Fix: Empty MCP Config In AWS Bedrock AgentCore Gateway

Nov 30, 2025 by Alex Johnson 55 views

AWS Bedrock AgentCore Alpha: Troubleshooting Empty MCP Configuration in CloudFormation

Experiencing issues with your AWS Bedrock AgentCore Alpha deployments? Specifically, are you encountering an empty configuration for your MCP (Managed Compute Platform) Server Gateway Target within CloudFormation? If so, you're not alone. This article delves into a common bug encountered when using the aws-bedrock-agentcore-alpha CDK library, explains the root cause, and provides potential solutions and workarounds. Let's get your deployments back on track!

Understanding the Bug: Empty TargetConfiguration for MCP Servers

The core problem lies in how the CloudFormation template is generated when creating a Gateway Target for an MCP Server. Whether you're utilizing gateway.addMcpServerTarget() or GatewayTarget.forMcpServer(), the resulting CloudFormation synthesis can produce an empty TargetConfiguration.Mcp: {} object. This is a critical issue because it prevents the inclusion of the necessary endpoint configuration, leading to deployment failures.

The Technical Details

The McpServerTargetConfiguration.renderMcpConfiguration() method is designed to return a configuration object containing the MCP server endpoint: { mcpServer: { endpoint: this.endpoint } }. However, this endpoint information is not being correctly incorporated into the final CloudFormation template. This discrepancy results in a validation error during deployment, as CloudFormation expects a complete configuration, including the endpoint, to properly establish the gateway target.

Regression Status

It's important to note that this issue is identified within the alpha stage of the aws-bedrock-agentcore library. This means it's a relatively new feature, and such issues are not uncommon during early development phases. There is no known working version, as this bug appears to be present from the initial introduction of the MCP Server Gateway Target functionality.

Decoding the Error Messages

The error messages you might encounter in CloudFormation can be quite verbose, but they provide valuable clues. A typical error message related to this bug looks like this:

Properties validation failed for resource GatewayWeatherMcpServer with message:
#/TargetConfiguration: #: 0 subschemas matched instead of one
#/TargetConfiguration/Mcp: #: 0 subschemas matched instead of one
#/TargetConfiguration/Mcp: required key [OpenApiSchema] not found
#/TargetConfiguration/Mcp: required key [SmithyModel] not found
#/TargetConfiguration/Mcp: required key [Lambda] not found
#/TargetConfiguration/Mcp: required key [McpServer] not found

This error essentially indicates that the TargetConfiguration for the MCP server is incomplete. It's missing essential components like OpenApiSchema, SmithyModel, Lambda, and most importantly, McpServer. This absence of McpServer confirms that the endpoint configuration is not being included.

Reproducing the Bug: A Step-by-Step Guide

To better understand the issue and potentially test solutions, reproducing the bug is essential. Here's a TypeScript code snippet that demonstrates how to reproduce the empty MCP configuration problem:

import * as agentcore from '@aws-cdk/aws-bedrock-agentcore-alpha';
import * as cdk from 'aws-cdk-lib';
import { Construct } from 'constructs';

export class TestStack extends cdk.Stack {
  constructor(scope: Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    // Create a Gateway
    const gateway = new agentcore.Gateway(this, 'Gateway', {
      gatewayName: 'test-gateway',
    });

    // Attempt to add MCP Server target
    gateway.addMcpServerTarget('McpServer', {
      gatewayTargetName: 'test-mcp-server',
      description: 'Test MCP Server',
      endpoint: 'https://bedrock-agentcore.us-east-1.amazonaws.com/runtimes/arn%3Aaws%3Abedrock-agentcore%3Aus-east-1%3A123456789012%3Aagent-runtime%2FTEST/invocations?qualifier=DEFAULT',
      credentialProviderConfigurations: [
        agentcore.GatewayCredentialProvider.fromIamRole(),
      ],
    });
  }
}

// Run: cdk synth
// Observe: TargetConfiguration.Mcp is empty {}
// Run: cdk deploy
// Observe: CloudFormation validation error

Walking Through the Code

Import necessary modules: The code begins by importing the required modules from aws-cdk-lib and @aws-cdk/aws-bedrock-agentcore-alpha.
Define the stack: A new CDK stack named TestStack is created, extending cdk.Stack. This stack will contain the resources we want to deploy.
Create a Gateway: Within the stack's constructor, a Gateway resource is created using new agentcore.Gateway(). This represents the entry point for our agent.
Add MCP Server Target: The core of the issue lies in this step. gateway.addMcpServerTarget() is used to add an MCP server target to the gateway. We provide a target name, description, an example endpoint, and a credential provider configuration using agentcore.GatewayCredentialProvider.fromIamRole().
Synthesize and Deploy: The comments in the code highlight the crucial steps: cdk synth to synthesize the CloudFormation template and cdk deploy to attempt deployment. The expected outcome is an empty TargetConfiguration.Mcp in the synthesized template and a CloudFormation validation error during deployment.

By running cdk synth, you can examine the generated CloudFormation template and confirm the empty TargetConfiguration.Mcp object. Attempting cdk deploy will then trigger the validation error, solidifying the presence of the bug.

Pinpointing the Root Cause and Potential Solutions

The investigation suggests that the problem lies in how the McpServerTargetConfiguration._render() method or the CloudFormation property mapping handles the MCP server configuration. While renderMcpConfiguration() correctly returns the expected object { mcpServer: { endpoint: this.endpoint } }, this structure isn't being accurately translated into the CloudFormation template.

Potential Causes

Case Sensitivity: The CloudFormation property name might be expecting McpServer (capital 'S') instead of mcpServer (lowercase 's').
Property Mapping Issue: There might be a flaw in the property mapping within the L1 (low-level) construct responsible for generating the CloudFormation resource.

Suggested Fixes

Verify CloudFormation Property Mapping: Carefully examine the CfnGatewayTarget resource and its property mappings for the MCP target configuration type. Ensure that the property names and data structures align with CloudFormation's expectations.
Check Serialization Logic: Investigate the serialization logic within McpServerTargetConfiguration._render() to guarantee that the output is correctly formatted for CloudFormation.

Workaround: A Temporary Solution

While a permanent fix is being developed, a workaround exists to bypass the issue. Instead of using the Gateway, you can directly connect your Agent to the MCP Server Runtime ARN. This approach circumvents the problematic Gateway Target configuration.

Important Note: This workaround might not be suitable for all scenarios, as it bypasses the benefits provided by the Gateway, such as centralized routing and security policies. However, it can be a viable temporary solution to get your deployments working.

Staying Updated and Contributing

The aws-bedrock-agentcore-alpha library is under active development, and issues like this are expected during the alpha phase. To stay informed about progress and fixes:

Monitor GitHub Issues: Keep an eye on the GitHub repository for the aws-cdk project. Look for existing issues related to aws-bedrock-agentcore-alpha and this specific bug. You can subscribe to the issue to receive updates.
Engage in Discussions: Participate in discussions within the GitHub issue or other relevant forums. Sharing your experiences and insights can help the development team understand the problem better and expedite the solution.
Contribute (if possible): If you have the expertise, consider contributing to the fix. You can submit a pull request with a proposed solution, following the project's contribution guidelines.

Conclusion: A Path Forward

The empty MCP configuration bug in the aws-bedrock-agentcore-alpha library is a known issue that prevents proper deployment of Gateway Targets for MCP Servers. By understanding the problem, reproducing the bug, and exploring potential solutions and workarounds, you can navigate this challenge effectively.

Remember to stay updated on the progress of the fix and engage with the community to contribute to a more robust and reliable aws-bedrock-agentcore-alpha library. For more in-depth information on AWS Bedrock and its capabilities, consider exploring the official AWS Bedrock Documentation. 🚀