🏗️System Design

System Design Overview

Updated 2026-04-20

2 min read

Introduction

System design is the process of defining the architecture, modules, interfaces, and data for a system to satisfy specified requirements. It is a critical skill for senior software engineers, as it focuses on building scalable, reliable, and maintainable systems.

Key Concepts in System Design

1. Scalability

Scalability is the capability of a system to handle a growing amount of work, or its potential to be enlarged to accommodate that growth.

Vertical Scaling (Scaling Up): Adding more power (CPU, RAM) to an existing machine.
Horizontal Scaling (Scaling Out): Adding more machines to your pool of resources. Horizontal scaling is generally preferred in modern architectures because it provides redundancy.

2. High Availability (HA)

High availability refers to systems that are durable and likely to operate continuously without failure for a long time. It is measured in "nines" (e.g., 99.999% uptime). HA is achieved by eliminating single points of failure using load balancers and redundant databases.

3. Caching

Caching involves storing copies of frequently accessed data in a temporary, fast-access location (like RAM using Redis or Memcached). This drastically reduces the load on primary databases and improves response times.

4. Load Balancing

A load balancer acts as a traffic cop, routing client requests across all servers capable of fulfilling those requests in a manner that maximizes speed and capacity utilization.

5. CAP Theorem

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

Consistency: Every read receives the most recent write or an error.
Availability: Every request receives a non-error response.
Partition Tolerance: The system continues to operate despite an arbitrary number of messages being dropped by the network.

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Key Concepts in System Design

1. Scalability

Scalability is the capability of a system to handle a growing amount of work, or its potential to be enlarged to accommodate that growth.

Vertical Scaling (Scaling Up): Adding more power (CPU, RAM) to an existing machine.

Horizontal Scaling (Scaling Out): Adding more machines to your pool of resources. Horizontal scaling is generally preferred in modern architectures because it provides redundancy.