Cloud computing is the delivery of compute, storage, networking and higher-level services as an on-demand utility — provisioned through an API, billed by consumption, and released when no longer needed. The defining shift is not that the hardware belongs to someone else. It is that capacity becomes a runtime decision: a network, a database or a hundred machines are things you request in seconds rather than things you procure in quarters.
Three service models describe how much of the stack the provider operates. Infrastructure as a Service hands you virtual machines, block storage, virtual networks and load balancers, and leaves everything from the operating system upwards to you. Platform as a Service takes the runtime as well, so you deploy an application rather than a server. Managed data services and functions go further, until you supply code and an event source and operate nothing at all. Cutting the other way, the deployment models — public, private, hybrid and multi-cloud — describe where capacity physically sits and who holds the keys.
Everything genuinely difficult about cloud computing lives underneath those definitions. The shared responsibility model decides which failures are yours and which are the provider's. Identity, not the network edge, is the real perimeter. Regions and availability zones are the unit of blast radius, and the bill scales with carelessness as readily as with growth. AWS, Azure and Google Cloud differ in naming and in detail, but the primitives — accounts or projects, IAM, virtual networks, managed compute, object storage, managed databases, audit logging — map across all three. That mapping is what makes cloud skill portable, and it is what a fundamentals course has to teach rather than a single provider's menu.
Why this skill matters now
Almost every organisation now runs something in a public cloud, and a large number run in more than one — through acquisition, through a data-residency requirement, or because one team picked a managed service the rest of the estate does not use. The result is that engineers are expected to reason across providers rather than memorise one console.
The hiring gap is rarely about a specific service. It is about the concepts that keep appearing under different names: how identity federates, why a subnet without a route to a NAT gateway breaks a private workload, what a multi-AZ deployment actually protects against, when a managed database is cheaper than an unmanaged one and when it is not, and how a landing zone stops account sprawl before it starts. Those are transferable and they are what separates someone who can operate a cloud from someone who can follow a tutorial.
There is also a cost dimension that has become sharply commercial. Cloud spend is now one of the largest lines in many IT budgets, and most of the waste is architectural rather than accidental — the wrong storage class, an instance family chosen once and never revisited, egress nobody modelled. Engineers who can explain the bill are unusually valuable.