Cloud computing is the on-demand delivery of IT resources — such as servers, storage, databases, networking, software, and analytics — over the internet (the cloud). Instead of buying, owning, and maintaining physical data centres, you can access these resources on a pay-as-you-go basis from providers like AWS, Azure, or Google Cloud.

Key benefits: Cost savings, scalability, flexibility, and faster time to market.

IaaS (Infrastructure as a Service): Provides virtualised computing resources over the internet. You manage the OS, applications, and data. Example: AWS EC2, Google Compute Engine.

PaaS (Platform as a Service): Provides a platform to develop, run, and manage applications without managing the underlying infrastructure. Example: AWS Elastic Beanstalk, Google App Engine.

SaaS (Software as a Service): Delivers software applications over the internet, fully managed by the provider. Example: Google Workspace, Salesforce.

Public Cloud: Services are delivered over the public internet and shared across multiple organisations. Examples: AWS, Azure, GCP.

Private Cloud: Services are dedicated to a single organisation, either on-premises or hosted by a third party. Offers greater control and security.

Hybrid Cloud: Combines public and private clouds, allowing data and applications to be shared between them. Offers flexibility and scalability while keeping sensitive data secure.

Amazon Elastic Compute Cloud (EC2) is a web service that provides resizable compute capacity in the cloud. It allows you to launch virtual servers (instances) with various operating systems and configurations.

Key features:

• Scalable — scale up or down based on demand
• Pay-as-you-go pricing
• Multiple instance types (general, compute, memory, storage)
• Integration with other AWS services
• Auto-scaling and load balancing

Amazon Simple Storage Service (S3) is an object storage service that offers industry-leading scalability, data availability, and security. It's used for storing and retrieving any amount of data from anywhere.

How data is stored:

• Data is stored as objects in buckets.
• Each object has a key (name), value (data), and metadata.
• Buckets are globally unique and stored in a specific region.
• Supports versioning, lifecycle policies, and encryption.

The Shared Responsibility Model defines what the cloud provider is responsible for and what the customer is responsible for.

Cloud Provider (AWS/Azure/GCP):

• Security of the cloud (physical infrastructure, hardware, software, networking)
• Managed services (e.g., S3, RDS, Lambda)

Customer (You):

• Security in the cloud (data, applications, access management)
• Configuration, patching, and IAM

Key takeaway: You are responsible for securing your data and applications, while the provider secures the underlying infrastructure.

A disaster recovery strategy ensures business continuity in case of failures. Here's a high-level approach:

• Identify critical applications and define Recovery Time Objective (RTO) and Recovery Point Objective (RPO).
• Use multiple regions — replicate data and applications across geographically separated regions.
• Automate failover using services like AWS Route 53, Azure Traffic Manager, or GCP Cloud DNS.
• Implement regular backups using services like AWS Backup, Azure Backup, or GCP Backup and DR.
• Test your DR plan regularly to ensure it works as expected.

Vertical Scaling (Scale Up): Adding more power (CPU, RAM) to an existing server. Example: Upgrading an EC2 instance to a larger size.

• Pros: Simple, no architecture changes needed.
• Cons: Limited by hardware, single point of failure.

Horizontal Scaling (Scale Out): Adding more servers to handle increased load. Example: Adding more EC2 instances behind a load balancer.

• Pros: Better fault tolerance, unlimited scaling potential.
• Cons: More complex, requires distributed architecture.

Migrating to the cloud requires careful planning. Key considerations include:

• Assessment: Evaluate current infrastructure, dependencies, and performance.
• Migration Strategy: Choose between rehost (lift and shift), replatform, refactor, or rebuild.
• Security: Implement IAM, encryption, and compliance controls.
• Cost Management: Understand pricing models and optimise for cost.
• Data Migration: Plan for data transfer, backup, and validation.
• Testing: Thoroughly test the migrated application before going live.

The main cloud service providers are Amazon Web Services (AWS), Microsoft Azure, and Google Cloud Platform (GCP). Other notable providers include IBM Cloud and Oracle Cloud.

IaaS provides virtualised computing resources (servers, storage, networking) that you manage. PaaS provides a platform for developing and running applications without managing the underlying infrastructure.

A cloud region is a specific geographic location where cloud providers have data centres. Each region is isolated from others for fault tolerance and compliance.

It defines what the cloud provider is responsible for (security of the cloud) and what the customer is responsible for (security in the cloud, including data, applications, and access management).

For beginners, the AWS Certified Cloud Practitioner, Azure Fundamentals, or Google Cloud Digital Leader are great starting points. Then, move to associate-level certifications like AWS Solutions Architect or Azure Administrator.