Lambda Server

A stateless Python MCP server packaged as a custom AWS Lambda container image and exposed through an API Gateway HTTP API. It uses MCP Streamable HTTP at /mcp.

Included tools

• hello(name) — returns a greeting
• add(a, b) — adds two numbers
• current_time() — returns the current UTC time

Add your own functions in src/server.py and decorate them with @mcp.tool().

Prerequisites

• Docker
• AWS CLI authenticated to your AWS account

Test the Python tools

py -3.12 -m venv .venv
.venv\Scripts\Activate.ps1
pip install -r requirements-dev.txt
pytest

Build the Lambda image

Lambda is configured for ARM64 by default in these examples:

docker buildx build --platform linux/arm64 --provenance=false -t lambda-mcp-server:latest --load .

For an x86_64 Lambda, use --platform linux/amd64 instead.

Test the container locally

Start the Lambda runtime emulator included in the AWS base image:

docker run --platform linux/arm64 --rm -p 9000:8080 lambda-mcp-server:latest

Invoke it from another terminal with an API Gateway HTTP API v2 event:

$body = '{"jsonrpc":"2.0","id":1,"method":"tools/list","params":{}}'
$event = @{
  version = "2.0"
  routeKey = "POST /mcp"
  rawPath = "/mcp"
  rawQueryString = ""
  headers = @{ "content-type" = "application/json"; "accept" = "application/json, text/event-stream" }
  requestContext = @{ http = @{ method = "POST"; path = "/mcp"; protocol = "HTTP/1.1"; sourceIp = "127.0.0.1"; userAgent = "local" }; requestId = "local"; routeKey = "POST /mcp"; stage = '$default'; time = ""; timeEpoch = 0 }
  body = $body
  isBase64Encoded = $false
} | ConvertTo-Json -Depth 10 -Compress
Invoke-RestMethod -Method Post -Uri http://localhost:9000/2015-03-31/functions/function/invocations -ContentType application/json -Body $event

Push to Amazon ECR

Replace the variables with your AWS account details:

$Region = "ap-south-1"
$AccountId = aws sts get-caller-identity --query Account --output text
$Repository = "lambda-mcp-server"

aws ecr create-repository --repository-name $Repository --region $Region
aws ecr get-login-password --region $Region | docker login --username AWS --password-stdin "$AccountId.dkr.ecr.$Region.amazonaws.com"
docker tag "lambda-mcp-server:latest" "$AccountId.dkr.ecr.$Region.amazonaws.com/${Repository}:latest"
docker push "$AccountId.dkr.ecr.$Region.amazonaws.com/${Repository}:latest"

Create or update a Lambda function using that image URI. Set its architecture to arm64, timeout to 30 seconds, and memory to at least 512 MB.

API Gateway

Create an API Gateway HTTP API with Lambda proxy integration. Add an ANY /mcp route targeting the Lambda function, then grant API Gateway permission to invoke it. The MCP URL will look like:

https://YOUR_API_ID.execute-api.ap-south-1.amazonaws.com/mcp

Connect through AgentCore Gateway

Keep the Lambda image command as src.server.handler and expose the function through the API Gateway ANY /mcp route described above.

In Amazon Bedrock AgentCore Gateway, add an MCP server target using the full API Gateway endpoint:

https://YOUR_API_ID.execute-api.ap-south-1.amazonaws.com/mcp

Use DEFAULT listing mode so AgentCore synchronizes the tools exposed by FastMCP. No separate tool-schema JSON is needed because AgentCore discovers the tools through MCP tools/list.

For initial testing you can use no outbound authorization. For production, configure IAM authorization on API Gateway and select IAM (SigV4) outbound authorization for the AgentCore target.

Connect an MCP client

Configure a client that supports Streamable HTTP with the deployed output URL:

{
  "mcpServers": {
    "lambda-tools": {
      "url": "https://YOUR_API_ID.execute-api.ap-south-1.amazonaws.com/mcp"
    }
  }
}

Production note

An unauthenticated API Gateway route is public. Before exposing tools that access private data or perform writes, add authentication at API Gateway (for example JWT/Cognito) and validate authorization in the application. Keep tools stateless, or store shared state in an external service such as DynamoDB.