Requirements

Architecture

==Conway's law== says structures of software systems are copies of the organization structures.

	Monolithic ==Service==	Micro Services
Productivity, when teams and codebases are small	✅ High	❌ Low
==Productivity, when teams and codebases are large==	❌ Low	✅ High (Conway's law)
==Requirements on Engineering Quality==	❌ High (under-qualified devs break down the system easily)	✅ Low (runtimes are segregated)
Dependency Bump	✅ Fast (centrally managed)	❌ Slow
Multi-tenancy support / Production-staging Segregation	✅ Easy	❌ Hard (each individual service has to either 1) build staging env connected to others in staging 2) Multi-tenancy support across the request contexts and data storage)
Debuggability, assuming same modules, metrics, logs	❌ Low	✅ High (w/ distributed tracing)
Latency	✅ Low (local)	❌ High (remote)
DevOps Costs	✅ Low (High on building tools)	❌ High (capacity planning is hard)

Combining monolithic ==codebase== and micro services can bring benefits from both sides.

consistent hashing sharded by geohash
data is transient, in memory, and thus there is no need to replicate. (CAP: AP over CP)
single-threaded or locked matching in a shard to prevent double dispatching

==The key is to have an async design==, because payment systems usually have a very long latency for ACID transactions across multiple systems.

low latency with caching
UserProfile Service has the challenge to serve users in increasing types (driver, rider, restaurant owner, eater, etc) and user schemas in different regions and countries.