The problem with the term Cloud, in its popular usage in IT, is that it’s intended to obfuscate complexity to help a varied audience grapple with fundamental shifts in the industry. It’s a marketing term leveraged to sell products, rather than a technical classification described by the IEEE. Real clouds are amorphous and ethereal, and those attributes intentionally drive the metaphors inherent ambiguity. The fundamental point is that something provided to you by the Cloud is flexible and easy, in some way managed for you, and at least initially, hosted by the provider rather than in your own datacenter.
That last bit has evolved as on-prem companies, like VMware, have driven the “Private Cloud” industry, which refers to high degrees of flexibility, virtualization, and managed services that are hosted in your company’s privately-owned datacenters.
A Tale of Two Meanings
A more concrete way to break down the term “Cloud” is with the variable acronym “XaaS,” which stands for “X as a Service” where the X can be one of several words. One of the most common words for X is “software,” so “Software as a Service,” or “SaaS.” A good example of SaaS is Salesforce, another is Google Docs. These applications (CRM and Word Processing) have typically been handled by software installed on your computer, and/or in your datacenter. Now instead, you can simply use them through a combination of your browser and mobile apps.
That gives rise to one of the two major meanings of “Cloud,” which is SaaS software that originally ran almost exclusively in browsers, and the software creator hosted the servers and databases that it ran on. These days most SaaS software has added mobile apps, but even through 2018, SaaS is mostly understood to be hosted by the provider, and never “on-prem” (on premises – that is in your company’s own datacenter).
The other branch of Cloud definitions falls under IaaS, “Infrastructure as a Service.” This traditionally involved hosting your own custom-written software (or perhaps COTS, “commercial off the shelf” software) on servers from cloud providers such as AWS, GCP, and Azure. As companies like VMware and Redhat have popularized the idea of Private Clouds (similar features to AWS, etc, but hosted on privately owned datacenters), we now tend to talk about AWS, GCP, and Azure as the Public Cloud.
Further Down the Rabbit Hole
While SaaS has remained fairly unified, IaaS has been broken down into several subcategories. To an extent, IaaS itself has evolved to be a mere subcategory of its previous glory. Now we speak of IaaS as raw virtualized resources such as VMs (Virtual Machines), VPCs (Virtual Private Clouds), and cloud storage. And we refer to PaaS as more managed services, like Heroku where you just provide the application code and a few details about how it should be hosted, and the platform manages the servers and even release process for you. We call that PaaS, Platform as a Service.
Recently a new XaaS has arisen, FaaS, Functions as a Service, for example AWS Lambda or GCP Cloud Functions. These are the most highly managed of all, so much so they are strangely called “Serverless.” Not because your code doesn’t run on servers, of course it does, but it’s been so completely abstracted away from you as the developer/operator, that you don’t even have to think about the servers that are running it. In reality, you probably should consider how it’s run and the inherent tradeoffs. FaaS services basically allow you to take some server side code (like Node.js) and attach it to an endpoint (a URL for a specific API method).
While SaaS has remained relatively static, IaaS has evolved into a variety of XaaS categories, both on-prem and in Public Cloud. One final note – most large companies these days are using a combination of Private Cloud solutions like VMware, and multiple Public Cloud solutions like AWS and GCP. The resulting cross-cloud infrastructure has come to be referred to as the Hybrid Cloud.
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