When you scroll through Instagram, stream your favorite show on Netflix, or shop on Amazon, you probably don’t pause to think about what’s happening behind the scenes.

But with every tap, click, or refresh, a complex network of interconnected components work seamlessly to deliver a smooth experience.

At the core of this seamless experience lies system design—the process of defining the architecture, components, modules, interfaces, and data to meet specific functional and non-functional requirements.

Think of system design like an architect designing a skyscraper. They don't just start laying bricks.

First, they gather requirements:

• How many floors will it have?
• How many people should it support?
• What type of soil is it built on?
• What level of earthquake resistance is needed?

Once the requirements are clear, the architect creates detailed blueprints that describe the foundation, structural supports, electrical systems, plumbing, and elevator shafts.

These correspond to the system's components, modules, and interfaces. They also consider how different systems interact, such as how plumbing might affect electrical layouts.

They plan for future expansion (scalability) and think about how the building will handle unexpected issues (fault tolerance).

In the software world, this translates to:

• Architecture: The overall structure of the system. Should it be built as a monolith, a set of microservices, or an event-driven system?
• Components/Modules: Databases, servers, load balancers, caches, message queues, and APIs.
• Interfaces: How these components communicate with each other (e.g., REST APIs, gRPC).
• Data: How data is stored, managed, accessed, and kept consistent.

System Design is not about writing code (initially). It's about making high-level decisions and trade-offs before a single line of code is written.

1. 10 Big Questions of System Design

On a high level, system design revolves around answering these 10 big questions:

1. Scalability: How will the system handle a large number of users or requests simultaneously?
2. Latency and Performance: How can we reduce response time and ensure low-latency performance under load?
3. Communication: How do different components of the system interact with each other?
4. Data Management: How should we store, retrieve, and manage data efficiently?
5. Fault Tolerance and Reliability: What happens if a part of the system crashes or becomes unreachable?
6. Security: How do we protect the system against threats such as unauthorized access, data breaches, or denial-of-service attacks?
7. Maintainability and Extensibility: How easy is it to maintain, monitor, debug, and evolve the system over time?
8. Cost Efficiency: How can we balance performance with infrastructure cost?
9. Observability and Monitoring: How do we monitor system health and diagnose issues in production?
10. Compliance and Privacy: Are we complying with relevant laws and regulations (e.g., GDPR, HIPAA)?

2. Key Components of a System

A typical software system can be broken down into several key components:

• Client/Frontend: The part of the system that users interact with directly (e.g., web browsers, mobile apps). It is responsible for displaying information, collecting user input, and communicating with the backend.
• Server/Backend: The backend handles the core functionality of the system. It processes incoming requests, executes business logic, interacts with databases or services, and sends responses back to the client.
• Database/Storage: This component is responsible for storing and managing data. It can take various forms, including relational databases (SQL), non-relational stores (NoSQL), in-memory caches, or distributed object storage systems, depending on the needs of the application.
• Networking Layer: This includes components like load balancers, APIs, and communication protocols that ensure reliable and efficient interaction between different parts of the system.
• Third-party Services: These are external APIs or platforms that extend the system’s capabilities. Common examples include payment processors, email or SMS notification services, authentication providers, analytics tools, and cloud-based AI services.

3. The Process of System Design

Designing a system is not a one-size-fits-all approach. It’s a step-by-step process that starts with understanding the requirements and ends with a detailed blueprint.

Here are the key steps:

Step 1: Requirements Gathering

• Understand what the system needs to do (functional requirements) and how it should behave (non-functional requirements)?
• Who are the users? How many? What are their key actions?
• What is the expected scale (data, traffic)?
• What are the latency, availability, and consistency needs?
• Are there any constraints (e.g., specific technology, budget)?

Step 2: Back-of-the-Envelope Estimation

• Estimate storage, bandwidth, QPS (Queries Per Second), number of servers needed.
• This helps in choosing technologies and designing for scale.

Step 3: High-Level Design (HLD)

• Sketch out the main components of the system and how they interact.
• This is where you decide on major modules, data flows, and external dependencies.

Step 4: Data Model / API Design

• Choose the type of database(s).
• Define schemas, tables, fields, relationships.
• Define the APIs between components (e.g., POST /tweet, GET /timeline).

Step 5: Detailed Design / Deep Dive

• Flesh out each component.
• Discuss scaling strategies for each part.
• Address non-functional requirements (NFRs): How will you achieve availability, reliability, low latency?

Step 6: Identify Bottlenecks and Trade-offs

• Where might the system break under load?
• What are the single points of failure?
• Discuss the pros and cons of your choices (e.g., choosing eventual consistency for higher availability). Every design has trade-offs.

Step 7: Identify Bottlenecks and Trade-offs

• Explain your design decisions.
• Be open to feedback and iterate on the design.

4. Conclusion

System design is a critical skill for building reliable, scalable, and maintainable software systems. Whether you're creating a small application or a large distributed platform, understanding the principles of system design helps you make informed decisions about architecture, technology choices, and performance optimization.

By breaking down the system into key components, following a structured design process, and considering important aspects like scalability and security, you can create systems that not only work efficiently today but are also prepared for the challenges of tomorrow.

Remember, like any craft, system design improves with practice. Start with simple systems, learn from each experience, and gradually tackle more complex systems as your confidence grows.