Cloud Computing and Service Models

Three service models, one stack, cut at different heights

Cloud computing delivers computing resources over the internet rather than from hardware the user owns and maintains directly, and the three standard service models, IaaS, PaaS and SaaS, are best understood not as three separate technologies but as the same underlying technology stack, sliced at three different points depending on how much the customer wants to manage themselves versus hand over to the provider.

Infrastructure as a Service (IaaS) delivers the most basic layer: raw computing power, storage and networking, as a service over the internet. The customer still installs and manages their own operating system and applications on top of it; the provider only handles the physical hardware.

Platform as a Service (PaaS) delivers a step higher: a ready-to-use platform for developing, deploying and managing applications, without the customer needing to install or maintain the underlying operating system or development tools themselves.

Software as a Service (SaaS) delivers the highest layer: a finished, ready-to-use application, accessed over the internet, with the customer installing nothing at all on their own machine. Most consumer-facing cloud products, email, office suites, video conferencing, are SaaS.

The pattern worth holding: moving from IaaS to PaaS to SaaS is moving up the stack, and at each step more responsibility shifts from the customer to the provider.

Deployment models: who else is on the same infrastructure

A separate axis from the service models above concerns who the underlying infrastructure is shared with. A public cloud is available to any registered user and is shared across many customers. A private cloud is dedicated to a single organisation, giving it more control and typically more predictable security, at greater cost. A hybrid cloud is a private cloud that can extend into public cloud resources when extra capacity is needed, giving an organisation the control of a private cloud with the elastic scalability of a public one when demand spikes.

MeghRaj: India's own government cloud

MeghRaj, the GI Cloud initiative, is the Government of India's own cloud computing platform, built to provide ICT services via the cloud to departments across the Centre and the states. Over 300 government departments now run on it. MeghRaj is best understood as India choosing a form of private or hybrid cloud for government use specifically, rather than putting citizen and administrative data onto a general public cloud shared with unrelated commercial customers, which connects directly to the deployment-model distinction above: the choice of deployment model here is a genuine governance decision, not just a technical one.

Quick revision points

• IaaS, PaaS, SaaS are one stack cut at three heights, not three technologies. IaaS: raw compute/storage/network, customer manages the OS and apps. PaaS: a ready platform for building and deploying apps, customer manages only the app. SaaS: a finished application, customer manages nothing locally. Moving IaaS to PaaS to SaaS shifts more responsibility to the provider.
• Deployment models: public (shared, open registration), private (dedicated to one organisation), hybrid (a private cloud that extends into public cloud capacity when needed).
• MeghRaj (GI Cloud): India's government cloud platform, 300+ departments, effectively a private/hybrid deployment choice made deliberately for governance reasons rather than a purely technical one.