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# `aws:loop` – Iterate over steps in an automation
<a name="automation-action-loop"></a>

This action iterates over a subset of steps in an automation runbook. You can choose a `do while` or `for each` style loop. To construct a `do while` loop, use the `LoopCondition` input parameter. To construct a `for each` loop, use the `Iterators` and `IteratorDataType` input parameters. When using an `aws:loop` action, only specify either the `Iterators` or `LoopCondition` input parameter. The maximum number of iterations is 100.

The `onCancel` property can only be used for steps defined within a loop. The `onCancel` property isn't supported for the `aws:loop` action. The `onFailure` property can be used for an `aws:loop` action, however it will only be used if an unexpected error occurs causing the step to fail. If you define `onFailure` properties for the steps within a loop, the `aws:loop` action inherits those properties and reacts accordingly when a failure occurs.

**Examples**  
The following are examples of how to construct the different types of loop actions.

------
#### [ do while ]

```
name: RepeatMyLambdaFunctionUntilOutputIsReturned
action: aws:loop
inputs:
    Steps:
    - name: invokeMyLambda
        action: aws:invokeLambdaFunction
        inputs:
        FunctionName: LambdaFunctionName
        outputs:
        - Name: ShouldRetry
            Selector: $.Retry
            Type: Boolean
    LoopCondition:
        Variable: "{{ invokeMyLambda.ShouldRetry }}"
        BooleanEquals: true
    MaxIterations: 3
```

------
#### [ for each ]

```
name: stopAllInstancesWithWaitTime
action: aws:loop
inputs:
    Iterators: "{{ DescribeInstancesStep.InstanceIds }}"
    IteratorDataType: "String"
    Steps:
    - name: stopOneInstance
        action: aws:changeInstanceState
        inputs:
        InstanceIds:
            - "{{stopAllInstancesWithWaitTime.CurrentIteratorValue}}"
        CheckStateOnly: false
        DesiredState: stopped
    - name: wait10Seconds
        action: aws:sleep
        inputs:
        Duration: PT10S
```

------

**Input**  
The input is as follows.

Iterators  
The list of items for the steps to iterate over. The maximum number of iterators is 100.  
Type: StringList  
Required: No

IteratorDataType  
An optional parameter to specify the data type of the `Iterators`. A value for this parameter can be provided along with the `Iterators` input parameter. If you don’t specify a value for this parameter and `Iterators`, then you must specify a value for the `LoopCondition` parameter.  
Type: String  
Valid values: Boolean \$1 Integer \$1 String \$1 StringMap  
Default: String  
Required: No

LoopCondition  
Consists of a `Variable` and an operator condition to evaluate. If you don’t specify a value for this parameter, then you must specify values for the `Iterators` and `IteratorDataType` parameters. You can use complex operator evaluations by using a combination of `And`, `Not`, and `Or` operators. The condition is evaluated after the steps in the loop complete. If the condition is `true` and the `MaxIterations` value has not been reached, the steps in the loop run again. The operator conditions are as follows:  

**String operations**
+ StringEquals
+ EqualsIgnoreCase
+ StartsWith
+ EndsWith
+ Contains

**Numeric operations**
+ NumericEquals
+ NumericGreater
+ NumericLesser
+ NumericGreaterOrEquals
+ NumericLesser
+ NumericLesserOrEquals

**Boolean operation**
+ BooleanEquals
Type: StringMap  
Required: No

MaxIterations  
The maximum number of times the steps in the loop run. Once the value specified for this input is reached, the loop stops running even if the `LoopCondition` is still `true` or if there are objects remaining in the `Iterators` parameter.  
Type: Integer  
Valid values: 1 - 100  
Required: No

Steps  
The list of steps to run in the loop. These function like a nested runbook. Within these steps you can access the current iterator value for a `for each` loop using the syntax `{{loopStepName.CurrentIteratorValue}}`. You can also access an integer value of the current iteration for both loop types using the syntax `{{loopStepName.CurrentIteration}}`.  
Type: List of steps  
Required: YesOutput

CurrentIteration  
The current loop iteration as an integer. Iteration values start at 1.  
Type: Integer

CurrentIteratorValue  
The value of the current iterator as a string. This output is only present in `for each` loops.  
Type: String