System Design

System design is the process of designing the architecture and components of a software system
to meet specific business requirements.

• Involves translating user requirements into a detailed blueprint that guides the
implementation phase.

• The goal is to create a well-organized and efficient structure that meets the intended
purpose while considering factors like scalability, maintainability, and performance.

System Design in SDLC

• In SDLC (Software development Life Cycle), without the designing phase, one cannot
jump to the implementation or the testing part.

• System Design is a vital step and also provides the backbone to handle exceptional
scenarios because it represents the business logic of the software.

System Design can be divided into two complementary parts

High-Level Design
It lays out the overall architecture of the system — how major components interact, what services
or modules will exist, and how data flows among them.

• Gives you the big picture: how the system fits together, its core structure, and major
decisions.
 • Done by architects, stakeholders and managers

Prerequisite Technical Knowledge for High Level Design

• Basic Coding Skills (Data Structures and Algorithms)

• Compared to Low Level Design, High Level Design is typically done by more senior people
who have hands-on experience on software projects.

• Knowing the roles of components like databases (SQL and NoSQL), caches and APIs.

• Low Level Design (Object Oriented Programming and Design Patterns)

• In-depth understanding of Functional Requirements (What the system must do e.g., user
registration, streaming) and Non-Functional Requirements (How the system should
perform—scalability, latency, availability, security, etc)

• Networking and Security Fundamentals like DNS, TLS/SSL, rate-limiting, API security, and
basic DDOS protection

• Message queues and streaming tools.

• Knowledge of Microservices vs. Monoliths (When to split services and how to manage
dependencies), fault tolerance, fallback strategies, redundancy, Load Balancer Types &
Algorithms.

• Observability tools Logstash and Alerting systems.

High level Design Includes

• System architecture overview: Defines the major components, modules, and how they
interact (e.g., services, queues, databases)

• Data flow and component interaction: Illustrates how data moves between modules,
along with key integrations and interfaces

• Technology stack and infrastructure: High-level decisions on frameworks, platforms,

hardware, databases, and hosting setups

• Module responsibilities: Describes what each module does and how they relate to one
another

• Performance & trade-offs: Includes design trade-offs, performance considerations,

scalability, security, cost, and other non-functional factors

• Artifacts: Commonly includes architecture diagrams, component and deployment

diagrams, data flow diagrams, and possibly ER/DB schematic overviews.

Real World Examples of High level Design Decisions

• Netflix transitioned their entire backend from a monolith to microservices (starting with
encoding and UI services), completing the migration by 2011 to scale rapidly during high-
load events like holiday seasons.
 • Uber adopted an event-driven architecture where ride requests, location updates, and
fare changes emit events that trigger real-time systems like driver matching, billing, and
dynamic pricing.

• Twitter deployed a load-balanced architecture with caching of trending topics and tweets
to quickly serve millions of users and handle real-time data flows efficiently.

Low-Level Design (Object Oriented Programming and Design Patterns)

It covers how each part works & is implemented internally

• Gives developers a clear, actionable blueprint to build each component.

• Once a High-Level Design is built by stakeholders, it is the job of senior developers and
designers to create a low level design.

Prerequisites / What You Should Know First:

• Basic Coding Skills (Data Structures and Algorithms)

• Strong grasp of OOP concepts (Encapsulation, inheritance, polymorphism & abstraction)

Low Level Design Includes:

• Component/module breakdown: Detailed internal logic for each module—with class
responsibilities, methods, attributes, interactions

• Database schema & structure: Designing tables, keys, indexes, relationships with
SQL/NoSQL refinements

• API & interface definitions: Precise request/response formats, error codes, methods,
endpoints, and internal interfacing

• Error handling & validation logic: Define how each module manages invalid inputs,
failures, edge cases, and logging

• Design patterns & SOLID: Implement design patterns and solid principles to ensure
clean, extensible, maintainable code

• UML and pseudocode artifacts: Class diagrams, sequence diagrams, pseudocode or

flowcharts to clarify logic paths and method calls

Steps for System Design

Here are some steps to get started with system design:

 1. Understand the requirements:

• Before you begin designing the system, you need to understand the requirements.
This involves talking to stakeholders and users, reviewing existing documentation,
and analyzing the business processes that the system will support.

2. Define the system architecture:

• Once you have a clear understanding of the requirements, you can begin defining
the system architecture. This involves identifying the major components of the
system and the interfaces between them.

3. Choose the technology stack:

• Based on the requirements and the system architecture, you can select the
technology stack. This includes choosing the programming language, database,
frameworks, and libraries that will be used to implement the system.

4. Design the modules:

• Next, you need to design the modules that will make up the system. This involves
defining the functions that each module will perform and the data that it will
manipulate.

5. Plan for scalability:

• As you design the system, you need to consider how it will scale. This involves
identifying potential bottlenecks and designing the system to handle increased
loads.

6. Consider security and privacy:

• Security and privacy should be a key consideration in system design. This involves
identifying potential security threats and designing the system to mitigate them.

7. Test and validate:

• Once the system design is complete, you need to test and validate it. This involves
creating test cases and scenarios that simulate real-world usage and verifying
that the system meets the requirements.

Overall, system design is a complex process that requires careful planning and attention to detail.
By following these steps, you can create a system design that meets the needs of your users and
your business.

Approaching a Design Problem

1. Breaking Down the Problem

When you are given a Design Problem start breaking it down into small components. These
components can be Services or Features which you need to implement in the System.

• Initially, a System given to be designed can have a large number of features and you are
not expected to design everything if it’s an Interview.
 • Ask the customers about the Features you are planning to put in your system. Is there
anything else you should be putting there? Any Feature? Any Service? … Ask!

2. Communicating your Ideas

Communicate well with customers:

• While designing the system keep him in the loop.

• Discuss your process out loud.

• Try to demonstrate your design clearly on the whiteboard with flowcharts and diagrams.

• Describe your ideas to your interviewer, how you have planned to tackle the problem of
scalability, how you will be designing your database, and many others.

3. Assumptions that make sense

Make some reasonable assumptions while you are designing the System.

Suppose you have to assume the number of requests the system will be processed per day, the
number of database calls made in a month, or the efficiency rate of your Caching System. These
are some of the numbers you need to assume while designing. Try to keep these numbers as
reasonable as possible. Back up your assumption with some solid facts and figures.

Important points to consider when designing a software system:

1. Scalability: The system should be designed to handle increased loads and be able to
scale horizontally or vertically as needed.

2. Performance: The system should be designed to perform efficiently and effectively, with
minimal latency and response time.

3. Reliability: The system should be reliable and available, with minimal downtime or
system failures.

4. Security: The system should be designed with security in mind, including measures to
prevent unauthorized access and protect sensitive data.

5. Maintainability: The system should be designed to be easy to maintain and update, with
clear documentation and well-organized code.

6. Interoperability: The system should be designed to work seamlessly with other systems
and components, with clear and well-defined interfaces.

7. Usability: The system should be designed to be user-friendly and intuitive, with a clear
and consistent user interface.

8. Cost-effectiveness: The system should be designed to be cost-effective, with a focus on

minimizing development and operational costs while still meeting the requirements.