Question 1

Explain IaaS, PaaS, and SaaS with examples.

Accepted Answer

These are the three main models of cloud computing services:

1.  **IaaS (Infrastructure as a Service)**: Provides virtualized computing resources over the internet. You manage the OS, runtime, and data.
    *   *Examples*: AWS EC2, Google Compute Engine, DigitalOcean.
2.  **PaaS (Platform as a Service)**: Provides a platform allowing customers to develop, run, and manage applications without the complexity of building and maintaining the infrastructure. You manage data and the application.
    *   *Examples*: Google App Engine, Heroku, AWS Elastic Beanstalk.
3.  **SaaS (Software as a Service)**: Provides software usage over the internet. You just use it.
    *   *Examples*: Gmail, Salesforce, Dropbox, Zoom.

Question 2

Scalability vs Elasticity - What is the difference?

Accepted Answer

While related, they refer to different aspects of resource management:

### Scalability
The ability of a system to handle increased load by adding resources.
*   **Vertical Scaling (Scale Up)**: Adding more power (CPU, RAM) to an existing server.
*   **Horizontal Scaling (Scale Out)**: Adding more servers to a pool.
*   *Key*: Usually a planned, long-term strategic decision.

### Elasticity
The ability to **automatically** add or remove resources to match the current demand in real-time.
*   *Key*: Fits perfectly with the "Pay-as-you-go" cloud model. Handles spikes dynamically.

Question 3

Public vs Private vs Hybrid Cloud

Accepted Answer

*   **Public Cloud**: Services are delivered over the public internet and shared across an organization.
    *   *Pros*: Cost-effective, high reliability, no maintenance.
    *   *Example*: AWS, Azure.
*   **Private Cloud**: Cloud computing resources used exclusively by a single business or organization. Can be physically located at the company's on-site datacenter or hosted by a third-party.
    *   *Pros*: More security and control.
    *   *Cons*: High cost.
*   **Hybrid Cloud**: Combines public and private clouds, bound together by technology that allows data and applications to be shared between them.
    *   *Pros*: Flexibility, policy-based control (keep sensitive data private, burst to public for heavy load).

Question 4

What is CAP Theorem in distributed systems?

Accepted Answer

The **CAP Theorem** states that a distributed data store can effectively provide only **two** of the following three guarantees:

1.  **Consistency (C)**: Every read receives the most recent write or an error.
2.  **Availability (A)**: Every request receives a (non-error) response, without the guarantee that it contains the most recent write.
3.  **Partition Tolerance (P)**: The system continues to operate despite an arbitrary number of messages being dropped or delayed by the network between nodes.

**Note**: In a distributed system, partition tolerance (P) is mandatory. So you must trade-off between C and A (CP vs AP).

Question 5

What is a CDN and how does it improve performance?

Accepted Answer

A **Content Delivery Network (CDN)** is a geographically distributed group of servers which work together to provide fast delivery of Internet content.

### How it works:
*   It caches content (like images, videos, CSS) in "Edge Servers" located close to end-users.
*   When a user requests content, it loads from the nearest Edge Server instead of the origin server.

### Benefits:
*   Reduced Latency.
*   Lower Bandwidth costs.
*   Improved security (DDoS protection).

Question 6

Virtual Machines (VM) vs Containers (Docker)?

Accepted Answer

### Virtual Machines
*   Virtualize the **Hardware**.
*   Each VM runs a full Operating System (Guest OS).
*   **Heavy**: Slow boot times, high memory usage.
*   **Isolation**: Complete isolation (more secure).

### Containers
*   Virtualize the **Operating System** (Kernel).
*   Share the Host OS kernel.
*   **Lightweight**: Start in milliseconds, very low overhead.
*   **Portable**: "Write once, run anywhere".

Question 7

What is Load Balancing and what algorithm does it use?

Accepted Answer

**Load Balancing** refers to distributing incoming network traffic across a group of backend servers (Server Farm).

### Purpose:
*   Prevents any single server from becoming a bottleneck.
*   Increases availability and reliability.

### Algorithms:
1.  **Round Robin**: Requests are distributed sequentially.
2.  **Least Connections**: Sends requests to the server with the fewest active connections.
3.  **IP Hash**: Uses the client's IP address to determine which server receives the request.

Question 8

What is Serverless Computing?

Accepted Answer

**Serverless Computing** is a cloud execution model where the cloud provider dynamically manages the allocation of machine resources. Pricing is based on the actual amount of resources consumed by an application, rather than on pre-purchased units of capacity.

*   You write code (functions) and upload them (e.g., AWS Lambda).
*   **Event-driven**: Only runs when triggered (HTTP request, database change).
*   **No Ops**: No server patching or management.

Question 9

What are Regions and Availability Zones (AZs)?

Accepted Answer

### Region
A separate geographic area (e.g., "us-east-1" in N. Virginia). Each region creates a completely independent fault domain.

### Availability Zone (AZ)
Within a Region, there are multiple isolated locations known as Availability Zones.
*   An AZ consists of one or more discrete data centers with redundant power, networking, and connectivity.
*   **Best Practice**: Deploy applications across multiple AZs to ensure high availability and fault tolerance.

Question 10

What is Object Storage (e.g., AWS S3)?

Accepted Answer

**Object Storage** is a data storage architecture that manages data as objects, as opposed to file hierarchies (File Storage) or blocks (Block Storage).

### Characteristics:
*   **Flat Structure**: No folders, just buckets and keys.
*   **Metadata**: Each object has data, variable amounts of metadata, and a global unique identifier.
*   **Scalability**: Extremely scalable storage for unstructured data (images, backups, logs).
*   Accessed via HTTP API.

Cloud Computing Essentials

1Explain IaaS, PaaS, and SaaS with examples.

2Scalability vs Elasticity - What is the difference?

3Public vs Private vs Hybrid Cloud

4What is CAP Theorem in distributed systems?

5What is a CDN and how does it improve performance?

6Virtual Machines (VM) vs Containers (Docker)?

7What is Load Balancing and what algorithm does it use?

8What is Serverless Computing?

9What are Regions and Availability Zones (AZs)?

10What is Object Storage (e.g., AWS S3)?