502 Bad Gateway - ResponseWithBody

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Symptom

The client application gets an HTTP status code of 502 Bad Gateway with the error code protocol.http.ResponseWithBody as a response for API calls.

Error message

Client application gets the following response code:

HTTP/1.1 502 Bad Gateway

In addition, you may observe one of the following error messages:

{
   "fault":{
      "faultstring":"Received 204 Response with message body",
      "detail":{
         "errorcode":"protocol.http.ResponseWithBody"
      }
   }
}

{
   "fault":{
      "faultstring":"Received 205 Response with message body",
      "detail":{
         "errorcode":"protocol.http.ResponseWithBody"
      }
   }
}

Possible causes

This error occurs if the HTTP response from the backend server to Apigee Edge is either 204 No Content or 205 Reset Content but it contains the response body and/or one or more of the following headers:

• Content-Length
• Content-Encoding
• Transfer-Encoding

As per the specifications RFC 7231, section 6.3.5: 204 No Content and RFC 7231, section 6.3.6: 205 Reset Content, it is expected that no additional content should be sent as part of the response payload body with status code 204 No Content or 205 Reset Content by the origin server. The response headers such as Content-Length, Content-Encoding or Transfer-Encoding indicate the size, type or format of the response payload.

Therefore, Apigee Edge returns a 502 Bad Gateway status code with the error code protocol.http.ResponseWithBody to the client under the following circumstances:

Here are the possible causes for this error:

Common diagnosis steps

Use one of the following tools/techniques to diagnose this error:

Cause: Response body or Headers with 204 response from backend server

Diagnosis

1. Determine the Fault Code and Fault Source for the error observed using API Monitoring, Trace tool, or NGINX access logs as explained in Common diagnosis steps.
2. If the Fault Code is protocol.http.ResponseWithBody and Fault Source has the value target, then this indicates that the backend server has responded with a 204 No Content or 205 Reset Content status code with the response body and/or one of the headers mentioned in Possible causes.

3. To validate if the backend server has indeed sent a response payload body and/or one or more of the headers mentioned in Possible causes, you can perform the following steps:

   1. If you are a Public Cloud user, and if you can make the same API request to the backend server directly from any of your systems.

   2. If you are a Private Cloud user, then you can make the same API request to the backend server directly from one of the Message Processors associated with the specific organization and environment where the failure is observed.

   3. Review the response received from the backend server and verify that it contains a response payload body and/or one or more of the above mentioned headers. If yes, then that’s the cause for this error.

      Sample #1

      Sample #1: Backend Server Response 204 with Content-Encoding Header

      curl -v "https://BACKEND_SERVER_HOST_NAME/PATH" -H "HEADER: VALUE" -X HTTP_REQUEST_METHOD
      

      …
      < HTTP/1.1 204 No Content
      < Content-Encoding: gzip
      < Date: Tue, 31 Jul 2021 21:41:13 GMT
      < Connection: keep-alive
      

      In this sample, the backend server responded with 204 No Content status code and Content-Encoding: gzip

      Sample #2

      Sample #2: Backend Server Response 204 with Content-Length Header

      curl -v "https://BACKEND_SERVER_HOST_NAME/PATH" -H "HEADER: VALUE" -X HTTP_REQUEST_METHOD
      

      …
      < HTTP/1.1 204 No Content
      < Content-Length: 48
      < Date: Tue, 31 Jul 2021 21:41:13 GMT
      < Connection: keep-alive
      

      In this sample, the backend server responded with 204 No Content status code and Content-Length: 48

      Sample #3

      Sample #3: Backend Server Response 205 with Response Body

      curl -v "https://BACKEND_SERVER_HOST_NAME/PATH" -H "HEADER: VALUE" -X HTTP_REQUEST_METHOD
      

      …
      < HTTP/1.1 205 Reset Content
      < Date: Sat, 31 Jul 2021 17:14:09 GMT
      < Content-Length: 12
      < Content-Type: text/plain; charset=utf-8
      <
      * Connection #0 to host X.X.X.X left intact
      This is a sample Response
      

      In this sample, the backend server responded with 205 Reset Content status code with response body This is a sample Response.

   4. In all of the above examples, the backend server sent 204 No Content or 205 Reset Content status code with the response body and/or one of the headers mentioned in Possible causes.
   5. Therefore, Apigee Edge sent 502 Bad Gateway status code with error code protocol.http.ResponseWithBody.

Resolution

Ensure that the backend server always adheres to the Specification RFC 7231, section 6.3.6: 205 Reset Content, when sending the 204 No Content or 205 Reset Content response to Apigee Edge. That is, the backend server MUST NOT send the following as part of a 204 No Content or 205 Reset Content response:

1. Response payload body
2. And any of the following headers:
   1. Content-Length
   2. Content-Encoding
   3. Transfer-Encoding

Specification

Apigee Edge responds with 502 Bad Gateway status code and the error code protocol.http.ResponseWithBody if the backend server sends a 204 No Content or 205 Reset Content response but does not adhere to the following RFC specifications:

Key points to note

The recommended solution is to fix the backend server to send the 204 No Content and 205 Reset Content status code without response body and any of the headers - Content-Length, Content-Encoding, and Transfer-Encoding and adhere to the specifications RFC 7231, section 6.3.5: 204 No Content and RFC 7231, section 6.3.6: 205 Reset Content.

If you still need any assistance from Apigee Support, go to Must gather diagnostic information.

Must gather diagnostic information

Gather the following diagnostic information, and then contact Apigee Edge Support:

If you are a Public Cloud user, provide the following information:

• Organization name
• Environment name
• API Proxy name
• Complete curl command used to reproduce the 502 error
• Trace file for the API requests

If you are a Private Cloud user, provide the following information:

• Complete error message observed for the failing requests
• Environment name
• API Proxy bundle
• Trace file for the API requests

• NGINX access logs /opt/apigee/var/log/edge-router/nginx/ORG~ENV.PORT#_access_log

  Where: ORG, ENV and PORT# are replaced with actual values.

• Message Processor system logs /opt/apigee/var/log/edge-message-processor/logs/system.log