FastAPI Microservices Setup

 Below is a real-world FastAPI microservices setup, explained step by step, and mapped to how companies actually do it in production. I’ll also relate it to Spring Boot microservices, so it’s easy to grasp.

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FastAPI Microservices Setup (Production-Ready Guide)

1️⃣ What Is a FastAPI Microservices Architecture?

Instead of one large backend, you create multiple small FastAPI services, each responsible for one business capability.

Example services:

• Auth Service

• User Service

• Notification Service

• Event / Integration Service

• Reporting Service

Each service:

• Has its own codebase

• Has its own database (recommended)

• Can be deployed and scaled independently

---

2️⃣ High-Level Architecture

Frontend (Angular / React / Mobile)
          ↓
      API Gateway
          ↓
 ┌────────┬─────────┬──────────┐
 | Auth   | Users   | Events   |  FastAPI services
 |Service | Service | Service  |
 └────────┴─────────┴──────────┘
          ↓
 Databases / Queues / Caches

---

3️⃣ Example Microservices Folder Structure

microservices/
│
├── api-gateway/
│   └── app/
│       └── main.py
│
├── auth-service/
│   └── app/
│       ├── main.py
│       └── api/
│
├── user-service/
│   └── app/
│       ├── main.py
│       └── api/
│
├── event-service/
│   └── app/
│       ├── main.py
│       └── api/
│
├── docker-compose.yml
└── README.md

👉 Each service is a separate FastAPI app.

---

4️⃣ Service-to-Service Communication

Option 1: REST (Most Common)

• HTTP calls between services

• Use async HTTP clients (httpx)

User Service → Auth Service

Option 2: Message Queue (Recommended for scale)

• Kafka / RabbitMQ / AWS SQS

• Event-driven communication

Event Service → Queue → Notification Service

---

5️⃣ API Gateway (Very Important)

Companies use:

• Nginx

• Kong

• FastAPI Gateway

Responsibilities:

• Routing

• Authentication

• Rate limiting

• Logging

Simple FastAPI Gateway Example

@app.api_route("/{path:path}", methods=["GET", "POST"])
async def proxy(path: str, request: Request):
    async with httpx.AsyncClient() as client:
        response = await client.request(
            request.method,
            f"http://user-service/{path}",
            headers=request.headers.raw,
            content=await request.body()
        )
    return Response(response.content)

---

6️⃣ Authentication Strategy

Central Auth Service (Recommended)

Flow:

1. User logs in → Auth Service

2. JWT token issued

3. Other services validate JWT

Each service:

• Validates token

• Does not store auth logic

📌 Same idea as Spring Security + JWT.

---

7️⃣ Database Strategy

Best practice:

• One database per service

Examples:

• Auth Service → PostgreSQL

• User Service → MongoDB

• Event Service → NoSQL / Kafka

❌ Avoid shared databases between services.

---

8️⃣ Async & Performance Setup

Run services using:

Gunicorn + Uvicorn workers

Example:

gunicorn app.main:app -k uvicorn.workers.UvicornWorker -w 4

---

9️⃣ Docker Setup (Per Service)

Dockerfile (Common for all services)

FROM python:3.11-slim

WORKDIR /app
COPY requirements.txt .
RUN pip install -r requirements.txt

COPY app app
CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]

---

🔟 docker-compose (Local Development)

version: "3.8"
services:
  auth-service:
    build: ./auth-service
    ports:
      - "8001:8000"

  user-service:
    build: ./user-service
    ports:
      - "8002:8000"

  event-service:
    build: ./event-service
    ports:
      - "8003:8000"

---

1️⃣1️⃣ Configuration Management

Use:

• .env files

• Environment variables

• Secrets manager (in prod)

Example:

AUTH_SERVICE_URL=http://auth-service:8000

---

1️⃣2️⃣ Logging & Monitoring

Production services include:

• Structured logging

• Request tracing (request ID)

• Metrics (Prometheus)

• Central log aggregation

---

1️⃣3️⃣ Scaling Strategy

• Stateless services

• Horizontal scaling

• Kubernetes HPA

• Load balancing via ingress

---

1️⃣4️⃣ FastAPI vs Spring Boot Microservices

Aspect	FastAPI	Spring Boot
Startup time	Very fast	Slower
Resource usage	Low	Higher
Async	Simple	Complex
Enterprise tooling	Moderate	Excellent

Many companies use:

Spring Boot → Core services
FastAPI     → Integration & API services

---

1️⃣5️⃣ Common Mistakes to Avoid

❌ Sharing databases
❌ Tight coupling between services
❌ Missing API gateway
❌ Blocking calls in async routes
❌ No centralized auth

---

Final Thoughts

FastAPI microservices are:

• Lightweight

• Fast

• Easy to scale

• Perfect for integration-heavy systems

For someone with your background:

• Spring Boot → Core business logic

• FastAPI → Microservices, integrations, ML APIs

This combo is very powerful in modern architectures.

FastAPI Project Structure

 

Production Best Practices

1️⃣ Recommended Folder Structure

fastapi-app/
│
├── app/
│   ├── main.py              # Entry point (like SpringBootApplication)
│   │
│   ├── core/                # Core configs (security, settings)
│   │   ├── config.py        # App settings (env based)
│   │   ├── security.py      # Auth, JWT, OAuth2
│   │   └── logging.py
│   │
│   ├── api/                 # API layer (Controllers)
│   │   ├── v1/
│   │   │   ├── router.py    # API router aggregation
│   │   │   └── endpoints/
│   │   │       ├── users.py
│   │   │       ├── auth.py
│   │   │       └── health.py
│   │
│   ├── models/              # DB models (Entities)
│   │   ├── user.py
│   │   └── base.py
│   │
│   ├── schemas/             # Pydantic schemas (DTOs)
│   │   ├── user.py
│   │   └── auth.py
│   │
│   ├── services/            # Business logic (Service layer)
│   │   ├── user_service.py
│   │   └── auth_service.py
│   │
│   ├── repositories/        # DB access layer
│   │   └── user_repo.py
│   │
│   ├── db/                  # Database setup
│   │   ├── session.py
│   │   └── init_db.py
│   │
│   ├── middlewares/         # Custom middleware
│   │   └── request_log.py
│   │
│   ├── utils/               # Utilities/helpers
│   │   └── date_utils.py
│   │
│   └── tests/               # Unit & integration tests
│       └── test_users.py
│
├── requirements.txt
├── Dockerfile
├── docker-compose.yml
├── .env
└── README.md

---

2️⃣ Mapping to Spring Boot (So It Feels Familiar)

Spring Boot	FastAPI
@SpringBootApplication	main.py
Controller	api/endpoints
Service	services
Repository	repositories
Entity	models
DTO	schemas
application.yml	config.py / .env
Filters	middlewares

---

3️⃣ main.py – Application Entry Point

from fastapi import FastAPI
from app.api.v1.router import api_router

app = FastAPI(title="FastAPI App")

app.include_router(api_router, prefix="/api/v1")

➡ Similar to:

@SpringBootApplication
public class App { }

---

4️⃣ Router Aggregation (Like Controller Scanning)

api/v1/router.py

from fastapi import APIRouter
from app.api.v1.endpoints import users, auth, health

api_router = APIRouter()
api_router.include_router(users.router, prefix="/users", tags=["Users"])
api_router.include_router(auth.router, prefix="/auth", tags=["Auth"])
api_router.include_router(health.router, prefix="/health", tags=["Health"])

---

5️⃣ Controller Layer (Endpoints)

api/v1/endpoints/users.py

from fastapi import APIRouter
from app.schemas.user import UserCreate

router = APIRouter()

@router.post("/")
def create_user(user: UserCreate):
    return {"message": "User created"}

---

6️⃣ Schema (DTO)

schemas/user.py

from pydantic import BaseModel

class UserCreate(BaseModel):
    name: str
    email: str

---

7️⃣ Service Layer (Business Logic)

services/user_service.py

def create_user(user):
    # business rules here
    return user

---

8️⃣ Repository Layer (DB Access)

repositories/user_repo.py

def save(user):
    pass

---

9️⃣ Dependency Injection (FastAPI Style)

from fastapi import Depends

def get_user_service():
    return UserService()

@router.get("/{id}")
def get_user(id: int, service=Depends(get_user_service)):
    return service.find(id)

➡ Similar concept to @Autowired.

---

🔟 Environment Configuration

.env

DB_URL=mongodb://localhost:27017/app
JWT_SECRET=secret

config.py

from pydantic import BaseSettings

class Settings(BaseSettings):
    DB_URL: str
    JWT_SECRET: str

settings = Settings()

---

1️⃣1️⃣ Testing Structure

tests/
 ├── test_users.py
 └── conftest.py

Uses:

• pytest

• TestClient

---

1️⃣2️⃣ Production-Grade Tips

✅ Keep business logic out of controllers
✅ Use async DB drivers
✅ Version your APIs (/v1)
✅ Use dependency injection properly
✅ Add middleware for logging
✅ Use Docker for consistency

---

1️⃣3️⃣ Minimal Structure (For Small Services)

app/
 ├── main.py
 ├── routes.py
 ├── schemas.py
 └── services.py

Use this only for small microservices.

---

Final Thoughts

FastAPI doesn’t force structure like Spring Boot, but teams must enforce discipline.

If you follow the above structure:

• Code stays clean

• Team collaboration improves

• Scaling becomes easy

FastAPI Interview Questions and Answers (Beginner to Advanced)

FastAPI has quickly become one of the most popular Python frameworks for building high-performance APIs. As a result, FastAPI interview questions are now common in backend, microservices, and AI/ML roles.

This post covers commonly asked FastAPI interview questions with simple and clear answers, from basic concepts to advanced topics.

---

1️⃣ What is FastAPI?

FastAPI is a modern, high-performance Python web framework used to build REST APIs quickly.
It is built on Starlette for web handling and Pydantic for data validation.

Key features:

• Fast performance

• Automatic API documentation

• Built-in request validation

• Async support

---

2️⃣ Why is FastAPI faster than Flask or Django?

FastAPI is faster because:

• It uses ASGI instead of WSGI

• Supports async/await

• Uses Uvicorn (high-performance server)

• Minimizes blocking IO

This makes FastAPI ideal for high-concurrency APIs.

---

3️⃣ What is ASGI and how is it different from WSGI?

WSGI	ASGI
Synchronous	Asynchronous
One request per thread	Event-loop based
Used by Flask, Django	Used by FastAPI

FastAPI uses ASGI, enabling better scalability.

---

4️⃣ What are Pydantic models?

Pydantic models are used for:

• Request body validation

• Response validation

• Type enforcement

Example:

class User(BaseModel):
    name: str
    age: int

FastAPI automatically validates incoming JSON against this model.

---

5️⃣ How does FastAPI generate Swagger documentation?

FastAPI automatically generates OpenAPI (Swagger) documentation using:

• Python type hints

• Route definitions

• Pydantic models

Available at:

• /docs (Swagger UI)

• /redoc (ReDoc)

---

6️⃣ What is dependency injection in FastAPI?

Dependency Injection (DI) allows reusable components like:

• Database sessions

• Authentication logic

• Common validations

Example:

Depends(get_db)

It improves code reusability and testability.

---

7️⃣ How do you handle authentication in FastAPI?

FastAPI supports:

• OAuth2

• JWT

• API Keys

• Basic Auth

It provides built-in security utilities like:

OAuth2PasswordBearer

---

8️⃣ What is the difference between def and async def in FastAPI?

def	async def
Blocking	Non-blocking
CPU-bound tasks	IO-bound tasks
Simpler	High concurrency

Use async def when calling:

• Databases

• External APIs

• Message queues

---

9️⃣ How does FastAPI handle request validation errors?

FastAPI:

• Automatically validates requests

• Returns HTTP 422 (Unprocessable Entity)

• Provides clear error messages

No manual validation code is required.

---

🔟 How do you connect FastAPI to a database?

FastAPI supports:

• SQLAlchemy (SQL)

• Motor (MongoDB)

• Async ORMs

Typically:

• Create a DB session dependency

• Inject it using Depends()

---

1️⃣1️⃣ How do you write unit tests in FastAPI?

FastAPI uses:

• pytest

• TestClient

Example:

def test_health():
    response = client.get("/health")
    assert response.status_code == 200

---

1️⃣2️⃣ How is FastAPI deployed in production?

Typical production setup:

Nginx
 ↓
Gunicorn + Uvicorn workers
 ↓
FastAPI app

Often containerized using Docker and orchestrated with Kubernetes.

---

1️⃣3️⃣ How does FastAPI compare to Spring Boot?

FastAPI	Spring Boot
Python	Java
Async-first	Thread-based
Minimal config	Heavy config
Fast development	Enterprise stability

Many companies use both together.

---

1️⃣4️⃣ What are background tasks in FastAPI?

Background tasks allow execution after response is sent.

Used for:

• Sending emails

• Logging

• Notifications

Example:

BackgroundTasks

---

1️⃣5️⃣ What are common FastAPI interview mistakes?

❌ Using def instead of async def
❌ Blocking calls inside async routes
❌ Ignoring dependency injection
❌ Not handling exceptions properly
❌ Poor project structure

---

Advanced FastAPI Interview Questions (For Experienced Devs)

• How does FastAPI handle concurrency internally?

• How do you implement rate limiting?

• How do you use middleware in FastAPI?

• How do you secure APIs using OAuth2 + JWT?

• How do you scale FastAPI horizontally?

• How do you integrate FastAPI with Kafka / RabbitMQ?

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Final Thoughts

FastAPI is not just a framework, it’s a modern API philosophy:

• Clean code

• High performance

• Strong typing

• Developer-friendly

FastAPI vs Spring Boot

 

FastAPI vs Spring Boot: Which One Should You Choose?

In the world of backend development, Spring Boot has been the gold standard for years—especially in enterprise Java applications.
But recently, FastAPI has gained massive popularity in the Python ecosystem for building modern APIs.

So the big question is:

👉 FastAPI vs Spring Boot — which one is better?
👉 Should Java developers care about FastAPI?

Let’s compare them from a real-world, production perspective.

---

What is Spring Boot?

Spring Boot is a Java-based framework that simplifies building enterprise-grade applications.

It provides:

• Dependency Injection

• Security

• Transaction management

• Database integration

• Production-ready tooling

Spring Boot is widely used in:

• Banking

• Insurance

• Government systems

• Large enterprises

---

What is FastAPI?

FastAPI is a modern Python framework designed specifically for building high-performance APIs.

It focuses on:

• Speed

• Simplicity

• Automatic validation

• Automatic documentation

FastAPI is widely used in:

• Microservices

• Startups

• AI / ML platforms

• Integration-heavy systems

---

Core Comparison: FastAPI vs Spring Boot

1️⃣ Language & Ecosystem

Aspect	FastAPI	Spring Boot
Language	Python	Java
Ecosystem	Lightweight, fast	Enterprise-grade
Verbosity	Very low	High

Verdict:
Spring Boot is structured and strict. FastAPI is flexible and fast to develop.

---

2️⃣ Development Speed

	FastAPI	Spring Boot
Boilerplate	Minimal	Heavy
API setup time	Minutes	30–60 minutes
Configuration	Very less	Extensive

FastAPI allows teams to ship APIs much faster.

---

3️⃣ Performance & Concurrency

	FastAPI	Spring Boot
Concurrency model	Async (event loop)	Thread-based
Best for	IO-heavy APIs	CPU-heavy logic
Latency	Lower	Slightly higher

FastAPI shines in:

• Webhooks

• Event ingestion

• High-concurrency APIs

---

4️⃣ Validation & API Contracts

	FastAPI	Spring Boot
Request validation	Automatic	Annotations
OpenAPI spec	Auto-generated	Manual setup
Error messages	Clear	Verbose

FastAPI’s validation feels like:

DTO + Validation + Swagger — without extra configuration

---

5️⃣ API Documentation (Major Difference)

FastAPI provides:

• Swagger UI at /docs

• ReDoc at /redoc

No extra setup needed.

In Spring Boot:

• Swagger/OpenAPI requires manual configuration

• Docs often go out of sync

📌 Frontend teams love FastAPI for this reason alone.

---

6️⃣ Async Support

	FastAPI	Spring Boot
Async support	Native	WebFlux
Complexity	Simple	High
Learning curve	Easy	Steep

Many Java teams avoid WebFlux due to complexity, while FastAPI makes async natural.

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7️⃣ Enterprise Features

Feature	FastAPI	Spring Boot
Security	Good	Excellent
Transactions	Manual	Strong
AOP	❌	✅
Dependency Injection	Basic	Advanced

Spring Boot clearly wins in enterprise governance and safety.

---

8️⃣ Database & ORM Support

	FastAPI	Spring Boot
ORM	SQLAlchemy	Hibernate
MongoDB	Motor	Spring Data Mongo
Maturity	Medium	Very High

Spring Data is more mature for large teams and long-term projects.

---

When to Use FastAPI?

Choose FastAPI if you are building:

• Microservices

• API gateways

• Integration platforms

• Event-driven systems

• AI / ML APIs

• Backend for React / Angular apps

---

When to Use Spring Boot?

Choose Spring Boot if you are building:

• Enterprise systems

• Banking or finance apps

• Complex transactional workflows

• Long-term systems (10–15 years lifespan)

• Large, regulated platforms

---

Real-World Architecture (Very Common)

Many companies use both together:

Spring Boot → Core business logic
FastAPI     → API layer, integrations, ML services

This hybrid approach offers stability + speed.

---

Final Verdict

FastAPI is not a replacement for Spring Boot.
It is a complement.

• Spring Boot = Enterprise backbone

• FastAPI = Fast, modern API layer

For experienced Java developers, learning FastAPI adds a powerful new skill and opens doors to modern architectures and AI-driven systems.

---

Conclusion

If you want:

• Faster development

• Cleaner APIs

• Better API documentation

• Modern async architecture

👉 FastAPI is worth learning.

If you want:

• Enterprise reliability

• Strong governance

• Long-term maintainability

👉 Spring Boot remains unbeatable.

What is FastAPI

 

What is FastAPI? A Beginner-Friendly Guide

In today’s world of web and mobile applications, APIs are the backbone of modern software. If you’re a Python developer—or planning to become one—you’ve probably heard about FastAPI.

But what exactly is FastAPI, and why are companies adopting it so fast?
Let’s break it down in simple terms.

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What is FastAPI?

FastAPI is a modern Python web framework used to build REST APIs quickly and efficiently.

It is:

• 🚀 Fast (high performance)

• 🧠 Smart (automatic validation & documentation)

• ✨ Easy to use (less boilerplate code)

FastAPI was created to solve common problems developers face with older frameworks like Flask and Django when building APIs at scale.

---

Why is it called FastAPI?

FastAPI is fast because it is built on top of:

• Starlette → for web handling

• Pydantic → for data validation

This combination makes FastAPI one of the fastest Python frameworks, with performance comparable to Node.js and Go for API workloads.

---

A Simple FastAPI Example

Here’s how easy it is to create an API:

from fastapi import FastAPI

app = FastAPI()

@app.get("/hello")
def hello():
    return {"message": "Hello World"}

Run it, and your API is live!

---

Automatic API Documentation (Big Advantage)

One of FastAPI’s biggest strengths is automatic documentation.

Without writing any extra code, you get:

• Swagger UI → /docs

• ReDoc UI → /redoc

This is extremely useful for:

• Frontend developers

• QA teams

• API consumers

Your API docs are always up-to-date.

---

Built-in Data Validation

FastAPI automatically validates incoming requests using Python type hints.

Example:

from pydantic import BaseModel

class User(BaseModel):
    name: str
    age: int

If incorrect data is sent, FastAPI returns a clear error message—no manual checks needed.

---

Async Support (High Concurrency)

FastAPI supports async / await natively.

This makes it ideal for:

• Webhooks

• Event ingestion

• API integrations

• High traffic systems

Example:

@app.get("/items")
async def get_items():
    return ["item1", "item2"]

---

Where is FastAPI Used in Real Life?

Companies use FastAPI in production for:

• 🔹 Microservices

• 🔹 Backend for React / Angular apps

• 🔹 CRM integrations (Salesforce, Marketo, etc.)

• 🔹 Event processing systems

• 🔹 AI / ML model serving

• 🔹 API gateways

Many startups and even large companies use FastAPI alongside Java Spring Boot systems.

---

FastAPI vs Flask vs Django

Feature	FastAPI	Flask	Django
Performance	⭐⭐⭐⭐⭐	⭐⭐⭐	⭐⭐
Auto Docs	✅	❌	❌
Validation	✅	❌	⚠️
Async	✅	❌	⚠️
Best for	APIs	Small apps	Full web apps

---

When Should You Use FastAPI?

Use FastAPI if you:

• Need to build APIs quickly

• Want high performance

• Work on microservices

• Are building AI/ML APIs

• Want clean and maintainable code

---

When Not to Use FastAPI?

Avoid FastAPI if:

• You need a full server-side HTML framework

• You want heavy built-in admin panels (Django is better here)

---

Final Thoughts

FastAPI has become a game-changer in the Python ecosystem.

It combines:

• ⚡ Speed

• 🧩 Simplicity

• 📄 Excellent documentation

• 🛡️ Strong validation

If you are a backend developer or want to build scalable APIs in Python, FastAPI is absolutely worth learning.