What are the 3 phases of system design?

System design can be broken down into three main phases: Conceptual Design, Logical Design, and Physical Design. Each phase serves a distinct purpose in the process of creating a scalable, efficient, and reliable system.

1. Conceptual Design

This phase is all about understanding the requirements and high-level architecture of the system. It’s the starting point where you focus on what the system needs to do and define the broad components that will be involved.

Key Tasks:

• Clarify Requirements: Determine both functional requirements (what the system does) and non-functional requirements (performance, scalability, reliability, etc.).
• Identify High-Level Components: Break the system into major components like databases, APIs, caching layers, and services.
• Focus on High-Level Goals: During conceptual design, the focus is on understanding how to meet the system's key goals (e.g., scalability, fault tolerance).

Example:

For a video streaming service, the conceptual design would outline components like:

• A content delivery network (CDN) for delivering videos.
• Databases to store video metadata and user information.
• API gateways for handling user requests.

2. Logical Design

In the logical design phase, you define the detailed structure of the system, focusing on how components interact and how data flows through the system. This is where you refine the initial conceptual ideas and make design choices to ensure the system works efficiently.

Key Tasks:

• Define Data Flow: Specify how data will move between components (e.g., from the user’s request to the database and back).
• Determine Communication: Design how different components (e.g., microservices) communicate via APIs, message queues, or databases.
• Architect Decisions: Make decisions about system architecture, such as whether to use microservices or a monolithic architecture.
• Choose Databases and Technologies: Decide on the type of database (SQL vs. NoSQL), caching strategies (Redis, Memcached), and other technologies.

Example:

For a social media platform, the logical design would focus on:

• How the feed service pulls data from a database to create a user’s timeline.
• How the cache stores frequently accessed posts.
• How APIs allow the frontend to interact with the backend.

3. Physical Design

The physical design phase focuses on the implementation details and the actual infrastructure that will be used to build the system. Here, you map the logical design onto physical servers, databases, and networks.

Key Tasks:

• Choose Infrastructure: Decide whether to use cloud services (e.g., AWS, Google Cloud) or on-premise hardware.
• Optimize for Performance: Determine how to optimize the system with load balancers, horizontal scaling, replication, and database sharding.
• Deployment Strategy: Plan how to deploy and maintain the system, including CI/CD pipelines, monitoring, and logging.
• Handle Failures and Redundancy: Implement strategies for fault tolerance, backups, and failover to ensure the system is resilient to failures.

Example:

For an e-commerce platform, the physical design would define:

• Which databases (e.g., MySQL, DynamoDB) will be used for product storage.
• How load balancers will distribute traffic across servers.
• How the system will handle server outages and ensure high availability.

Conclusion

The three phases of system design—Conceptual Design, Logical Design, and Physical Design—work together to create a comprehensive system. Each phase progressively adds more detail, starting with high-level requirements and ending with the specific infrastructure and technologies needed to implement the system. This structured approach helps ensure that the final system is scalable, reliable, and able to meet the defined requirements.