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CS-802 (B) · Cloud Computing/Quick Revision Short Notes

Cloud Computing (CS-802 (B)) - Unit 2 Short Notes

How unit 2 is examined

Covers metered and elastic computing, Ajax and mashups, virtualization with its pitfalls, and multitenant software; virtualization services, pitfalls, mashups and multitenancy risks carry the marks.

Utility Computing

<span style="display:inline-block;padding:.16em .6em;border:1.5px solid currentColor;border-radius:999px;font-size:.68em;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.75">Low weight</span>

Definition. <mark>Utility computing is a service model in which computing resources such as processing, storage and software are provided on demand and billed by metered usage, like electricity or water.</mark>

Key points.

  1. The customer owns no infrastructure and pays only for what is consumed, so capital expense becomes operating expense.
  2. Resources are provisioned by the provider and metered per unit, for example CPU-hours, GB stored or GB transferred.
  3. Cloud IaaS such as Amazon EC2 is the modern form of utility computing.

Utility vs Elastic computing.

Basis Utility computing Elastic computing
Concept Metered, pay-per-use billing model Ability to grow and shrink resources automatically with load
Provisioning Provider supplies resources on request System adds or removes resources without manual action
Pricing Charged by usage (CPU-hours, GB) Charged for the capacity actually running at that time
Scalability Not necessarily automatic Automatic, in both directions
Example Paying per hour for a VM Auto-scaling group adding servers on a sale day

Grid vs Utility computing.

Basis Grid computing Utility computing
Purpose Pool many organisations' machines to solve one large scientific task Supply computing as a service to any paying customer
Resource sharing Voluntary, distributed, heterogeneous nodes Centrally owned by a provider and rented out
Business model Collaboration, mostly non-commercial Commercial pay-per-use
Example SETI@home, CERN grid AWS, Azure

Asked: [7 marks] (May 2022) Differentiate between Utility computing and Elastic computing. Asked: [7 marks] (Dec 2024) Give difference between Grid computing and utility computing.

Elastic Computing

<span style="display:inline-block;padding:.16em .6em;border:1.5px solid currentColor;border-radius:999px;font-size:.68em;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.75">Low weight</span>

Definition. <mark>Elastic computing is the ability of a cloud to automatically provision and release resources as demand rises and falls, so capacity always matches load.</mark>

Key points.

  1. Scalability is the ability to handle growth, whereas elasticity is doing so automatically and in both directions, including scaling back in.
  2. Its characteristics are on-demand scaling, automatic provisioning and pay-per-use billing.
  3. It removes both over-provisioning (idle cost) and under-provisioning (lost customers).
  4. Example: an e-commerce site auto-scales servers during a festival sale and shrinks afterwards.
Basis Traditional computing Elastic cloud computing
Capacity Fixed, sized for peak load Varies automatically with demand
Cost Large upfront purchase, idle at off-peak Pay only for used capacity
Scaling Manual, takes weeks to buy hardware Automatic, in minutes
Management Own staff maintain hardware Provider manages infrastructure
Example In-house server for a shop Shop on AWS auto-scaling

Asked: [7 marks] (May 2026) Explain elastic computing. Differentiate between traditional computing systems and elastic cloud computing systems with example.

Ajax: asynchronous rich interfaces

<span style="display:inline-block;padding:.16em .6em;border:1.5px solid currentColor;border-radius:999px;font-size:.68em;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.75">Low weight</span>

Definition. <mark>Ajax (Asynchronous JavaScript and XML) is a technique that lets a web page exchange data with the server in the background and update only part of the page, without a full reload.</mark>

Key points.

  1. In synchronous communication the client sends a request and blocks until the reply arrives; in asynchronous communication it continues working and a callback handles the reply when it comes.
  2. The browser's Ajax engine, a JavaScript layer using the XMLHttpRequest object, sends requests on behalf of the page and receives the responses.
  3. Non-blocking interaction means the user keeps typing or scrolling while data loads, unlike polling, which repeatedly asks the server whether anything changed.
  4. Only the changed data (XML or JSON) travels, and the DOM is updated in place (partial page update), which saves bandwidth and feels fast.
  5. Role: Ajax gives desktop-like rich interfaces such as Google Maps panning, Gmail loading mail, and live search suggestions.

Asked: [7 marks] (May 2026) Describe the working principles of asynchronous communication and explain the role of Ajax in interactive web application environments.

Mashups: User interface

<span style="display:inline-block;padding:.16em .6em;border:1.5px solid currentColor;border-radius:999px;font-size:.68em;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.75">Medium weight</span>

Definition. <mark>A cloud mashup is a web application that combines data, functions or content from two or more cloud services or APIs into one new integrated service with a single user interface.</mark>

Key points.

  1. Need: mashups integrate existing services quickly, so new applications are built by reuse instead of from scratch, which gives agility and lower cost.
  2. The user interface layer shows the combined result through widgets, portals and pages, and Ajax keeps it responsive by refreshing parts without a reload.
  3. Architecture has three layers: content providers (APIs, RSS, web services), the mashup server that fetches and merges data, and the client browser interface.
  4. Types include consumer mashups (maps with photos), data mashups (merging feeds) and enterprise mashups (combining internal and external data).
  5. Example workflow: fetch property listings from one API, plot them using the Google Maps API, and show them on one page.
  6. Benefits are speed and reuse; challenges are dependence on third-party APIs, security of shared data and inconsistent data formats.
  7. VMware machine imaging: a machine image is a saved template of a VM (OS, applications, settings); VMware vSphere creates, stores and clones such images so identical VMs are deployed in minutes and consistently.

Answer frame. Open with the mashup definition; draw the three-layer diagram (providers, mashup server, browser UI); develop points 1-6; close with one benefit and one challenge. For the Dec 2024 part ii, define machine image, then vSphere cloning and benefits.

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Asked: [7 marks] (May 2023) Discuss in detail cloud Mashups with User interface. Asked: [7 marks] (Dec 2024) i) Why is there need of cloud Mashups in cloud computing? ii) Explain VMware and VSphere machine imaging.

Services Virtualization Technology

<span style="display:inline-block;padding:.16em .6em;border:1.5px solid currentColor;border-radius:999px;font-size:.68em;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.75">High weight</span>

Definition. <mark>Virtualization is the technique of abstracting physical hardware using a hypervisor so that many isolated virtual machines, each with its own OS, run on one physical machine.</mark>

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Key points.

  1. Virtualization services cover server, storage, network, desktop and application virtualization; each turns a physical resource into a logical pool that can be allocated on demand.
  2. Server virtualization splits one server into many VMs; storage virtualization pools disks into one logical store; network virtualization creates virtual switches and VLANs.
  3. The hypervisor is Type 1 (bare-metal, e.g. Xen, ESXi) running directly on hardware, or Type 2 (hosted, e.g. VirtualBox) running on a host OS.
  4. Hardware virtualization techniques: full virtualization emulates complete hardware so the guest OS is unmodified; paravirtualization modifies the guest OS to call the hypervisor for better performance; hardware-assisted virtualization uses CPU support (Intel VT-x, AMD-V).
  5. VMs are suggested because they give isolation, several OSes on one machine, high hardware utilization, flexible resource allocation and easy maintenance.
  6. A virtual cluster is a pool of VMs that behaves as one computing cluster, giving fault tolerance through VM migration and cost saving through less hardware and power.
  7. Benefits: better utilization, lower cost, scalability, security through isolation, dynamic allocation, live migration, snapshots and disaster recovery.
  8. Fast VM cloning needs a hypervisor with snapshot and clone functions, copy-on-write disk images, and shared storage so a clone shares unchanged blocks and copies only changes.
  9. Fast recovery: a healthy VM is cloned or a snapshot is restored in minutes, which cuts the recovery time objective and prevents data loss.

Answer frame. Open with the definition; draw the hypervisor diagram; for "services", develop points 1-2 and 7; for "why VMs and clusters", points 3, 5, 6, 7; for "techniques", point 4 then 7; for cloning, points 8-9. Close with the sentence that virtualization is the foundation of cloud computing.

Asked: [7 marks] (May 2023) What are the services provided by Virtualization explain in detail? Asked: [7 marks] (May 2024, Jun 2025) Why are virtual machine and virtual clusters suggested in cloud computing system? / What is virtualization technology? How is it used in cloud environments? Asked: [? marks] (May 2024) What virtualization support is needed to achieve fast cloning of VMs? Explain how VM cloning can enable fast recovery. Asked: [? marks] (May 2024) What are hardware virtualization techniques? What are the benefits of virtualization.

Virtualization applications in enterprises

<span style="display:inline-block;padding:.16em .6em;border:1.5px solid currentColor;border-radius:999px;font-size:.68em;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.75">Not asked since 2022</span>

Definition. Enterprise virtualization applies VMs, virtual storage and virtual networks inside a company to run its workloads on fewer physical machines.

Key points.

  1. Server consolidation runs many lightly used servers as VMs on a few hosts, cutting hardware, power and space cost.
  2. Test and development environments are created and destroyed in minutes using VM templates.
  3. Disaster recovery and business continuity use VM snapshots and live migration to restart services on another host.
  4. Virtual desktop infrastructure (VDI) serves employees a managed desktop from the data center.

Pitfalls of virtualization

<span style="display:inline-block;padding:.16em .6em;border:1.5px solid currentColor;border-radius:999px;font-size:.68em;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.75">Medium weight</span>

Definition. <mark>Virtualization pitfalls are the risks and drawbacks that appear when many VMs share one physical host, such as security exposure, overhead and management complexity.</mark>

Key points.

  1. Security risk: a compromised hypervisor or a VM escape exposes every VM on the host, and VM-to-VM attacks become possible.
  2. Performance overhead: the hypervisor layer consumes CPU and memory, and I/O-heavy applications run slower than on bare metal.
  3. Single point of failure: if the physical host fails, all VMs on it go down together.
  4. Licensing complexity: software licensed per CPU or per machine becomes costly or unclear when VMs are copied or moved.
  5. VM sprawl: VMs are so easy to create that unused ones accumulate, wasting resources and complicating management.
  6. Management and network complexity: monitoring, patching and networking hundreds of VMs needs special tools and skills.
  7. Mitigation: harden and patch the hypervisor, isolate networks, use clustering with live migration for failover, and track VM lifecycle and licences.

Answer frame. Open with the definition; no diagram needed; develop points 1-6 in order of severity; close with point 7 as the mitigation and note that benefits still outweigh the pitfalls when managed.

Asked: [7 marks] (May 2022, Dec 2024) Discuss the pitfalls of virtualization. / What are the challenges of virtualization in cloud computing?

Multitenant software: Multi-entity support

<span style="display:inline-block;padding:.16em .6em;border:1.5px solid currentColor;border-radius:999px;font-size:.68em;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.75">Medium weight</span>

Definition. <mark>Multitenant software is a single instance of an application that serves many customers (tenants) at once, each seeing only its own isolated data and customised configuration.</mark>

Key points.

  1. In SaaS a shared application and database serve all tenants; in PaaS the shared platform runs tenant apps; in IaaS tenants share physical hosts through VMs.
  2. Multitenant techniques are logical isolation of each tenant's data, sharing of resources for low cost, and per-tenant customisation of settings and branding.
  3. Risk of data isolation failure: a coding or access-control bug can let one tenant read another's data.
  4. Noisy neighbour: one tenant's heavy load slows the shared resources of others.
  5. Side-channel attacks: a malicious co-resident VM can infer secrets through shared caches or timing.
  6. Across environments the risk is highest in a public cloud with unknown neighbours, lower in a private cloud owned by one organisation, and in between in a hybrid cloud, where the link also needs protection.
  7. Mitigations: strong isolation, encryption of data at rest and in transit, access control, and SLA terms with quotas.
  8. A virtualized data center pools resources, manages VMs and provisions them automatically; load balancing spreads requests over servers and resource optimization uses CPU, memory and storage efficiently to cut cost.

Answer frame. Open with the multitenancy definition; develop points 1, 3, 4, 5, then 6 as a public/private/hybrid comparison; close with point 7. For short notes, pick any two of point 2 and point 8 and write three lines each.

Asked: [7 marks] (May 2023) Explain the risk from Multi-tenancy with respect to various cloud Environment. Asked: [? marks] (May 2024) Write short notes on following (any two): a) Virtualized data center b) Multitenant techniques c) Load balancing and Resource optimization Asked: [7 marks] (Dec 2024) What is multitenant software? (part ii of the grid vs utility question)

Multi-schema approach

<span style="display:inline-block;padding:.16em .6em;border:1.5px solid currentColor;border-radius:999px;font-size:.68em;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.75">Low weight</span>

Definition. <mark>The multi-schema approach gives each tenant its own schema (its own set of tables) inside one shared database instance.</mark>

Key points.

  1. Separate schema: every tenant has its own tables, which gives strong isolation, easy per-tenant customisation and simple backup or restore.
  2. Shared schema: all tenants share the same tables with a tenant-ID column, which is cheapest and scales to many tenants but isolates weakly.
  3. Trade-off: more schemas mean more management and less scalability, while fewer schemas mean lower cost but harder customisation.
  4. Examples are Salesforce (shared, metadata-driven) and SaaS products on PostgreSQL or Oracle using one schema per tenant.

Asked: [7 marks] (Jun 2025) Explain the multi-schema approach in cloud databases.

Multi-tenancy using cloud data stores

<span style="display:inline-block;padding:.16em .6em;border:1.5px solid currentColor;border-radius:999px;font-size:.68em;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.75">Not asked since 2022</span>

Definition. Multi-tenancy on cloud data stores means many tenants keep data in a shared non-relational store such as Bigtable, SimpleDB or DynamoDB.

Key points.

  1. These stores have no fixed schema, so each tenant's records can carry different attributes.
  2. A tenant ID is placed in the row key or partition key so each tenant's data is stored and queried separately.
  3. They scale horizontally across many servers, which suits many small tenants.
  4. Access control and per-tenant quotas must be enforced by the application layer, since the store has weaker built-in isolation.

Last-minute revision

  • Utility computing: metered pay-per-use, like electricity; elastic computing: automatic scale-out and scale-in.
  • Scalability handles growth; elasticity does it automatically both ways.
  • Ajax = asynchronous requests via XMLHttpRequest with partial page update, no full reload.
  • Mashup = combination of two or more services/APIs in one UI; layers are providers, mashup server, browser.
  • Virtualization services: server, storage, network, desktop, application.
  • Type 1 hypervisor is bare-metal; Type 2 is hosted.
  • Techniques: full, paravirtualization, hardware-assisted (VT-x, AMD-V).
  • Fast cloning needs snapshots plus copy-on-write; recovery time falls.
  • Pitfalls: security, overhead, single point of failure, licensing, VM sprawl, complexity.
  • Multitenancy risks: isolation failure, noisy neighbour, side channels.
  • Multi-schema: separate schema per tenant (isolated) versus shared schema with tenant ID (cheap).

Memory hooks

  • Utility = meter; Elastic = rubber band.
  • Ajax: "ask in the background, change one part".
  • Mashup layers: Provider, Server, Screen (PSS).
  • Pitfalls: "SO-SLIM" security, overhead, SPOF, licensing, individual sprawl, management.
  • Tenant risks: I-N-S (isolation, noisy, side channel).

Coverage checklist

  • Utility Computing: Q10 (Utility vs Elastic), Q11 part i (Grid vs Utility).
  • Elastic Computing: Q2.
  • Ajax: asynchronous 'rich' interfaces: Q1.
  • Mashups: User interface: Q3, Q4.
  • Services Virtualization Technology: Q8, Q9, Q13, Q14.
  • Virtualization applications in enterprises: no past questions.
  • Pitfalls of virtualization: Q7.
  • Multitenant software: Multi-entity support: Q6, Q12, Q11 part ii.
  • Multi-schema approach: Q5.
  • Multi-tenancy using cloud data stores: no past questions.
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