5. Building Block View

5.1 Level 1 — Containers

Container	Technology	Responsibility
React SPA	React / TypeScript	Renders UI, routes user actions to the appropriate service
Users Service	Python 3.12 / FastAPI	Authentication (JWT), user profiles, follow graph
Posts Service	Python 3.12 / FastAPI	Create/read posts, likes, aggregated timeline feed
Messaging Service	Python 3.12 / FastAPI	Direct messages, mentions
Users DB	PostgreSQL (users schema)	Persistent store for Users Service
Posts DB	PostgreSQL (posts schema)	Persistent store for Posts Service
Messaging DB	PostgreSQL (messaging schema)	Persistent store for Messaging Service

5.2 Level 2 — Internal Structure per Service

Users Service

Module	Responsibility
auth	JWT issuance (RS256), login, registration, email verification
profiles	CRUD for user profiles, avatar handling
follows	Follow / unfollow, follower/followee lists

Posts Service

Module	Responsibility
posts	Create, edit, delete posts
feed	Aggregate timeline from followed users; fan-out on read
likes	Like / unlike a post

Messaging Service

Module	Responsibility
conversations	Create and list direct-message conversations
messages	Send and retrieve messages within a conversation
mentions	Detect and store @mentions; notify Users Service

5.3 Cross-Context Interfaces

Caller	Callee	Endpoint	Purpose
Posts Service	Users Service	GET /users/{id}	Enrich post with author profile
Messaging Service	Users Service	GET /users/{id}	Enrich message with sender/recipient profile