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What is the Trace tool?

Trace is a tool for troubleshooting and monitoring API proxies running on Apigee Edge. Trace lets you probe the details of each step through an API proxy flow. 

How to use Trace

Trace is simple to use. You start a trace session, then make an API call to the Edge platform, and read the results.

  1. Select API Proxies from the APIs menu. 
  2. Select an API proxy from the API Proxies page.
  3. Be sure the API you wish to trace is deployed.
  4. Click Trace to go to the Trace tool view. 
  5. Use the Deployment to Trace dropdown menu to select which deployment environment and proxy revision you wish to trace. 
  6. Click Start Trace Session. When the Trace session is active, the API proxy records details of each step in the processing pipeline. While the Trace session is running, messages and contextual data are captured from live traffic.

  7. If you don't have any live traffic flowing through your proxy, then simply send a request to the API. You can use whatever tool you wish to send the request, such as cURL, the Edge API console, Postman, or any familiar tool. Or, you can send the request directly from the Trace tool itself. Just enter the URL and click Send

    Note: One Trace session can support 20 request/response transactions through the selected API proxy. Trace sessions automatically stop after 10 minutes if you don't manually stop it. 
     
  8. When you've captured a sufficient number of requests, click Stop Trace Session.
  9. A list of captured request/response transactions displays in the left menu. Click on any of the transactions to view detailed results.

How to read a trace

The trace tool has two main parts, the transaction map and the phase details:

  • The transaction map uses icons to mark each notable step that occurs during an API proxy transaction, including policy execution, conditional steps, and transitions. Hover over any icon to see summary information. The request flow steps appear along the top of the transaction map and response flow steps along the bottom.
  • The phase details section of the tool lists information about the proxy's internal processing, including variables that were set or read, request and response headers, and much more. Click any icon to see the phase details for that step.

Here's a sample trace tool map with the main proxy processing segments labeled:

Trace tool's transaction map

Transaction map legend

The following table describes the intent of the icons you will see in the transaction map. These icons mark each of the notable processing steps throughout the proxy flow.

Transaction map icons

  The client app that sends a request to the ProxyEndpoint of the API proxy. 
The circles mark transitional endpoints in the proxy flow. They are there when a request comes in from the client, when the request goes to the target, when the response comes back from the target, and when the response goes back to the client.

The tall bars indicate the beginning of a flow segment in the API proxy flow. Flow segments are: ProxyEndpoint request, TargetEndpoint request, TargetEndpoint response, and ProxyEndpoint response. A segment includes the PreFlow, Conditional Flows, and PostFlow. 

See Flows for more information. 

Indicates that Analytics actions have occurred in the background. 

A conditional flow that evaluates to true. For an introduction to conditional flows, see Flows.
A conditional flow that evaluates to false. For an introduction to conditional flows, see Flows.

 

Polices. Each type of policy has a unique icon. This one is for the AssignMessage policy. These icons let you see where policies are executed in the proper order and if they are successful or not. You can click a policy icon to see the results of its execution and if they are expected or not. For example, you can see if the message was transformed properly or if it is being cached. 

Properly executing policies are clearly indicated by check-marks. In the case of an error, a red exclamation mark is displayed on the icon.

Tip: Pay attention to the tooltip or the time line to see if any policy is taking longer than expected.

Appears when the backend target is a Node.js application. See Overview of Node.js on Apigee Edge.
The backend target called by the API proxy.
The time line indicates how long (in milliseconds) that the processing time took to complete. Comparing the elapsed time segments helps you isolate the policies that are taking the longest to execute that are slowing down your API calls.
The Epsilon indicates a time-span smaller than a millisecond.

Disabled. Appears on a policy icon when a policy is disabled. A policy can be disabled with the public API. See API proxy configuration reference.

Error. Appears on a policy icon when the Policy Step condition evaluates to false (see Flow variables and conditions), or on the RaiseFault policy icon whenever a RaiseFault policy executes.
Skipped. Appears on a policy icon when the policy was not executed because the step condition evaluated to false. See Flow variables and conditions for more information. 

Understanding the phase details

The Phase Details part of the tool tells you a lot about the state of your proxy at each processing step. Here are some of the details provided in the Phase Details. Click any icon in the trace tool to see details for the selected step, or use the Next/Back buttons to move from one step to another. 

Trace captures message content. If your message payloads contain sensitive information, then you should enable data masking. For instructions, see Data masking.

Phase Detail Description
Proxy Endpoint Indicates which ProxyEndpoint flow was selected for execution. An API proxy can have multiple named proxy endpoints. 
Request Headers Lists the HTTP request headers.
Request Content Shows the HTTP request body.
Properties Properties represent the internal state of the API proxy. These are not shown by default.
Variables Read Lists the flow variables that were read by a policy. See also Introduction to flow variables.
Variables Read and Assigned Lists the flow variables that were read and assigned a value by a policy.
Target Endpoint Indicates which TargetEndpoint was selected for execution. 
Response Headers Lists the HTTP response headers.
Response Content Shows the HTTP response body. 
PostClientFlow Shows information about the PostClientFlow, which executes after the request is returned to the requesting client app. Only MessageLogging policies can be attached to the PostClientFlow. The PostClientFlow is currently used primarily for measuring the time interval between the start and end timestamps for the response message.

Debugging with Trace

Trace lets you see a lot of internal details about an API proxy. For example:

  • You can see at a glance which policies are executing correctly or failing. 
  • Let's say you noticed through one of the Analytics dashboards that one of your APIs is experiencing an unusual decrease in performance. Now, you can use Trace to help identify where the bottleneck is occurring. Trace gives the time, in milliseconds, that it takes for each processing step to complete. If you find one step is taking too long, you can take corrective action. 
  • By looking at the phase details, you can check headers that are being sent to the backend, view variables set by policies, and so on.
  • By verifying the base path, you can ensure that a policy is routing the message to correct server.

Selecting View Options

Choose the view options for the trace session.


 

Option Description
Show Disabled Policies Show any disabled policies. A policy can be disabled with the public API. See API proxy configuration reference.
Show Skipped Phases Show any phases that were skipped. A skipped phase occurs when policy was not executed because the step condition evaluated to false. See Flow variables and conditions for more information. 
Show all FlowInfos Represent transitions within a flow segment.
Automatically Compare Selected Phase Compares the selected phase to the previous one. Turn this off to see only the selected phase.
Show Variables Show or hide variables that were read and/or assigned a value.
Show Properties Properties represent the internal state of the API proxy. (Hidden by default.)

Downloading trace results

You can download an XML file of the trace results for viewing offline. The file shows the complete details of the listening session including the contents of all headers, variables and policies.

To download raw trace output, click Download Trace Session.

 

Help or comments?

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