---
title: 'Handle a failure using Retry'
weight: 103
---

`Task` and `Parallel` states can have a field named `Retry`, whose value must be an array of objects known as retriers. An individual retrier represents a certain number of retries, usually at increasing time intervals.

In the exercise below, you will create an ASL definition that invokes a Lambda function. The Lambda function is designed to fail. You will implement a `Retry` for this function, setting maximum attempts with an exponential backoff rate between retries.

1. Locate the **ErrorHandlingCustomErrorFunction** [Lambda function](https://console.aws.amazon.com/lambda/home). Copy the function ARN and review the code. Notice that the code is configured to throw an error.

   ![Lambda function throws FooError](/static/img/module-8/error-handling-lambda-foo-error.png)

2. Now locate the **ErrorHandlingStateMachineWithRetry-...** [state machine](https://console.aws.amazon.com/states/home). Click on its link and click the **Edit** button on the top right corner of the screen.

3. In the `Resource` field, replace the current value with the ARN of the Lambda function copied in step 1. When the state machine invokes this function, the function will fail. To view the failure Click **Save** and then **Start execution**. Accept the default input and click **Start execution** again.

   ![Replace Lambda function ARN](/static/img/module-8/error-handling-state-machine-retry.png)

4. Now implement a `Retry`. Copy the code shown below and and paste it beginning on line 8 between the `Resource` node and the `End` node.

```bash
      "Retry": [
        {
          "ErrorEquals": [
            "CustomError"
          ],
          "IntervalSeconds": 1,
          "MaxAttempts": 2,
          "BackoffRate": 2
        }
      ],
```

5. Review the Error Handling Parameters. These parameters define the behavior of the `Retry`.

- ErrorEquals (Required)

  > A non-empty array of strings that match error names. When a state reports an error, Step Functions scans through the retriers. When the error name appears in this array, it implements the retry policy described in this retrier.

- IntervalSeconds (Optional)

  > An integer that represents the number of seconds before the first retry attempt (1 by default). IntervalSeconds has a maximum value of 99999999.

- MaxAttempts (Optional)

  > A positive integer that represents the maximum number of retry attempts (3 by default). If the error recurs more times than specified, retries cease and normal error handling resumes. A value of 0 specifies that the error or errors are never retried. MaxAttempts has a maximum value of 99999999.

- BackoffRate (Optional)

  > The multiplier by which the retry interval increases during each attempt (2.0 by default).

Review the documentation for more information about [error handling parameters](https://docs.aws.amazon.com/step-functions/latest/dg/concepts-error-handling.html).

6. Click **Save** and then **Start execution**. Accept the default input and click **Start execution** again.

7. To view your custom error message, select `StartExecution` in the Graph inspector pane and review the **Input and output** tab.
   ![Failure using Retry output](/static/img/module-8/error-handling-custom-error-retry-output.png)

8. Scroll down and review the **Events** table to get more details on the execution. Notice the retries in the event history.
   ![Failure using Retry event history](/static/img/module-8/error-handling-custom-error-retry-event-history.png)

### Having problems?

Your ASL definition should be similar to the snippet below. Remember to replace the Lambda function ARN in the `Resource` node.

```bash
{
  "Comment": "A state machine calling an AWS Lambda function with Retry",
  "StartAt": "StartExecution",
  "States": {
    "StartExecution": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:us-east-1:123456789012:function:FailFunction",
      "Retry": [
        {
          "ErrorEquals": [
            "CustomError"
          ],
          "IntervalSeconds": 1,
          "MaxAttempts": 2,
          "BackoffRate": 2
        }
      ],
      "End": true
    }
  }
}
```

When you are ready, you may move onto the next page.