Cloud models, characteristics and enabling technologies notes — Unit 1

Cloud computing is the delivery of computing services—including servers, storage, databases, networking, software, analytics, and intelligence—over the Internet ('the cloud') to offer faster innovation, flexible resources, and economies of scale.

⇒1.1 The Shift from On-Premises

Historically, companies had to buy physical servers, rent data center space, power them, cool them, and hire IT staff to maintain them (CapEx - Capital Expenditure). If traffic spiked, the server crashed. If traffic dropped, the expensive server sat idle.

Cloud computing shifts this to OpEx (Operational Expenditure). You rent hardware by the second from a cloud provider (AWS, Azure, GCP) and only pay for exactly what you use.

The National Institute of Standards and Technology (NIST) provides the globally accepted definition of cloud computing, consisting of five essential characteristics, three service models, and four deployment models.

⇒2.1 Five Essential Characteristics

• On-demand self-service: A consumer can unilaterally provision computing capabilities, such as server time and network storage, as needed automatically without requiring human interaction with each service provider.
• Broad network access: Capabilities are available over the network and accessed through standard mechanisms (browsers, mobile phones, thin clients).

• Resource pooling: The provider's computing resources are pooled to serve multiple consumers using a multi-tenant model, with different physical and virtual resources dynamically assigned and reassigned according to consumer demand.
• Rapid elasticity: Capabilities can be elastically provisioned and released, in some cases automatically, to scale rapidly outward and inward commensurate with demand. To the consumer, resources appear to be unlimited.
• Measured service: Cloud systems automatically control and optimize resource use by leveraging a metering capability. Resource usage can be monitored, controlled, and reported, providing transparency for both the provider and consumer.

⇒4.1 Infrastructure as a Service (IaaS)

The most basic category of cloud computing services. With IaaS, you rent IT infrastructure—servers and virtual machines (VMs), storage, networks, operating systems—from a cloud provider on a pay-as-you-go basis.

• What the provider manages: Physical data center, cooling, power, networking hardware, hypervisor, and physical servers.
• What you manage: Operating system, middleware, runtime, data, and applications.
• Examples: Amazon EC2, Google Compute Engine, Microsoft Azure VMs.

IaaS gives you the highest level of flexibility and management control over your IT resources.

⇒5.1 Platform as a Service (PaaS)

PaaS is designed to make it easier for developers to quickly create web or mobile apps, without worrying about setting up or managing the underlying infrastructure of servers, storage, network, and databases.

• What the provider manages: Everything in IaaS, PLUS the Operating System, runtime environments (like Node.js or Python environments), middleware, and database engines.
• What you manage: ONLY your application code and your data.
• Examples: AWS Elastic Beanstalk, Heroku, Google App Engine.

PaaS removes the burden of OS patching and load balancer configuration, allowing developers to focus purely on coding.

⇒6.1 Software as a Service (SaaS)

SaaS is a method for delivering software applications over the Internet, on demand and typically on a subscription basis. Users connect to the application over the Internet, usually with a web browser.

• What the provider manages: Absolutely everything. Physical hardware, OS, runtime, application code, data backups, and security.
• What you manage: Nothing. You just log in and use the software.
• Examples: Gmail, Salesforce, Microsoft 365, Dropbox.

SaaS provides a complete product that is run and managed by the service provider.

Not all clouds are the same, and not one type of cloud computing is right for everyone. Several different deployment models have evolved.

⇒7.1 Public Cloud

Public clouds are owned and operated by a third-party cloud service provider, which delivers their computing resources over the Internet. All hardware, software, and other supporting infrastructure is owned and managed by the cloud provider.

In a public cloud, you share the same hardware, storage, and network devices with other organizations or cloud 'tenants'. Advantages include lower costs (no hardware to buy), no maintenance, and high reliability.

⇒8.1 Private Cloud

A private cloud refers to cloud computing resources used exclusively by a single business or organization. A private cloud can be physically located on the company's on-site datacenter. Some companies also pay third-party service providers to host their private cloud.

The services and infrastructure are maintained on a private network. It offers the same self-service and scalability as a public cloud, but with the control, security, and customization available from dedicated resources. Highly regulated industries (like banking and healthcare) often use private clouds.

⇒9.1 Hybrid Cloud

Hybrid clouds combine public and private clouds, bound together by technology that allows data and applications to be shared between them. By allowing data and applications to move between private and public clouds, a hybrid cloud gives your business greater flexibility (e.g., using public cloud for high-volume, low-security tasks like web serving, and private cloud for sensitive database hosting).

⇒9.2 Community Cloud

The cloud infrastructure is provisioned for exclusive use by a specific community of consumers from organizations that have shared concerns (e.g., mission, security requirements, policy, and compliance considerations). It may be owned, managed, and operated by one or more of the organizations in the community.

Cloud computing is not a single new technology; rather, it is the integration and evolution of several foundational technologies.

⇒10.1 Broadband Networks and Internet Architecture

Without high-speed, reliable, and globally accessible internet connections, centralized computing (like SaaS) would be impossible. Advances in fiber optics, TCP/IP routing algorithms, and content delivery networks (CDNs) ensure that accessing a server 5,000 miles away feels instantaneous.

Virtualisation is the absolute core enabling technology of cloud computing. It is the process of creating a software-based (or virtual) representation of something rather than a physical one.

⇒11.1 The Hypervisor

A hypervisor is software that sits on top of physical hardware and allows multiple operating systems to run alongside each other, sharing the same physical computing resources (CPU, RAM). It tricks each OS into thinking it has its own dedicated physical machine.

This enables 'Resource Pooling' and 'Multi-tenancy'. A cloud provider can buy one massive physical server and rent out 50 isolated Virtual Machines on it to 50 different customers.

⇒12.1 Web Services (APIs)

Cloud computing heavily relies on Service-Oriented Architecture (SOA) and RESTful APIs. When a developer wants to spin up a new server on AWS, they do not email an administrator. Their code sends an HTTP POST request to an AWS API endpoint, and the server is provisioned automatically. Everything in the cloud is API-driven.

⇒12.2 Web 2.0 and AJAX

The evolution of web browsers to support complex JavaScript execution (AJAX, React) allowed rich, desktop-like user interfaces (like Google Docs or the AWS Management Console) to exist within a browser, eliminating the need for installed client software.

A cloud is essentially a massive distributed system. Thousands of commodity servers are networked together to act as a single, incredibly powerful machine.

⇒13.1 Distributed File Systems

Technologies like the Google File System (GFS) or Hadoop Distributed File System (HDFS) allow data to be striped and replicated across thousands of physical hard drives. If a hard drive or an entire server rack fails, the data is not lost because copies exist on other servers. This provides the 'Availability' and 'Elasticity' characteristics.

⇒14.1 Utility Computing

Utility computing is the packaging of computing resources as a metered service. Just like electricity or water, you pay for exactly what you consume. This requires complex backend monitoring systems.

⇒14.2 Challenges

• Security and Privacy: Moving data to third-party servers raises compliance, data sovereignty, and breach concerns.
• Vendor Lock-in: Building heavily on proprietary APIs (like DynamoDB) makes moving to another provider costly.
• Latency and Outages: Cloud architectures are subject to network latency constraints and massive regional outages outside the customer's control.