Shared MERN architecture

🔴 MUST KNOW · Your existing backend architecture stays useful; AI becomes a controlled dependency.

flowchart TD
  UI[Next.js / React] --> API[Node API: auth, validation, quotas]
  API --> AI[AI service: context, models, routing]
  AI --> L[Approved LLM adapter/gateway]
  AI --> G[Optional agent / LangGraph]
  G --> T[Authorized tools / optional MCP facade]
  AI --> R[Retrieval service / vector index]
  T --> DB[MongoDB or PostgreSQL business services]
  API --> Q[Queue / durable workflow]
  Q --> W[Node workers / optional Python FastAPI workers]
  W --> R
  API --> C[Redis: scoped caches and counters]

• Next.js renders the interface and safe streamed events.
• Node authenticates users and owns the application boundary.
• The AI service manages prompts, context, and models.
• Graphs are optional execution control.
• Tools enforce business operations.
• Retrieval provides evidence.
• Queues run long work.
• Python is introduced for document/model/numerical capabilities when it provides a practical benefit.
• Redis supports caches and rate limits, while the primary database retains durable records.