web browser, native app on a mobile device or some server-side application and traverses the web. Using only port 443 or 80, it connects through a series of firewalls to the actual service running in the external cloud environment. The request is serviced by a process running in a service provider’s computing environment and returns a result to the client application.