Debug APIs with Request Tracing in APIM

Debugging APIs using Request Tracing in Azure API Management is a powerful way to diagnose and troubleshoot issues with your APIs. Request tracing allows you to capture detailed information about incoming requests, outgoing responses, and the processing steps in between. This is especially useful when you need to identify where something went wrong in your API workflow.

Here’s a basic explanation of how to use request tracing in Azure API Management:

Steps to Debug APIs Using Request Tracing

1. Enable Request Tracing:
   • Go to the Azure Portal and navigate to your API Management Service.
   • Select the APIs section and choose the specific API you want to debug.
   • In the API settings, enable Diagnostics and configure logging to capture traces. You can send logs to Azure Monitor, Application Insights, or a storage account.
2. Add the Ocp-Apim-Trace Header:
   • To trigger request tracing for a specific API call, you need to include the Ocp-Apim-Trace: true header in your HTTP request.
   • This header tells Azure API Management to capture detailed trace information for that specific request.

   Example of a request with tracing enabled:

   GET https://<your-api-management-service>.azure-api.net/<api-endpoint>
   Ocp-Apim-Trace: true
   Authorization: Bearer <your-token>

3. Review the Trace Information:
   • After making the request, the response will include a special header called Ocp-Apim-Trace-Location.
   • This header contains a URL where you can download the detailed trace log.

   Example of the response header:

   Ocp-Apim-Trace-Location: https://<your-api-management-service>.azure-api.net/inspector/<trace-id>

4. Analyze the Trace Log:
   • Open the URL provided in the Ocp-Apim-Trace-Location header in your browser or use a tool like Postman to download the trace log.
   • The trace log contains detailed information about:
     • The incoming request (headers, body, etc.).
     • The policies applied (e.g., rate limiting, transformation, etc.).
     • The backend request sent to your API.
     • The backend response received.
     • The final response sent back to the client.
5. Identify and Fix Issues:
   • Use the trace log to identify where the issue occurred. For example:
     • If a policy is modifying the request incorrectly, you’ll see the changes in the trace.
     • If the backend is returning an error, you’ll see the exact response from the backend.
     • If there’s a mismatch between the expected and actual request/response, you can pinpoint the problem.

Example Scenario

Let’s say you have an API that transforms a JSON request and forwards it to a backend service. However, the backend is returning a 400 Bad Request error.

1. Enable tracing by adding the Ocp-Apim-Trace: true header to your request.
2. Make the API call and check the Ocp-Apim-Trace-Location header in the response.
3. Download the trace log and analyze it:
   • Check if the incoming request is correct.
   • Verify if the transformation policy is modifying the request as expected.
   • Look at the backend request to see if it matches what the backend expects.
   • Check the backend response to understand why it’s returning a 400 error.

Key Benefits of Request Tracing

• Detailed Insights: You get a step-by-step breakdown of how the request is processed.
• Policy Debugging: You can see how each policy (e.g., rate limiting, transformation) affects the request and response.
• Backend Debugging: You can inspect the exact request sent to the backend and the response received.
• Quick Issue Identification: Helps you quickly identify where the problem lies (e.g., in the API Management policies or the backend service).

Limitations

• Request tracing is only available for individual requests (not for bulk or continuous tracing).
• Trace logs are temporary and must be downloaded immediately after the request.