# Fanout Amazon SNS notifications to Lambda functions for automated processing
<a name="sns-lambda-as-subscriber"></a>

Amazon SNS integrates with AWS Lambda, allowing you to trigger Lambda functions in response to Amazon SNS notifications. When a message is published to an Amazon SNS topic that has a Lambda function subscribed to it, the Lambda function is invoked with the payload of the published message. The Lambda function receives the message payload as an input parameter and can manipulate the information in the message, publish the message to other Amazon SNS topics, or send the message to other AWS services. 

Amazon SNS also supports message delivery status attributes for message notifications sent to Lambda endpoints. For more information, see [Amazon SNS message delivery status](sns-topic-attributes.md). 

**Topics**
+ [Prerequisites](lambda-prereq.md)
+ [Subscribing a function to a topic](lambda-console.md)

# Prerequisites for integrating Amazon SNS with Lambda functions across regions
<a name="lambda-prereq"></a>

To invoke Lambda functions using Amazon SNS notifications, you need the following:
+ A Lambda function
+ An Amazon SNS topic

For information about creating a Lambda function to use with Amazon SNS, see [Using Lambda with Amazon SNS](https://docs.aws.amazon.com/lambda/latest/dg/with-sns-example.html). For information about creating an Amazon SNS topic, see [Create a topic](https://docs.aws.amazon.com/sns/latest/dg/CreateTopic.html).

 When you use Amazon SNS to deliver messages from opt-in regions to regions which are enabled by default, you must alter the policy created in the Lambda function by replacing the principal `sns.amazonaws.com` with `sns.<opt-in-region>.amazonaws.com`. 

 For example, if you want to subscribe a Lambda function in US East (N. Virginia) to an Amazon SNS topic in Asia Pacific (Hong Kong), change the principal in the Lambda function policy to `sns.ap-east-1.amazonaws.com`. Opt-in regions include any regions launched after March 20, 2019, which includes Asia Pacific (Hong Kong), Middle East (Bahrain), EU (Milano), and Africa (Cape Town). Regions launched prior to March 20, 2019 are enabled by default. 

**Note**  
AWS doesn't support cross-region delivery to Lambda from a region that is enabled by default to an opt-in region. Also, cross-region forwarding of Amazon SNS messages from opt-in regions to other opt-in regions is not supported. 

# Subscribing a Lambda function to an Amazon SNS topic
<a name="lambda-console"></a>

This topic explains how to subscribe a Lambda function to an Amazon SNS topic, enabling the function to be triggered by published messages.

1. Sign in to the [Amazon SNS console](https://console.aws.amazon.com/sns/home).

1. On the navigation panel, choose **Topics**.

1. On the **Topics** page, choose a topic.

1. In the **Subscriptions** section, choose **Create subscription**.

1. On the **Create subscription** page, in the **Details** section, do the following:

   1. Verify the chosen **Topic ARN**.

   1. For **Protocol** choose AWS Lambda.

   1. For **Endpoint** enter the ARN of a function.

   1. Choose **Create subscription**.

When a message is published to an Amazon SNS topic that has a Lambda function subscribed to it, the Lambda function is invoked with the payload of the published message. For information about how to use AWS Lambda with Amazon SNS, including a tutorial, see [ Using AWS Lambda with Amazon SNS](https://docs.aws.amazon.com/lambda/latest/dg/with-sns.html).