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# AWS::Greengrass::SubscriptionDefinitionVersion Subscription
<a name="aws-properties-greengrass-subscriptiondefinitionversion-subscription"></a>

<a name="aws-properties-greengrass-subscriptiondefinitionversion-subscription-description"></a>Subscriptions define how MQTT messages can be exchanged between devices, functions, and connectors in the group, and with AWS IoT or the local shadow service. A subscription defines a message source, message target, and a topic (or subject) that's used to route messages from the source to the target. A subscription defines the message flow in one direction, from the source to the target. For two-way communication, you must set up two subscriptions, one for each direction.

<a name="aws-properties-greengrass-subscriptiondefinitionversion-subscription-inheritance"></a> In an CloudFormation template, the `Subscriptions` property of the [https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-greengrass-subscriptiondefinitionversion.html](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-greengrass-subscriptiondefinitionversion.html) resource contains a list of `Subscription` property types.

## Syntax
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To declare this entity in your CloudFormation template, use the following syntax:

### JSON
<a name="aws-properties-greengrass-subscriptiondefinitionversion-subscription-syntax.json"></a>

```
{
  "[Id](#cfn-greengrass-subscriptiondefinitionversion-subscription-id)" : String,
  "[Source](#cfn-greengrass-subscriptiondefinitionversion-subscription-source)" : String,
  "[Subject](#cfn-greengrass-subscriptiondefinitionversion-subscription-subject)" : String,
  "[Target](#cfn-greengrass-subscriptiondefinitionversion-subscription-target)" : String
}
```

### YAML
<a name="aws-properties-greengrass-subscriptiondefinitionversion-subscription-syntax.yaml"></a>

```
  [Id](#cfn-greengrass-subscriptiondefinitionversion-subscription-id): String
  [Source](#cfn-greengrass-subscriptiondefinitionversion-subscription-source): String
  [Subject](#cfn-greengrass-subscriptiondefinitionversion-subscription-subject): String
  [Target](#cfn-greengrass-subscriptiondefinitionversion-subscription-target): String
```

## Properties
<a name="aws-properties-greengrass-subscriptiondefinitionversion-subscription-properties"></a>

`Id`  <a name="cfn-greengrass-subscriptiondefinitionversion-subscription-id"></a>
A descriptive or arbitrary ID for the subscription. This value must be unique within the subscription definition version. Maximum length is 128 characters with pattern `[a-zA-Z0-9:_-]+`.  
*Required*: Yes  
*Type*: String  
*Update requires*: [Replacement](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/using-cfn-updating-stacks-update-behaviors.html#update-replacement)

`Source`  <a name="cfn-greengrass-subscriptiondefinitionversion-subscription-source"></a>
The originator of the message. The value can be a thing ARN, the ARN of a Lambda function alias (recommended) or version, a connector ARN, `cloud` (which represents the AWS IoT cloud), or `GGShadowService`.  
*Required*: Yes  
*Type*: String  
*Update requires*: [Replacement](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/using-cfn-updating-stacks-update-behaviors.html#update-replacement)

`Subject`  <a name="cfn-greengrass-subscriptiondefinitionversion-subscription-subject"></a>
The MQTT topic used to route the message.  
*Required*: Yes  
*Type*: String  
*Update requires*: [Replacement](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/using-cfn-updating-stacks-update-behaviors.html#update-replacement)

`Target`  <a name="cfn-greengrass-subscriptiondefinitionversion-subscription-target"></a>
The destination of the message. The value can be a thing ARN, the ARN of a Lambda function alias (recommended) or version, a connector ARN, `cloud` (which represents the AWS IoT cloud), or `GGShadowService`.  
*Required*: Yes  
*Type*: String  
*Update requires*: [Replacement](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/using-cfn-updating-stacks-update-behaviors.html#update-replacement)

## See also
<a name="aws-properties-greengrass-subscriptiondefinitionversion-subscription--seealso"></a>
+ [Subscription](https://docs.aws.amazon.com/greengrass/v1/apireference/definitions-subscription.html) in the * AWS IoT Greengrass Version 1 API Reference *
+  [AWS IoT Greengrass Version 1 Developer Guide](https://docs.aws.amazon.com/greengrass/v1/developerguide/)