View X-Ray traces in Step Functions - Amazon Step Functions
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View X-Ray traces in Step Functions

In this tutorial, you will learn how to use X-Ray to trace errors that occur when running a state machine. You can use Amazon X-Ray to visualize the components of your state machine, identify performance bottlenecks, and troubleshoot requests that resulted in an error. In this tutorial, you will create several Lambda functions that randomly produce errors, which you can then trace and analyze using X-Ray.

The Creating a Step Functions State Machine That Uses Lambda tutorial walks you though creating a state machine that calls a Lambda function. If you have completed that tutorial, skip to Step 2 and use the Amazon Identity and Access Management (IAM) role that you previously created.

Step 1: Create an IAM Role for Lambda

Both Amazon Lambda and Amazon Step Functions can execute code and access Amazon resources (for example, data stored in Amazon S3 buckets). To maintain security, you must grant Lambda and Step Functions access to these resources.

Lambda requires you to assign an Amazon Identity and Access Management (IAM) role when you create a Lambda function, in the same way Step Functions requires you to assign an IAM role when you create a state machine.

You use the IAM console to create a service-linked role.

To create a role (console)

  1. Sign in to the Amazon Web Services Management Console and open the IAM console at https://console.amazonaws.cn/iam/.

  2. In the navigation pane of the IAM console, choose Roles. Then choose Create role.

  3. Choose the Amazon Service role type, and then choose Lambda.

  4. Choose the Lambda use case. Use cases are defined by the service to include the trust policy required by the service. Then choose Next: Permissions.

  5. Choose one or more permissions policies to attach to the role (for example, AWSLambdaBasicExecutionRole). See Amazon Lambda Permissions Model.

    Select the box next to the policy that assigns the permissions that you want the role to have, and then choose Next: Review.

  6. Enter a Role name.

  7. (Optional) For Role description, edit the description for the new service-linked role.

  8. Review the role, and then choose Create role.

Step 2: Create a Lambda Function

Your Lambda function will randomly throw errors or time out, producing example data to view in X-Ray.

Important

Ensure that your Lambda function is under the same Amazon account and Amazon Region as your state machine.

  1. Open the Lambda console and choose Create function.

  2. In the Create function section, choose Author from scratch.

  3. In the Basic information section, configure your Lambda function:

    1. For Function name, enter TestFunction1.

    2. For Runtime, choose Node.js 12.x.

    3. For Role, select Choose an existing role.

    4. For Existing role, select the Lambda role that you created earlier.

      Note

      If the IAM role that you created doesn't appear in the list, the role might still need a few minutes to propagate to Lambda.

    5. Choose Create function.

      When your Lambda function is created, note its Amazon Resource Name (ARN) in the upper-right corner of the page. For example:

      arn:aws-cn:lambda:us-east-1:123456789012:function:TestFunction1
  4. Copy the following code for the Lambda function into the Function code section of the TestFunction1 page.

    function getRandomSeconds(max) { return Math.floor(Math.random() * Math.floor(max)) * 1000; } function sleep(ms) { return new Promise(resolve => setTimeout(resolve, ms)); } exports.handler = async (event, context) => { if(getRandomSeconds(4) === 0) { throw new Error("Something went wrong!"); } let wait_time = getRandomSeconds(5); await sleep(wait_time); return { 'response': true } };

    This code creates randomly timed failures, which will be used to generate example errors in your state machine that can be viewed and analyzed using X-Ray traces.

  5. Choose Save.

Step 3: Create two more Lambda functions

Create two more Lambda functions.

  1. Repeat Step 2 to create two more Lambda functions. For the next function, in Function name, enter TestFunction2. For the last function, in Function name, enter TestFunction3.

  2. In the Lambda console, check that you now have three Lambda functions, TestFunction1, TestFunction2, and TestFunction3.

Step 4: Create a State Machine

Use the Step Functions console to create a state machine with three Task states. Each Task state will a reference one of your three Lambda functions.

  1. Open the Step Functions console and choose Create a state machine.

  2. On the Define state machine page, choose Author with code snippets. For Type, choose Standard.

    Note

    State machine, execution, and activity names must be 1–80 characters in length, must be unique for your account and Amazon Region, and must not contain any of the following:

    • Whitespace

    • Wildcard characters (? *)

    • Bracket characters (< > { } [ ])

    • Special characters (: ; , \ | ^ ~ $ # % & ` ")

    • Control characters (\\u0000 - \\u001f or \\u007f - \\u009f).

    Step Functions allows you to create state machine, execution, and activity names that contain non-ASCII characters. These non-ASCII names don't work with Amazon CloudWatch. To ensure that you can track CloudWatch metrics, choose a name that uses only ASCII characters.

  3. In the State machine definition pane, replace the example with the following state machine definition. For each Task task state, use the ARN of the corresponding Lambda function that you created earlier, as shown in the following example.

    { "StartAt": "CallTestFunction1", "States": { "CallTestFunction1": { "Type": "Task", "Resource": "arn:aws-cn:lambda:us-east-1:123456789012:function:test-function1", "Catch": [ { "ErrorEquals": [ "States.TaskFailed" ], "Next": "AfterTaskFailed" } ], "Next": "CallTestFunction2" }, "CallTestFunction2": { "Type": "Task", "Resource": "arn:aws-cn:lambda:us-east-1:123456789012:function:test-function2", "Catch": [ { "ErrorEquals": [ "States.TaskFailed" ], "Next": "AfterTaskFailed" } ], "Next": "CallTestFunction3" }, "CallTestFunction3": { "Type": "Task", "Resource": "arn:aws-cn:lambda:us-east-1:123456789012:function:test-function3", "TimeoutSeconds": 5, "Catch": [ { "ErrorEquals": [ "States.Timeout" ], "Next": "AfterTimeout" }, { "ErrorEquals": [ "States.TaskFailed" ], "Next": "AfterTaskFailed" } ], "Next": "Succeed" }, "Succeed": { "Type": "Succeed" }, "AfterTimeout": { "Type": "Fail" }, "AfterTaskFailed": { "Type": "Fail" } } }

    This is a description of your state machine using the Amazon States Language. It defines three Task states named CallTestFunction1, CallTestFunction2 and CallTestFunction3. Each calls one of your three Lambda functions. For more information, see State Machine Structure.

    Choose Next.

  4. Enter a Name, for example, TraceFunctions.

  5. Create or enter an IAM role:

    • To create an IAM role for Step Functions, select Create an IAM role for me, and enter a Name for your role.

    • If you have previously created an IAM role with the correct permissions for your state machine, select Choose an existing IAM role. Select a role from the list, or provide an ARN for that role.

    Note

    If you delete the IAM role that Step Functions creates, Step Functions can't recreate it later. Similarly, if you modify the role (for example, by removing Step Functions from the principals in the IAM policy), Step Functions can't restore its original settings later.

  6. In the Tracing pane, ensure that Enable X-Ray tracing is selected. This will let you view the X-Ray traces of your state machine.

  7. Select Create state machine.

Step 5: Start a New Execution

After you create your state machine, start an execution.

  1. On the TraceFunctions page, choose Start execution.

    The New execution page is displayed.

  2. (Optional) To help identify your execution, you can specify an ID for it in the Enter an execution name box. If you don't enter an ID, Step Functions generates a unique ID automatically.

    Note

    Step Functions allows you to create state machine, execution, and activity names that contain non-ASCII characters. These non-ASCII names don't work with Amazon CloudWatch. To ensure that you can track CloudWatch metrics, choose a name that uses only ASCII characters.

  3. Choose Start Execution.

    A new execution of your state machine starts, and a new page showing your running execution is displayed. Run several (at least three) executions.

  4. After the executions have finished, follow the X-Ray trace map link. You can view the trace while an execution is still running, but you may want to see the execution results before viewing the X-Ray trace map.

    
                            X-Ray enable
  5. View the service map to identify where errors are occurring, connections with high latency, or traces for requests that were unsuccessful. In this example, you can see how much traffic each function is receiving. TestFunction2 was called more often than TestFunction3, and TestFunction1 was called more than twice as often as TestFunction2.

    The service map indicates the health of each node by coloring it based on the ratio of successful calls to errors and faults:

    • Green for successful calls

    • Red for server faults (500 series errors)

    • Yellow for client errors (400 series errors)

    • Purple for throttling errors (429 Too Many Requests)

    
                            X-Ray enable

    You can also choose a service node to view requests for that node, or an edge between two nodes to view requests that traveled that connection.

  6. View the X-Ray trace map to see what has happened for each execution. The Timeline view shows a hierarchy of segments and subsegments. The first entry in the list is the segment, which represents all data recorded by the service for a single request. Below the segment are subsegments. This example shows subsegments recorded by the Lambda functions.

    
                            X-Ray enable

For more information on understanding X-Ray traces and using X-Ray with Step Functions, see the Amazon X-Ray and Step Functions