Dongfeng Gu

How to answer system design question?

Sunday. May 03, 2020 - 1 min

system design interview

Steps to solve system design interview questions

Step 1: Clarify the function requirements
- Functional requirement, What specific features are we going to build?
- Non-Functional requirement,
  - How many users does the product have?
  - What are performance requirement for the system? Ex, Latency requirement, robustness, scalability, resilience, extendability
- What is the company’s technology stack? What dependencies we could use?
Step 2: Ask about the capacity estimation and constraints
- Make assumptions. (MAU, DAU, usage rate)
- Estimate traffic volume (Read and Write TPS)
- Estimate data size
- Estimate bandwidth
Step 3: Design System APIs.
- What are the Parameters for the APIs
- What are the APIs we want to support (CURD)
Step 4: Database Design
- Database schema
- Size of a single record
- What is the primary key, what are the attributes?
- DataType of each attributes
- What are the indexes?
- SQL or non-SQL
Step 5: Basic System Design and Algorithm
- List out the pros and cons for different design options
- Draw Component diagram.
Step 6: Data Partitioning and Replication
- How can we partition the database if we have a large amount of data?
  - Hash-Based partitioning
Step 7: Cache
- Which cache eviction policy should we use? Least Recently Used (LRU)
- How much memory will we use?
- How to update the replica of cache?
Step 8: Load Balancer
- Most simple version is the round robin approach.
- But we can also route traffic according to the avg latency for a single host. Less latency host can get more traffic.
Step 9: Purging or cleanup unused data.
- Clean data on the fly as part of a request
- Schedule service to clean up data once in a while
Step 10: Security and permissions request
- Who can have permission to access certain resources.
Step 11: Monitoring, alarms, metrics, dashboards, and operations