# FastAPI-Lambda
**Drop-in replacement for FastAPI** - Optimized for AWS Lambda with minimal cold start overhead and package size.
[](https://pypi.org/project/fastapi-lambda/)
[](https://www.python.org/downloads/)
[](https://opensource.org/licenses/MIT)
[](https://pepy.tech/project/fastapi-lambda)
[](https://github.com/tsilicani/fastapi-lambda)
[](https://github.com/tsilicani/fastapi-lambda)
[](https://github.com/tsilicani/fastapi-lambda/actions/workflows/ci.yml)
---
## ⚠️ **EARLY DEVELOPMENT - NOT PRODUCTION READY**
> **WARNING:** This project is in **early alpha stage** and highly unstable.
>
> - 🚧 **Breaking changes** may occur without notice
> - 🐛 **Bugs and incomplete features** are expected
> - ❌ **NOT recommended for production use**
> - 📝 **API may change significantly** between versions
>
> Use at your own risk! For production workloads, consider:
> - [FastAPI](https://github.com/fastapi/fastapi) (original) with [Mangum](https://github.com/jordaneremieff/mangum)
> - Wait for a stable 1.0.0 release of this project
---
## 🚀 Why FastAPI-Lambda?
FastAPI-Lambda is a lightweight, Lambda-optimized framework that maintains FastAPI's intuitive API while removing unnecessary dependencies and features incompatible with serverless environments.
**Key Benefits:**
- ⚡ **<500ms cold starts** - No ASGI layer overhead
- 🔄 **Same FastAPI interfaces** - Minimal code changes required
- 📦 **Lightweight** - Pydantic v2.7+ only (single dependency)
- 🎯 **Lambda-native** - Direct API Gateway event handling
- ✅ **Sync & Async** - Supports both `def` and `async def` endpoints
## 📊 Performance Comparison
| Metric | Standard FastAPI | FastAPI-Lambda |
|--------|-----------------|----------------|
| Cold Start | 1-2s (with ASGI) | <500ms (direct) |
| Package Size | ~5.8MB | ~3MB (48% reduction) |
| Dependencies | Starlette + extras | Pydantic only |
| Memory Overhead | ASGI + middleware | Minimal |
## 📥 Installation
```bash
pip install fastapi-lambda
```
## 🎯 Quick Start
```python
from fastapi_lambda import FastAPI
app = FastAPI()
# Both sync and async endpoints work!
@app.get("/")
def root():
return {"message": "Hello from Lambda"}
@app.get("/async")
async def async_endpoint():
return {"message": "Async works too!"}
# Lambda handler
from fastapi_lambda import create_lambda_handler
lambda_handler = create_lambda_handler(app)
```
## 🔌 Deployment
### Lambda Function URL
```yaml
# serverless.yml
functions:
api:
handler: handler.lambda_handler
url:
cors: true
```
### API Gateway v1 (REST)
```yaml
functions:
api:
handler: handler.lambda_handler
events:
- http:
path: "/"
method: ANY
- http:
path: "{proxy+}"
method: ANY
```
### API Gateway v2 (HTTP)
```yaml
functions:
api:
handler: handler.lambda_handler
events:
- httpApi:
path: "/{proxy+}"
method: "*"
```
## ✅ Supported Features
### HTTP REST API
- ✅ All methods: GET, POST, PUT, DELETE, PATCH, OPTIONS, HEAD
- ✅ Path/Query/Header parameters
- ✅ Request body validation
- ✅ Response models
- ✅ **Sync and async endpoints**
### Validation & Serialization
- ✅ **Pydantic v2 only** (Rust-powered performance)
- ✅ Type-based validation
- ✅ JSON encoding/decoding
### Dependency Injection
- ✅ `Depends()` with sync/async functions
- ✅ Generator-based cleanup (`yield`)
- ✅ Dependency caching
- ✅ Request/Response injection
### OpenAPI Schema
- ✅ Automatic OpenAPI 3.1.0 schema generation
- ✅ JSON endpoint at `/openapi.json`
- ✅ Complete request/response documentation
- 📝 Use external tools: Swagger Editor, Postman, Insomnia
### Security
- ✅ HTTP Bearer (JWT tokens)
- ✅ Custom security schemes
## ❌ Removed Features (Lambda Incompatible)
| Feature | Why Removed | Alternative |
|---------|-------------|-------------|
| WebSockets | Lambda doesn't support persistent connections | Use AWS API Gateway WebSocket API separately |
| Background Tasks | Lambda stops after response | Use SQS/EventBridge |
| File Uploads | Payload size limits | Use S3 pre-signed URLs |
| Streaming Responses | 6MB Lambda limit | Return URLs to S3 |
| Swagger UI/ReDoc | Reduce package size | Use external tools with `/openapi.json` |
## 🧪 Testing
### Unit Tests
```bash
# Run all tests
npm run test
# With coverage
npm run test:cov
# Watch mode
npm run test:watch
```
### E2E Tests
```bash
# Setup (deploy to AWS)
npm run test:e2e:setup
# Run E2E tests
npm run test:e2e
```
E2E tests automatically run against **all 3 deployment types**:
- Lambda Function URL
- API Gateway v1 (REST)
- API Gateway v2 (HTTP)
See [tests/e2e/README.md](tests/e2e/README.md) for details.
## 📖 Documentation
- [E2E Testing Guide](tests/e2e/README.md)
- [Architecture & Design](.claude/CLAUDE.md)
## 🤝 Contributing
Contributions are welcome! Please ensure:
- ✅ Tests pass (`npm run test`)
- ✅ Coverage >80% (`npm run test:cov`)
- ✅ No linting errors (`npm run lint`)
- ✅ Type checking passes (`npm run typecheck`)
## 📜 License
This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details.
## 🙏 Credits
This project is inspired by and derived from [FastAPI](https://github.com/fastapi/fastapi) by Sebastián Ramírez, licensed under the MIT License.
**FastAPI-Lambda** is an independent fork optimized specifically for AWS Lambda environments. It maintains API compatibility with FastAPI while removing ASGI dependencies and features incompatible with serverless execution.
### Key Differences from FastAPI
- **No ASGI layer** - Direct Lambda event handling
- **Minimal dependencies** - Pydantic v2.7+ only
- **Lambda-optimized** - <500ms cold starts
- **Smaller package** - ~48% size reduction
For traditional web applications or features like WebSockets, use the original [FastAPI](https://github.com/fastapi/fastapi).
## 🔗 Related Projects
- [FastAPI](https://github.com/fastapi/fastapi) - Original FastAPI framework
- [Starlette](https://github.com/encode/starlette) - ASGI framework (removed in this fork)
- [Pydantic](https://github.com/pydantic/pydantic) - Data validation
- [Mangum](https://github.com/jordaneremieff/mangum) - ASGI adapter for AWS Lambda (alternative approach)
## 📧 Support
- **Issues**: [GitHub Issues](https://github.com/tsilicani/fastapi-lambda/issues)
- **Discussions**: [GitHub Discussions](https://github.com/tsilicani/fastapi-lambda/discussions)
---
Made with ❤️ for the serverless community
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"description": "# FastAPI-Lambda\n\n**Drop-in replacement for FastAPI** - Optimized for AWS Lambda with minimal cold start overhead and package size.\n\n[](https://pypi.org/project/fastapi-lambda/)\n[](https://www.python.org/downloads/)\n[](https://opensource.org/licenses/MIT)\n[](https://pepy.tech/project/fastapi-lambda)\n[](https://github.com/tsilicani/fastapi-lambda)\n[](https://github.com/tsilicani/fastapi-lambda)\n[](https://github.com/tsilicani/fastapi-lambda/actions/workflows/ci.yml)\n\n---\n\n## \u26a0\ufe0f **EARLY DEVELOPMENT - NOT PRODUCTION READY**\n\n> **WARNING:** This project is in **early alpha stage** and highly unstable. \n> \n> - \ud83d\udea7 **Breaking changes** may occur without notice\n> - \ud83d\udc1b **Bugs and incomplete features** are expected\n> - \u274c **NOT recommended for production use**\n> - \ud83d\udcdd **API may change significantly** between versions\n> \n> Use at your own risk! For production workloads, consider:\n> - [FastAPI](https://github.com/fastapi/fastapi) (original) with [Mangum](https://github.com/jordaneremieff/mangum)\n> - Wait for a stable 1.0.0 release of this project\n\n---\n\n## \ud83d\ude80 Why FastAPI-Lambda?\n\nFastAPI-Lambda is a lightweight, Lambda-optimized framework that maintains FastAPI's intuitive API while removing unnecessary dependencies and features incompatible with serverless environments.\n\n**Key Benefits:**\n- \u26a1 **<500ms cold starts** - No ASGI layer overhead\n- \ud83d\udd04 **Same FastAPI interfaces** - Minimal code changes required\n- \ud83d\udce6 **Lightweight** - Pydantic v2.7+ only (single dependency)\n- \ud83c\udfaf **Lambda-native** - Direct API Gateway event handling\n- \u2705 **Sync & Async** - Supports both `def` and `async def` endpoints\n\n## \ud83d\udcca Performance Comparison\n\n| Metric | Standard FastAPI | FastAPI-Lambda |\n|--------|-----------------|----------------|\n| Cold Start | 1-2s (with ASGI) | <500ms (direct) |\n| Package Size | ~5.8MB | ~3MB (48% reduction) |\n| Dependencies | Starlette + extras | Pydantic only |\n| Memory Overhead | ASGI + middleware | Minimal |\n\n## \ud83d\udce5 Installation\n\n```bash\npip install fastapi-lambda\n```\n\n## \ud83c\udfaf Quick Start\n\n```python\nfrom fastapi_lambda import FastAPI\n\napp = FastAPI()\n\n# Both sync and async endpoints work!\n@app.get(\"/\")\ndef root():\n return {\"message\": \"Hello from Lambda\"}\n\n@app.get(\"/async\")\nasync def async_endpoint():\n return {\"message\": \"Async works too!\"}\n\n# Lambda handler\nfrom fastapi_lambda import create_lambda_handler\nlambda_handler = create_lambda_handler(app)\n```\n\n## \ud83d\udd0c Deployment\n\n### Lambda Function URL\n```yaml\n# serverless.yml\nfunctions:\n api:\n handler: handler.lambda_handler\n url:\n cors: true\n```\n\n### API Gateway v1 (REST)\n```yaml\nfunctions:\n api:\n handler: handler.lambda_handler\n events:\n - http:\n path: \"/\"\n method: ANY\n - http:\n path: \"{proxy+}\"\n method: ANY\n```\n\n### API Gateway v2 (HTTP)\n```yaml\nfunctions:\n api:\n handler: handler.lambda_handler\n events:\n - httpApi:\n path: \"/{proxy+}\"\n method: \"*\"\n```\n\n## \u2705 Supported Features\n\n### HTTP REST API\n- \u2705 All methods: GET, POST, PUT, DELETE, PATCH, OPTIONS, HEAD\n- \u2705 Path/Query/Header parameters\n- \u2705 Request body validation\n- \u2705 Response models\n- \u2705 **Sync and async endpoints**\n\n### Validation & Serialization\n- \u2705 **Pydantic v2 only** (Rust-powered performance)\n- \u2705 Type-based validation\n- \u2705 JSON encoding/decoding\n\n### Dependency Injection\n- \u2705 `Depends()` with sync/async functions\n- \u2705 Generator-based cleanup (`yield`)\n- \u2705 Dependency caching\n- \u2705 Request/Response injection\n\n### OpenAPI Schema\n- \u2705 Automatic OpenAPI 3.1.0 schema generation\n- \u2705 JSON endpoint at `/openapi.json`\n- \u2705 Complete request/response documentation\n- \ud83d\udcdd Use external tools: Swagger Editor, Postman, Insomnia\n\n### Security\n- \u2705 HTTP Bearer (JWT tokens)\n- \u2705 Custom security schemes\n\n## \u274c Removed Features (Lambda Incompatible)\n\n| Feature | Why Removed | Alternative |\n|---------|-------------|-------------|\n| WebSockets | Lambda doesn't support persistent connections | Use AWS API Gateway WebSocket API separately |\n| Background Tasks | Lambda stops after response | Use SQS/EventBridge |\n| File Uploads | Payload size limits | Use S3 pre-signed URLs |\n| Streaming Responses | 6MB Lambda limit | Return URLs to S3 |\n| Swagger UI/ReDoc | Reduce package size | Use external tools with `/openapi.json` |\n\n## \ud83e\uddea Testing\n\n### Unit Tests\n```bash\n# Run all tests\nnpm run test\n\n# With coverage\nnpm run test:cov\n\n# Watch mode\nnpm run test:watch\n```\n\n### E2E Tests\n```bash\n# Setup (deploy to AWS)\nnpm run test:e2e:setup\n\n# Run E2E tests\nnpm run test:e2e\n```\n\nE2E tests automatically run against **all 3 deployment types**:\n- Lambda Function URL\n- API Gateway v1 (REST)\n- API Gateway v2 (HTTP)\n\nSee [tests/e2e/README.md](tests/e2e/README.md) for details.\n\n## \ud83d\udcd6 Documentation\n\n- [E2E Testing Guide](tests/e2e/README.md)\n- [Architecture & Design](.claude/CLAUDE.md)\n\n## \ud83e\udd1d Contributing\n\nContributions are welcome! 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