Scaling for Millions of Users

Scenario : A system that caters large number of users with a web front-end and a mobile app.

Things to consider

• Choice of Database

  • For most cases relational database like MySQL would work
  • Things to consider when going for NoSQL
    • Application requires super law latency
    • Unstructured data or data has no relations
    • Need to store a massive amount of data

• Scale the application tier

  • Decide whether horizontal or vertical scaling
  • Vertical scaling is limited by CPU, Memory, Space and cost
  • Horizontal scaling require adding new components like load balancers and changing the application to be able to share load

• Scale the database (database-scaling )

  • Database Replication
  • Database Sharding

• Use Caching and CDN for static assets

  • Avoid frequent calls to database
  • Improve performance

• Make the application/web tier stateless

  • Mitigates issue with stateless web tier/sticky sessions
  • Easier horizontal scaling

• Support multiple data centers

  • Geo Routing
  • Geo DNS
  • Disaster Recovery
  • Availability

• Decouple the components and make processes async, Introduce message queues

  • RabbitMQ
  • Kafka

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References:

• System Design Interview – An insider’s guide, Second Edition - Alex Xu