OpenAPI MCP Server - AWS Lambda Deployment

Serverless deployment of the AWS Labs OpenAPI MCP Server on AWS Lambda with API Gateway.

Overview

This project wraps the awslabs openapi-mcp-server to run as a serverless Lambda function, enabling MCP (Model Context Protocol) clients to interact with OpenAPI-defined APIs through AWS infrastructure.

Architecture

• Lambda Function: FastMCP server with HTTP transport (Starlette ASGI)

• API Gateway: HTTP API exposing the MCP endpoints

• Transport: Mangum ASGI adapter (no child process overhead)

Prerequisites

• Python 3.12+

• uv package manager

• AWS CLI configured

• AWS CDK CLI: npm install -g aws-cdk

Local Setup

Install dependencies:

uv sync

Deployment

1. Bootstrap CDK (first time only)

cdk bootstrap

2. Deploy Stack

cd cdk
cdk deploy \
  --parameters ApiName=MyAPI \
  --parameters ApiBaseUrl=https://api.example.com \
  --parameters ApiSpecUrl=https://api.example.com/openapi.json \
  --parameters AuthType=none

Configuration Parameters

• ApiName: Display name for the API

• ApiBaseUrl: Base URL of the target API

• ApiSpecUrl: URL to the OpenAPI specification (JSON or YAML)

• AuthType: Authentication method (none, basic, bearer, api_key, cognito)

Additional Auth Configuration

Set environment variables in cdk/openapi_mcp_stack.py for authentication:

Basic Auth:

• AUTH_USERNAME

• AUTH_PASSWORD

Bearer Token:

• AUTH_TOKEN

API Key:

• AUTH_API_KEY

• AUTH_API_KEY_NAME

• AUTH_API_KEY_IN (header/query/cookie)

Cognito:

• AUTH_COGNITO_CLIENT_ID

• AUTH_COGNITO_USERNAME

• AUTH_COGNITO_PASSWORD

• AUTH_COGNITO_USER_POOL_ID

• AUTH_COGNITO_REGION

3. Get API URL

After deployment, CDK outputs the API Gateway URL:

# Output example:
# OpenApiMcpStack.ApiUrl = https://abc123.execute-api.us-east-1.amazonaws.com/

Testing

Test the deployed Lambda function:

curl -X POST https://<api-url>/message \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc": "2.0", "method": "tools/list", "id": 1}'

Performance Considerations

• Cold Start: ~1-2 seconds (initializes MCP server + loads OpenAPI spec)

• Warm Start: ~100-300ms (reuses server instance)

• Timeout: 30 seconds (configurable in stack)

• Memory: 512 MB (configurable in stack)

Cost Optimization

• Requests: Pay per invocation

• Memory/Duration: 512 MB x execution time

• API Gateway: HTTP API (cheaper than REST API)

Development

Run MCP server locally:

uv run awslabs.openapi-mcp-server \
  --api-name MyAPI \
  --api-url https://api.example.com \
  --spec-url https://api.example.com/openapi.json

Cleanup

cd cdk
cdk destroy

License

This project includes code from awslabs/mcp licensed under Apache-2.0. See LICENSE and NOTICE files.