System design cheat sheet

It can be used for interviews or assessments.

1. Understand problem and scope:

• Recognize stakeholders and prioritize them. Create RACI matrix
• Understand business drivers of the project
• Recognize end-users of the project and understand how they will use that system
• Check functional requirements
• Define external dependencies
• Suggest additional features
• Remove items that interviewer considers out of scope

2. Think about constraints and non-functional requirements:

• (use PASS ME if you do not remember all of NFRs)
• Recognize number of users
• Estimate users growth rate (for the next year/next 5 years)
• Define average response time
• Understand database size (current / for the next year/ for the next 5 years)
• Understand storage size (current / for the next year/ for the next 5 years)
• Recognize security needs
• Define acceptable downtime of the system
• Recognize number of requests (per month/per second)
• Estimate reads vs. writes operations percentage
• Define time to market
• Check customer related nfr: legacy/proprietary soft, etc

3. Detect Architecture Significant Requirements

• Mix between FRs and NFRs to detect ASRs

4. Abstract design:

• Choose which architectural views to define based on the stakeholders matrix. Use common C4/4+1/etc otherwise
• Choose Architecture Style (Monolith, SOA - microservices, layered architecture, etc)
• Choose between cloud solution or on-premise servers
• Consider authentication/authorization and privacy
• Suggest security rules and protocols
• Define infrastructure: load balancing, messaging
• Make rough overview of any key algorithm that drives the service
• Consider bottlenecks and determine solutions
• Choose storage type (SQL or NoSQL)
• Understand what data should be cached and how to improve performance/security/availability with caching
• Choose monitoring system and logging. Analytics and automatically reboot system in case of exceptions
• Define separation between public and restricted areas