Invoking SSM Automations from EventBridge - can't pass strings

Question

I am trying to invoke an SSM Automation from EventBridge. However, I can't seem to successfully pass a string to EventBridge.

If I have the following input transformer,

```
{
  "InstanceId": "",
  "Role": ""
}
```
the event ends up in the dead letter queue with the Error Message `Invalid input for target.`

If I try to create the input transformer in the Console, the placeholder text suggests:
```
{
  "InstanceId": [""],
  "Role": [""]
}
```
If I do that, the event gets through EventBridge, but fails at Automation with `Failed to resolve input: InstanceId to type StringList. InstanceId is found to be of type String.` (which isn't surprising).

The SSM Automation is as follows:

```
﻿schemaVersion: '0.3'
parameters:
  InstanceId:
    type: String
  Role:
    type: String
assumeRole: '{{ Role }}'
mainSteps:
  - name: RunCommandOnInstances
    action: aws:runCommand
    isEnd: true
    inputs:
      DocumentName: AWS-RunPowerShellScript
      Parameters:
        commands: 
          - echo "hi"
      InstanceIds: '{{ InstanceId }}'
```

Any thoughts as to what's going wrong here? Unfortunately I can't find examples of anyone doing this.

or-wwn · Accepted Answer

It turns out that:

1. SSM Automation does expect Strings to be passed in inside brackets, as if it were an array
2. The error `Failed to resolve input: InstanceId to type StringList. InstanceId is found to be of type String.` relates to the `InstanceIds` parameter on `RunCommandOnInstances`, not an issue when invoking the Automation with that parameter.

The fix was thus:

```
{
  "InstanceId": [""],
  "Role": [""]
}
```

```
schemaVersion: '0.3'
parameters:
  InstanceId:
    type: StringList
  Role:
    type: String
assumeRole: '{{ Role }}'
mainSteps:
  - name: RunCommandOnInstances
    action: aws:runCommand
    isEnd: true
    inputs:
      DocumentName: AWS-RunPowerShellScript
      Parameters:
        commands: 
          - echo "hi"
      InstanceIds: '{{ InstanceId }}'

Invoking SSM Automations from EventBridge - can't pass strings

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