Clarification on Shadowing and Return Error Configuration in Krakend

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ejie tung

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Jan 24, 2025, 9:03:30 AMJan 24

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Hi, I have a question and would like to confirm a few details about implementing shadowing in Krakend.

Currently, I am implementing shadowing for specific endpoints in my configuration. Most of my endpoints use the no-op encoding, but I noticed that I cannot use it when implementing shadowing. For now, shadowing works well in the "happy case" scenarios for the designated endpoints.

After deploying this setup to production, we encountered an issue: the behavior of the return status codes and response bodies is different between no-op and json encodings during error scenarios. Specifically, when clients send an invalid payload, they do not receive a proper response body (status code and message) when no-op is used.

I reviewed the documentation and reproduced the issue in my local environment using Docker Compose. I managed to fix the issue locally by applying the following global router configuration:

- Works as expected in local

{
  "version": 3,
  "name": "My API Gateway with Shadowing",
  "port": 8080,
  "extra_config": {
    "router": {
      "return_error_msg": true
    }
  },
  "endpoints": [
    {
      "endpoint": "/error",
      "method": "GET",
      "output_encoding": "json",

      "backend": [
        {
          "host": [
            "http://data-service-gcp:5000"
          ],
          "url_pattern": "/error",
          "extra_config": {
            "backend/http": {
              "return_error_code": true
            }
          }
        },
        {
          "host": [
            "http://data-service-aws:5000"
          ],
          "url_pattern": "/error",
          "extra_config": {
            "backend/http": {
              "return_error_code": true
            },
            "proxy": {
              "shadow": true
            }
          }
        }
      ]
    },
}

- Works as expected for "2XX" respond from backend, but 500 for non 2XX

{
  "version": 3,
  "name": "My API Gateway with Shadowing",
  "port": 8080,
  "endpoints": [
    {
      "endpoint": "/data/{data_id}",
      "method": "GET",
      "output_encoding": "json",
      "backend": [
        {
          "host": [
            "http://data-service-v1:5000"
          ],
          "url_pattern": "/data/{data_id}"
        },
        {
          "host": [
            "http://data-service-v2:5000"
          ],
          "url_pattern": "/data/{data_id}",
          "extra_config": {
            "proxy": {
              "shadow": true
            }
          }
        }
      ]
    },
}

While the fix works in the local environment, I’m a bit concerned about applying this change in production, as it affects the global router configuration. Specifically, I want to ensure that this update will not inadvertently affect other endpoints in my gateway, as I am only implementing shadowing for a single endpoint.

Anyone can confirm whether this change is isolated to shadowing-related endpoints or if it might impact other routes as well? - if there are some docs, can also share, currently i cannot find any.