System Design - Approach

System design interview questions have become a standard part of software engineering interview process, especialy for senior level roles. Most candidates struggle with system design interview questions; either because they do not have the experience in designing large-scale systems, or because they have not prepared for the open-ended and unstructured nature of such questions.

There are many ways to prepare for and answer a system design interview question. Below is one way that uses a 7 step approach to solve system design interview questions.

Step 1 - Clarify Requirements and Determine Scope

• Who are users of the system?
• People?
• Systems?
• Processes?

• What features and functionality are in scope?

• What actions are performed on the system?
• Writes?
• Gets?
• Updates?
• Deletes?

• Does the system have a UI? Is UI design in scope for this interview?

Step 2 - Estimate for Scale (Back of the Envelope Estimations)

Ask questions to interviewer to understand the requirements and scope for the interview. Below are some of the questions for most systems.

• Estimate scale
• Number of requests per second
• Number of Read vs Write requests.
• Estimate storage
• Estimate size of write request
• Estimated storage requirement per year
• Estimate bandwidth
• Payload size of read and write requests
• Bandwidth requirement per second

Step 3 - High Level Design

Include following components if applicable

• Client
• DNS Server
• DNS Server
• UI/Web layer (react.js, angular.js, backbone.js, etc.)
• Service/API Layer (app servers, micro services, etc.)
• Data layer (database, image storage, file server, etc.)
• Async/off-line processing (messaging queue, kafka, .etc)

Step 4 - High Level Design for Scale

Sketch High Level Design For Scale
Include following components if applicable

• Load-balancers
• Caching
• Data partitioning
• Data replication

Step 5 - Data Model (Optional)

• Define entities
• Define interaction between entities
• SQl, NoSQL or Both?

Step 6 - Define the System Interface Definition (optional)

• Services
• API Endpoints for each service

Step 7 - Deep Dive (optional)

Deep dive into one or more of key components

• Any specific algoriths to use
• Address any bottlenecks