# Legacy subscription router
<a name="legacy-subscription-router-component"></a>

The legacy subscription router (`aws.greengrass.LegacySubscriptionRouter`) manages subscriptions on the Greengrass core device. Subscriptions are a feature of AWS IoT Greengrass V1 that define the topics that Lambda functions can use for MQTT messaging on a core device. For more information, see [Managed subscriptions in the MQTT messaging workflow](https://docs.aws.amazon.com/greengrass/v1/developerguide/gg-sec.html#gg-msg-workflow) in the *AWS IoT Greengrass V1 Developer Guide*.

You can use this component to enable subscriptions for connector components and Lambda function components that use the AWS IoT Greengrass Core SDK.

**Note**  <a name="legacy-subscription-router-requirement-note"></a>
The legacy subscription router component is required only if your Lambda function uses the `publish()` function in the AWS IoT Greengrass Core SDK. If you update your Lambda function code to use the interprocess communication (IPC) interface in the AWS IoT Device SDK V2, you don't need to deploy the legacy subscription router component. For more information, see the following [interprocess communication](interprocess-communication.md) services:  
[Publish/subscribe local messages](ipc-publish-subscribe.md)
[Publish/subscribe AWS IoT Core MQTT messages](ipc-iot-core-mqtt.md)

**Topics**
+ [Versions](#legacy-subscription-router-component-versions)
+ [Type](#legacy-subscription-router-component-type)
+ [Operating system](#legacy-subscription-router-component-os-support)
+ [Requirements](#legacy-subscription-router-component-requirements)
+ [Dependencies](#legacy-subscription-router-component-dependencies)
+ [Configuration](#legacy-subscription-router-component-configuration)
+ [Local log file](#legacy-subscription-router-component-log-file)
+ [Changelog](#legacy-subscription-router-component-changelog)

## Versions
<a name="legacy-subscription-router-component-versions"></a>

This component has the following versions:
+ 2.1.x
+ 2.0.x

## Type
<a name="legacy-subscription-router-component-type"></a>

<a name="public-component-type-generic"></a>This <a name="public-component-type-generic-phrase"></a>component is a generic component (`aws.greengrass.generic`). The [Greengrass nucleus](greengrass-nucleus-component.md) runs the component's lifecycle scripts.

<a name="public-component-type-more-information"></a>For more information, see [Component types](develop-greengrass-components.md#component-types).

## Operating system
<a name="legacy-subscription-router-component-os-support"></a>

This component can be installed on Linux core devices only.

## Requirements
<a name="legacy-subscription-router-component-requirements"></a>

This component has the following requirements:
+ The legacy subscription router is supported to run in a VPC.

## Dependencies
<a name="legacy-subscription-router-component-dependencies"></a>

When you deploy a component, AWS IoT Greengrass also deploys compatible versions of its dependencies. This means that you must meet the requirements for the component and all of its dependencies to successfully deploy the component. This section lists the dependencies for the [released versions](#legacy-subscription-router-component-changelog) of this component and the semantic version constraints that define the component versions for each dependency. You can also view the dependencies for each version of the component in the [AWS IoT Greengrass console](https://console.aws.amazon.com//greengrass). On the component details page, look for the **Dependencies** list.

------
#### [ 2.1.15 ]

The following table lists the dependencies for version 2.1.15 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.17.0 | Soft | 

------
#### [ 2.1.14 ]

The following table lists the dependencies for version 2.1.14 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.16.0 | Soft | 

------
#### [ 2.1.13 ]

The following table lists the dependencies for version 2.1.13 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.15.0 | Soft | 

------
#### [ 2.1.12 ]

The following table lists the dependencies for version 2.1.12 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.14.0 | Soft | 

------
#### [ 2.1.11 ]

The following table lists the dependencies for version 2.1.11 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.13.0 | Soft | 

------
#### [ 2.1.10 ]

The following table lists the dependencies for version 2.1.10 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.12.0 | Soft | 

------
#### [ 2.1.9 ]

The following table lists the dependencies for version 2.1.9 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.11.0 | Soft | 

------
#### [ 2.1.8 ]

The following table lists the dependencies for version 2.1.8 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.10.0 | Soft | 

------
#### [ 2.1.7 ]

The following table lists the dependencies for version 2.1.7 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.9.0 | Soft | 

------
#### [ 2.1.6 ]

The following table lists the dependencies for version 2.1.6 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.8.0 | Soft | 

------
#### [ 2.1.5 ]

The following table lists the dependencies for version 2.1.5 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.7.0 | Soft | 

------
#### [ 2.1.4 ]

The following table lists the dependencies for version 2.1.4 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.6.0 | Soft | 

------
#### [ 2.1.3 ]

The following table lists the dependencies for version 2.1.3 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.5.0 | Soft | 

------
#### [ 2.1.2 ]

The following table lists the dependencies for version 2.1.2 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.4.0 | Soft | 

------
#### [ 2.1.1 ]

The following table lists the dependencies for version 2.1.1 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.3.0 | Soft | 

------
#### [ 2.1.0 ]

The following table lists the dependencies for version 2.1.0 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.0 <2.2.0 | Soft | 

------
#### [ 2.0.3 ]

The following table lists the dependencies for version 2.0.3 of this component.


| Dependency | Compatible versions | Dependency type | 
| --- | --- | --- | 
| [Greengrass nucleus](greengrass-nucleus-component.md) | >=2.0.3 <2.1.0 | Soft | 

------

For more information about component dependencies, see the [component recipe reference](component-recipe-reference.md#recipe-reference-component-dependencies).

## Configuration
<a name="legacy-subscription-router-component-configuration"></a>

This component provides the following configuration parameters that you can customize when you deploy the component.

------
#### [ v2.1.x ]

`subscriptions`  
<a name="legacy-subscription-router-component-configuration-subscriptions-intro"></a>(Optional) The subscriptions to enable on the core device. This is an object, where each key is a unique ID, and each value is an object that defines the subscription for that connector. You must configure a subscription when you deploy a V1 connector component or a Lambda function that uses the AWS IoT Greengrass Core SDK.  
Each subscription object contains the following information:    
`id`  <a name="legacy-subscription-router-component-configuration-subscription-id"></a>
The unique ID of this subscription. This ID must match the key for this subscription object.  
`source`  
The Lambda function that uses the AWS IoT Greengrass Core SDK to publish MQTT messages on the topics that you specify in `subject`. Specify one of the following:  
+ <a name="legacy-subscription-router-component-configuration-subscription-source-target-component-name"></a>The name of a Lambda function component on the core device. Specify the component name with the `component:` prefix, such as **component:com.example.HelloWorldLambda**.
+ <a name="legacy-subscription-router-component-configuration-subscription-source-target-function-arn"></a>The Amazon Resource Name (ARN) of a Lambda function on the core device.
**Important**  <a name="legacy-subscription-router-function-version-requirement"></a>
If the version of the Lambda function changes, you must configure the subscription with the new version of the function. Otherwise, this component won't route the messages until the version matches the subscription.  
You must specify an Amazon Resource Name (ARN) that includes the version of the function to import. You can't use version aliases like `$LATEST`.
To deploy a subscription for a V1 connector component, specify the name of the component or the ARN of the connector component's Lambda function.  
`subject`  <a name="legacy-subscription-router-component-configuration-subscription-subject"></a>
The MQTT topic or topic filter on which the source and target can publish and receive messages. This value supports the `+` and `#` topic wildcards.  
`target`  
<a name="legacy-subscription-router-component-configuration-subscription-target-intro"></a>The target that receives the MQTT messages on the topics that you specify in `subject`. The subscription specifies that the `source` function publishes MQTT messages to AWS IoT Core or to a Lambda function on the core device. Specify one of the following:  
+ <a name="legacy-subscription-router-component-configuration-subscription-target-cloud"></a>`cloud`. The `source` function publishes MQTT messages to AWS IoT Core.
+ <a name="legacy-subscription-router-component-configuration-subscription-source-target-component-name"></a>The name of a Lambda function component on the core device. Specify the component name with the `component:` prefix, such as **component:com.example.HelloWorldLambda**.
+ <a name="legacy-subscription-router-component-configuration-subscription-source-target-function-arn"></a>The Amazon Resource Name (ARN) of a Lambda function on the core device.
**Important**  <a name="legacy-subscription-router-function-version-requirement"></a>
If the version of the Lambda function changes, you must configure the subscription with the new version of the function. Otherwise, this component won't route the messages until the version matches the subscription.  
You must specify an Amazon Resource Name (ARN) that includes the version of the function to import. You can't use version aliases like `$LATEST`.
Default: No subscriptions

**Example configuration update (defining a subscription to AWS IoT Core)**  
The following example specifies that the `com.example.HelloWorldLambda` Lambda function component publishes MQTT message to AWS IoT Core on the `hello/world` topic.  

```
{
  "subscriptions": {
    "Greengrass_HelloWorld_to_cloud": {
      "id": "Greengrass_HelloWorld_to_cloud",
      "source": "component:com.example.HelloWorldLambda",
      "subject": "hello/world",
      "target": "cloud"
    }
  }
}
```

**Example configuration update (defining a subscription to another Lambda function)**  
The following example specifies that the `com.example.HelloWorldLambda` Lambda function component publishes MQTT messages to the `com.example.MessageRelay` Lambda function component on the `hello/world` topic.  

```
{
  "subscriptions": {
    "Greengrass_HelloWorld_to_MessageRelay": {
      "id": "Greengrass_HelloWorld_to_MessageRelay",
      "source": "component:com.example.HelloWorldLambda",
      "subject": "hello/world",
      "target": "component:com.example.MessageRelay"
    }
  }
}
```

------
#### [ v2.0.x ]

`subscriptions`  
<a name="legacy-subscription-router-component-configuration-subscriptions-intro"></a>(Optional) The subscriptions to enable on the core device. This is an object, where each key is a unique ID, and each value is an object that defines the subscription for that connector. You must configure a subscription when you deploy a V1 connector component or a Lambda function that uses the AWS IoT Greengrass Core SDK.  
Each subscription object contains the following information:    
`id`  <a name="legacy-subscription-router-component-configuration-subscription-id"></a>
The unique ID of this subscription. This ID must match the key for this subscription object.  
`source`  
The Lambda function that uses the AWS IoT Greengrass Core SDK to publish MQTT messages on the topics that you specify in `subject`. Specify the following:  
+ <a name="legacy-subscription-router-component-configuration-subscription-source-target-function-arn"></a>The Amazon Resource Name (ARN) of a Lambda function on the core device.
**Important**  <a name="legacy-subscription-router-function-version-requirement"></a>
If the version of the Lambda function changes, you must configure the subscription with the new version of the function. Otherwise, this component won't route the messages until the version matches the subscription.  
You must specify an Amazon Resource Name (ARN) that includes the version of the function to import. You can't use version aliases like `$LATEST`.
To deploy a subscription for a V1 connector component, specify the ARN of the connector component's Lambda function.  
`subject`  <a name="legacy-subscription-router-component-configuration-subscription-subject"></a>
The MQTT topic or topic filter on which the source and target can publish and receive messages. This value supports the `+` and `#` topic wildcards.  
`target`  
<a name="legacy-subscription-router-component-configuration-subscription-target-intro"></a>The target that receives the MQTT messages on the topics that you specify in `subject`. The subscription specifies that the `source` function publishes MQTT messages to AWS IoT Core or to a Lambda function on the core device. Specify one of the following:  
+ <a name="legacy-subscription-router-component-configuration-subscription-target-cloud"></a>`cloud`. The `source` function publishes MQTT messages to AWS IoT Core.
+ <a name="legacy-subscription-router-component-configuration-subscription-source-target-function-arn"></a>The Amazon Resource Name (ARN) of a Lambda function on the core device.
**Important**  <a name="legacy-subscription-router-function-version-requirement"></a>
If the version of the Lambda function changes, you must configure the subscription with the new version of the function. Otherwise, this component won't route the messages until the version matches the subscription.  
You must specify an Amazon Resource Name (ARN) that includes the version of the function to import. You can't use version aliases like `$LATEST`.
Default: No subscriptions

**Example configuration update (defining a subscription to AWS IoT Core)**  
The following example specifies that the `Greengrass_HelloWorld` function publishes MQTT message to AWS IoT Core on the `hello/world` topic.  

```
"subscriptions": {
  "Greengrass_HelloWorld_to_cloud": {
    "id": "Greengrass_HelloWorld_to_cloud",
    "source": "arn:aws:lambda:us-west-2:123456789012:function:Greengrass_HelloWorld:5",
    "subject": "hello/world",
    "target": "cloud"
  }
}
```

**Example configuration update (defining a subscription to another Lambda function)**  
The following example specifies that the `Greengrass_HelloWorld` function publishes MQTT messages to the `Greengrass_MessageRelay` on the `hello/world` topic.  

```
"subscriptions": {
  "Greengrass_HelloWorld_to_MessageRelay": {
    "id": "Greengrass_HelloWorld_to_MessageRelay",
    "source": "arn:aws:lambda:us-west-2:123456789012:function:Greengrass_HelloWorld:5",
    "subject": "hello/world",
    "target": "arn:aws:lambda:us-west-2:123456789012:function:Greengrass_MessageRelay:5"
  }
}
```

------

## Local log file
<a name="legacy-subscription-router-component-log-file"></a>

This component doesn't output logs.

## Changelog
<a name="legacy-subscription-router-component-changelog"></a>

The following table describes the changes in each version of the component.


|  Version  |  Changes  | 
| --- | --- | 
|  2.1.16  |  Updates the component version for the Greengrass nucleus version 2.17.0 release.  | 
|  2.1.15  |  Version updated for Greengrass nucleus version 2.16.0 release.  | 
|  2.1.14  | Version updated for Greengrass nucleus version 2.15.0 release. | 
|  2.1.13  | Version updated for Greengrass nucleus version 2.14.0 release. | 
|  2.1.12  | Version updated for Greengrass nucleus version 2.13.0 release. | 
|  2.1.11  | Version updated for Greengrass nucleus version 2.12.0 release. | 
|  2.1.10  | Version updated for Greengrass nucleus version 2.11.0 release. | 
|  2.1.9  | Version updated for Greengrass nucleus version 2.10.0 release. | 
|  2.1.8  | Version updated for Greengrass nucleus version 2.9.0 release. | 
|  2.1.7  | Version updated for Greengrass nucleus version 2.8.0 release. | 
|  2.1.6  |  Version updated for Greengrass nucleus version 2.7.0 release.  | 
|  2.1.5  |  Version updated for Greengrass nucleus version 2.6.0 release.  | 
|  2.1.4  |  Version updated for Greengrass nucleus version 2.5.0 release.  | 
|  2.1.3  |  Version updated for Greengrass nucleus version 2.4.0 release.  | 
|  2.1.2  |  Version updated for Greengrass nucleus version 2.3.0 release.  | 
|  2.1.1  |  Version updated for Greengrass nucleus version 2.2.0 release.  | 
|  2.1.0  |  <a name="changelog-legacy-subscription-router-2.1.0"></a>[\[See the AWS documentation website for more details\]](http://docs.aws.amazon.com/greengrass/v2/developerguide/legacy-subscription-router-component.html)  | 
|  2.0.3  |  Initial version.  |