AZ-900: Describe Cloud Concepts

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Describe the benefits and considerations of using cloud services

High Availability







Cloud Agility

Fault Tolerance

Disaster Recovery

Describe the Principles of Economies of Scale

Cloud providers such as Microsoft, Google, and Amazon are large businesses leveraging the benefits of economies of scale. These providers can then pass the savings on to their customers.

Economies of Scale Whitepapers

Describe the differences between:

  • Capital Expenditure (CapEx)
  • Operational Expenditure (OpEx)

Capital Expenditure (CapEx)

Operational Expenditure (OpEx)

Describe the consumption-based model

Capital Expenditure (CapEx) Cost

  • Server Costs
  • Storage Cost
  • Data Center Infrastructure Cost
  • Network Cost
  • Organization Continuity and Disaster
  • Recovery Cost
  • Backup and Archive Cost
  • Technical Personnel

Operational Expenditure (OpEx) Cost

  • Leasing Software and Customization feature cost
  • Scale charge based on usage/demand for fixing hardware and Capacity
  • Billing at the user or the Organization

Comparing Benefits Between Capital Expenditure vs Operational Expenditure

Capital Expenditure

Operational Expenditure

Describe the differences between Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS), and Software-as-a-Service (SaaS)

Infrastructure-as-a-Service (IaaS)

Platform-as-a-Service (PaaS)

PaaS provides an environment for building, testing, and deploying software applications. The goal of PaaS is to help you create an application quickly without managing the underlying infrastructure. For example, when deploying a web application using PaaS, you don’t have to install an operating system, web server, or even system updates.

Software-as-a-Service (SaaS)

SaaS is software that is centrally hosted and managed for the end customer. It is usually based on an architecture where one version of the application is used for all customers, and licensed through a monthly or annual subscription. Microsoft 365, Skype, Gmail, and Dynamics CRM Online are perfect examples of SaaS software.

Cost and Ownership

Comparing IaaS, PaaS and SaaS

Management Resposibilities

Describe the differences between Public, Private, and Hybrid cloud models

Public Cloud


  • High scalability/agility — you don’t have to buy a new server to scale
  • Pay-as-you-go pricing — you pay only for what you use, no CapEx costs
  • You’re not responsible for maintenance or updates of the hardware


  • There may be specific security requirements that cannot be met by using public cloud
  • There may be government policies, industry standards, or legal requirements that public clouds cannot meet
  • You don’t own the hardware or services and cannot manage them as you may want to
  • Unique business requirements, such as having to maintain a legacy application might be hard to meet

Private Cloud


  • You can ensure the configuration can support any scenario or legacy application
  • You have control (and responsibility) over security
  • Private clouds can meet strict security, compliance, or legal requirements


  • You have some initial CapEx costs and must purchase the hardware for startup and maintenance
  • Owning the equipment limits the agility — to scale you must buy, install, and set up new hardware
  • Private clouds require IT skills and expertise that’s hard to come by

Hybrid Cloud


  • You can keep any systems running and accessible that use out-of-date hardware or an out-of-date operating system
  • You have flexibility with what you run locally versus in the cloud
  • You can take advantage of economies of scale from public cloud providers for services and resources where it’s cheaper, and then supplement with your own equipment when it’s not
  • You can use your own equipment to meet security, compliance, or legacy scenarios where you need to completely control the environment


  • It can be more expensive than selecting one deployment model since it involves some CapEx cost upfront
  • It can be more complicated to set up and manage

Check your Knowledge


  • Cloud providers offer service-level agreements (SLAs) that guarantee a certain level of availability, but only for those systems that are controlled by them.
  • Moving to the cloud can help avoid downtime caused by network outages, system outages, and power outages. It can also help you if you need to diagnose problems with an application or problems with an external system that your application uses.
  • You can scale up (or vertically) when you want to add additional CPUs or more memory using a more powerful VM.
  • You can scale out (or horizontally) if you want to add more VMs to handle the additional load.
  • Cloud providers give you ways to automatically scale based on usage patterns, resource utilization, and times of the day. This is referred to as elasticity.
  • Cloud providers monitor the health of the infrastructure. When a VM becomes unhealthy, the cloud provider can automatically move you to a healthy VM without you having to do anything. This is called fault tolerance.
  • Cloud providers also operate across multiple data centers that are in different regions of the world. If a natural disaster (or any other disaster) happens in one region, you can switch over to another region, assuming you have replicated your environment in multiple regions. This kind of planning is called Business Continuity and Disaster Recovery Planning, and cloud providers often have features in place to make implementing a plan easy. This is often referred to as disaster recovery.
  • Because you are using infrastructure owned by the cloud provider, moving to the cloud reduces your capital expenses, the major expenses that are incurred for infrastructure and other major purchases. Cloud providers take advantage of the principle of economies of scale by purchasing large amounts of infrastructure to be used by cloud consumers.
  • Day-to-day expenses (operational expenses) can also be reduced in the cloud because you pay only for those resources you are using at any particular time. This consumption-based model is a key benefit of the cloud.
  • Infrastructure-as-a-Service (IaaS) offers infrastructure running in the cloud, but you have to maintain the operating system and what’s installed on that infrastructure. IaaS services offer you the most control in the cloud, but they also carry the largest management burden.
  • Platform-as-a-Service (PaaS) offloads the management of the infrastructure, and it also offloads the operating system and components installed on the VMs to the cloud provider. You are responsible for your application. PaaS services also offer many additional features that make it easy to add functionality to an application without having to write complex code. Development teams also have a wide variety of deployment methods available, and the cloud provider often automates much of that process.
  • Software-as-a-Service (SaaS) provides a hosted application in the cloud that is most commonly accessed using a web browser. In a SaaS service, the cloud provider manages everything for you. You are essentially renting the use of the software from the cloud provider. A big benefit of SaaS is that it makes applications easily-accessible by employees in the field on any device.
  • The public cloud model is sometimes referred to as a multitenant environment. Multiple companies and users share the same infrastructure. VMs and other infrastructure are allocated to users as they need them, and when they no longer need them, they are returned to the pool to be used by other users. The network is available publicly over the Internet, but you do have the ability to put security methods in place to control access to your resources.
  • The private cloud model is sometimes referred to as a single-tenant environment. All infrastructure is private to an individual or a company, and the network is only available within the private cloud itself. It is not exposed to the Internet. In many cases, the infrastructure used in a private cloud is owned by the company, but not always. It’s possible to host a private cloud in a third-party data center.
  • A hybrid cloud model is a mixture of public and private cloud models. Hybrid clouds are often used when a company needs to use on-premises resources in a cloud application.

More Resources

  1. Cloud Concepts — Principle of Cloud Computing

Module -2

Describe Core Azure Services