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Welcome back. In lesson one, we defined cloud computing. Now we'll answer two questions that come

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up again and again on the exam. First: how much of the technology stack do you manage,

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and how much does the provider manage? That's the service model. Second:

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where do your workloads run: in the cloud, in your own data center, or both?

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That's the deployment model.

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Every application sits on a stack of layers. At the bottom are the network and the data center

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building, then servers and storage, virtualization, the operating system,

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the runtime your code needs, your data, and finally the application itself.

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When the online store runs in its own data center, it manages every one of these layers,

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from power and cooling all the way up to its own code.

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With infrastructure as a service, or IaaS, AWS manages the physical layers:

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the data center, the network, the servers and storage, and the virtualization that turns them

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into virtual machines. You manage everything from the operating system up.

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Amazon EC2 is the classic example. The store can rent virtual servers in minutes and still keep

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full control of the operating system and software.

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With platform as a service, or PaaS, the provider also manages the operating system and the runtime.

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You bring your application and your data, and the platform handles provisioning,

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patching and scaling. AWS Elastic Beanstalk works this way: the store uploads its code,

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and Elastic Beanstalk runs it. You give up some control over the servers,

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but there's far less to manage.

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With software as a service, or SaaS, you use a finished application that the provider runs completely,

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usually in a web browser. Think of web-based email or customer relationship management software.

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The store just signs in and uses it. There are no servers, patches or code to manage.

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You do still control your own data, and who in your company can access it.

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Here's the pattern to remember. Moving from left to right, the provider manages more and you manage

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less. IaaS gives you the most control and the most responsibility. SaaS gives you the least to

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manage, but also the least control. PaaS sits in the middle. The right choice depends on how much

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control a workload really needs.

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Now, where do workloads run? There are three deployment models. In a cloud deployment,

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every part of the application runs in the cloud. Applications are either built there or migrated

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there from existing infrastructure. If the store moves its website, database and file storage

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to AWS and closes its server room, that's a cloud deployment.

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A hybrid deployment connects cloud resources with infrastructure that isn't in the cloud,

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usually an existing data center, over a private network link. Companies choose hybrid when legacy

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systems are hard to move, when rules require certain data to stay in their own facilities,

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or while they migrate step by step. The store might keep its warehouse system on premises and

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run its website on AWS.

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In an on-premises deployment, sometimes called a private cloud, everything runs in the company's

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own data center, using virtualization and resource management tools. It provides dedicated resources

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and direct control over the hardware. But the company still buys capacity up front and maintains

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everything itself, so most of the benefits of cloud computing don't apply.

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On the exam, look for the clues. Full control of the operating system points to IaaS.

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Deploying code without managing servers points to PaaS. Ready-to-use software points to SaaS.

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Some systems on premises, connected to the cloud, means hybrid. Everything in the cloud is a cloud

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deployment. And virtualization in your own data center is on-premises, or private cloud.

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To recap: IaaS, PaaS and SaaS describe how much the provider manages, from just the infrastructure,

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to the platform, to the whole application. Cloud, hybrid and on-premises describe where workloads

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run. You'll use both ideas again in the shared responsibility lesson, because what you must secure

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depends on the service you use. Next, we'll look at the economics of the cloud.