Scalability

• It's the measure of a system's ability to handle a growing amount of work by adding resources to the system
• The resources need to be well managed in order to be used effectively and avoid overheads
• Solutions
• LB
• DB Sharding
• API gateway (organization scalability/flexibility - decouple the frontend from the internal structure)

Vertical Scalability (scale up)

• Add or upgrade existing resources on a single computer
• E.g., more memory, cpu
• Any application can benefit from it (node code changes required)

Horizontal Scalability (scale out)

• Add more resources in form of new instances/machines
• No limit on scalability
• The system should be designed to scale horizontally (sometimes not easily refactored, e.g., concurrency issues)
• Increased complexity, coordination overhead

Team/Org Scalability

• More engineers
• Better to have smaller groups of engineers each working on a module/service of the system