LESSON 126 / 215·2 min readIntermediate

Shared MERN architecture

Must knowConcept lesson

01 Understand02 Recall 03 Prepare

Words made simple

A few useful meanings before you read the explanation.

AI: Software techniques for tasks such as recognizing patterns, understanding language or generating content.
API: A way for one piece of software to ask another for data or an action. A claims API might return the current status of a claim.
LLM: A model trained to work with language. It can write or summarize text, but its answer still needs checking against reliable information.

More words from this lesson

Vector: An ordered list of numbers. An embedding is a vector used to represent content for tasks such as similarity search.
Retrieval: Finding and fetching information that is useful for the current question.
Agent: An application that uses a model to choose its next action within defined limits. It can use tools and continue through several steps.
Durable: Able to retain progress and recover across interruptions. Durable workflows require appropriate storage and retry behavior.
Authorization: Checking what that identity is allowed to read or do. Being logged in does not grant access to every record.

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

Architecture at a glanceFollow the arrows to see how the parts connect.

Preparing the architecture diagram…

Read the full diagram flow

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.

PAUSE & RECALL