API Gateway HTTP API with VPC Link to ECS Service Returns "Internal Server Error"

Issue Description

I'm trying to set up an API Gateway HTTP API with VPC Link to connect directly to an ECS service using CloudMap service discovery (without an NLB), following the architecture described in this AWS blog post .

When I access my ECS service directly via its private IP (10.0.4.92), it returns a successful response:

curl http://10.0.4.92

{"success":true,"data":"Hello World!","meta":{"timestamp":"2025-07-10T15:18:51.855Z","path":"/","duration":1}}

However, when I try to access it through the API Gateway endpoint, I get an "Internal Server Error":

curl https://s47d139oy9.execute-api.ca-central-1.amazonaws.com/

{"message":"Internal Server Error"}

My Setup

• API Gateway HTTP API (ID: s47d139oy9)
• VPC Link (ID: v11emi)
• CloudMap service (ARN: arn:aws:servicediscovery:ca-central-1:555907822687:service/srv-jtxdxjqpkygbiffi)
• ECS service running on port 80 (accessible directly via private IP)

What I've Tried

1. Created an integration with the CloudMap service ARN:

aws apigatewayv2 create-integration \
  --api-id s47d139oy9 \
  --integration-type HTTP_PROXY \
  --integration-method ANY \
  --connection-type VPC_LINK \
  --connection-id v11emi \
  --payload-format-version 1.0 \
  --integration-uri arn:aws:servicediscovery:ca-central-1:555907822687:service/srv-jtxdxjqpkygbiffi \
  --region ca-central-1

1. Created routes with different paths:

aws apigatewayv2 create-route \
  --api-id s47d139oy9 \
  --route-key 'ANY /' \
  --target "integrations/7hhjg48" \
  --region ca-central-1

1. Deployed the API:

aws apigatewayv2 create-deployment \
  --api-id s47d139oy9 \
  --stage-name '$default' \
  --region ca-central-1

1. Tried different path configurations (/, /test, /{proxy+})
2. Verified that the ECS service responds correctly when accessed directly
3. Checked security groups to ensure they allow traffic between components
4. Enabled access logs but couldn't find detailed error information

What I Don't Want to Do

I specifically don't want to use a Network Load Balancer (NLB) between the API Gateway and ECS service. I want to follow the architecture in the blog post that uses CloudMap service discovery directly.

Questions

1. What could be causing the "Internal Server Error" when the ECS service works fine when accessed directly?
2. Are there any specific configurations or settings I'm missing for the API Gateway HTTP API with VPC Link and CloudMap service discovery?
3. How can I get more detailed error information from the API Gateway HTTP API to troubleshoot this issue?
4. Is there a working example of this architecture that I can reference?

Any help or guidance would be greatly appreciated!