The following text is from "System Design Interview" by Alex Xu.
The following techniques can be applied to scale a system to support millions of users:
- Keep web tier stateless
- Build redundancy at every tier
- Cache data as much as you can
- Support multiple data centers
- Host static assets in CDN
- Scale your data tier by sharding
- Split tiers into individual services
- Favor asynchronous communication (e.g., message queues)
- Monitor your system and use automation tools
