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Summary
This article explains how to troubleshoot a SOAP-based API that returns HTTP 404 and HTTP 500 errors in Azure API Management.
This article is the second scenario of the Azure API Management troubleshooting series lab. Ensure you follow the lab setup instructions as per the API Management troubleshooting series lab instructions.
Original product version: API Management Service
Original KB number: 4464934
Symptoms
The Calculator API found at http://www.dneonline.com/calculator.asmx performs four operations: Add, Subtract, Multiply, and Divide, based on two input parameters: intA and intB. This API uses an ASMX file-based service that uses Simple Object Access Protocol (SOAP) 1.1 protocol so the input parameters are passed in the SOAP envelope body.
In this scenario, the Add and Subtract operations work as expected, but you encounter HTTP 404 errors while performing a Multiply operation and HTTP 500 errors when performing a Divide operation.
The expected output of a Multiply operation should be something like the following example:
<?xml version="1.0" encoding="UTF-8"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<soap:Body>
<MultiplyResponse xmlns="http://tempuri.org/">
<MultiplyResult>int</MultiplyResult>
</MultiplyResponse>
</soap:Body>
</soap:Envelope>
The expected output of a Divide operation should be something like the following example:
<?xml version="1.0" encoding="UTF-8"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<soap:Body>
<DivideResponse xmlns="http://tempuri.org/">
<DivideResult>int</DivideResult>
</DivideResponse>
</soap:Body>
</soap:Envelope>
Troubleshooting
To determine what causes the HTTP 404 and HTTP 500 responses (whether it's API Management or the backend SOAP API), collect an API Management inspector trace to inspect the request and response.
If multiple operations cause HTTP 404 or HTTP 500 errors, it indicates that the origin server can't find a current representation for the target resource or isn't able to disclose that one exists.
When you examine the backend section of an API Management inspector trace, the same observation is evident from the message as shown in the following example:
{
"backend": [
{
"source": "configuration",
"timestamp": "2018-07-29T12:30:08.3500317Z",
"elapsed": "00:00:00.7276962",
"data": {
"message": "Unable to identify Api or Operation for this request. Responding to the caller with 404 Resource Not Found."
}
}
]
}
You need to first examine the request URL and headers sent from API Management to the backend API from Test and compare them with a sample of SOAP request for the Multiply operation you performed at http://www.dneonline.com/calculator.asmx.
Request headers from an API Management inspector trace look something like the following example:
{
"data": {
"request": {
"method": "POST",
"url": "https://pratyay.azure-api.net/calc",
"headers": [
{
"name": "Ocp-Apim-Subscription-Key",
"value": "34ae22db7f2c4c5da7b74a55adf03223"
},
{
"name": "X-Forwarded-For",
"value": "223.226.79.35"
},
{
"name": "Cache-Control",
"value": "no-cache"
},
{
"name": "Connection",
"value": "Keep-Alive"
},
{
"name": "Content-Length",
"value": "292"
},
{
"name": "Content-Type",
"value": "application/soap+xml; action=http://tempuri.org/Multiply"
},
{
"name": "Accept",
"value": "*/*"
},
{
"name": "Accept-Encoding",
"value": "gzip,deflate,br"
},
{
"name": "Accept-Language",
"value": "en-US,en;q=0.5"
},
{
"name": "Host",
"value": "pratyay.azure-api.net"
},
{
"name": "Referer",
"value": "https://apimanagement.hosting.portal.azure.net/apimanagement/Content/1.0.385.3/apimap/apimap-apis/index.html?locale=en&trustedAuthority=https://ms.portal.azure.com"
}
]
}
}
}
The SOAP 1.1 request needs a request header SOAPAction that's missing in the initial request sent from API Management as shown in the following example:
Host: www.dneonline.com
Content-Type: text/xml; charset=utf-8
Content-Length: length
SOAPAction: "http://tempuri.org/Multiply"
Adding the SOAPAction header with the value http://tempuri.org/Multiply resolves the problem. Add the request header under the Frontend definition of the Multiply operation, and then set the value as a default value in the Headers tab. You no longer need to send that header value for each request.
A Divide operation causing HTTP 500 (Internal Server Error) errors indicates the server encountered an unexpected condition that prevented it from fulfilling the request. This condition means the backend service can't process your request body sent from API Management.
You can now examine the request body sent from API Management. The denominator (intB) is set to zero which leads to an unhandled exception. This condition is the cause of the HTTP 500 (Internal Server Error).
The following example shows the request body sent from API Management inspector trace for a Divide operation:
POST calc HTTP/1.1
Host: pratyay.azure-api.net
SOAPAction: http://tempuri.org/Divide
Cache-Control: no-cache
Ocp-Apim-Trace: true
Content-Type: application/soap+xml; action=http://tempuri.org/Divide
Ocp-Apim-Subscription-Key: ********************************
<?xml version="1.0" encoding="utf-8"?>
<Envelope xmlns="http://www.w3.org/2003/05/soap-envelope">
<Body>
<Divide xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://tempuri.org/">
<intA>1</intA>
<intB>0</intB>
</Divide>
</Body>
</Envelope>
When you check the request content representation from the Request tab present in the Frontend definition of the Divide operation, you can see that the intB value is set to zero. Change the value of intB to a non-zero value. This change should resolve the issue.
