Tutorial: Using AWS Lambda with Amazon Simple Notification Service

Prerequisites Create an Amazon SNS topic (account A)Create a function execution role (account B)Create a Lambda function (account B)Add permissions to function (account B)Grant cross-account permission for Amazon SNS subscription (account A)Create a subscription (account B)Publish messages to topic (account A and account B)Clean up your resources

In this tutorial, you use a Lambda function in one AWS account to subscribe to an Amazon Simple Notification Service (Amazon SNS) topic in a separate AWS account. When you publish messages to your Amazon SNS topic, your Lambda function reads the contents of the message and outputs it to Amazon CloudWatch Logs. To complete this tutorial, you use the AWS Command Line Interface (AWS CLI).

An Amazon SNS topic connected to a Lambda function connected to a CloudWatch Logs log group

To complete this tutorial, you perform the following steps:

In account A, create an Amazon SNS topic.
In account B, create a Lambda function that will read messages from the topic.
In account B, create a subscription to the topic.
Publish messages to the Amazon SNS topic in account A and confirm that the Lambda function in account B outputs them to CloudWatch Logs.

By completing these steps, you will learn how to configure an Amazon SNS topic to invoke a Lambda function. You will also learn how to create an AWS Identity and Access Management (IAM) policy that gives permission for a resource in another AWS account to invoke Lambda.

In the tutorial, you use two separate AWS accounts. The AWS CLI commands illustrate this by using two named profiles called accountA and accountB, each configured for use with a different AWS account. To learn how to configure the AWS CLI to use different profiles, see Configuration and credential file settings in the AWS Command Line Interface User Guide for Version 2. Be sure to configure the same default AWS Region for both profiles.

If the AWS CLI profiles you create for the two AWS accounts use different names, or if you use the default profile and one named profile, modify the AWS CLI commands in the following steps as needed.

If you have not yet installed the AWS Command Line Interface, follow the steps at Installing or updating the latest version of the AWS CLI to install it.

The tutorial requires a command line terminal or shell to run commands. In Linux and macOS, use your preferred shell and package manager.

Note

In Windows, some Bash CLI commands that you commonly use with Lambda (such as zip) are not supported by the operating system's built-in terminals. To get a Windows-integrated version of Ubuntu and Bash, install the Windows Subsystem for Linux.

To create the topic

In account A, create an Amazon SNS standard topic using the following AWS CLI command.
```
aws sns create-topic --name sns-topic-for-lambda --profile accountA
```
You should see output similar to the following.
```
{
    "TopicArn": "arn:aws:sns:us-west-2:123456789012:sns-topic-for-lambda"
}
```
Make a note of the Amazon Resource Name (ARN) of your topic. You’ll need it later in the tutorial when you add permissions to your Lambda function to subscribe to the topic.

An execution role is an IAM role that grants a Lambda function permission to access AWS services and resources. Before you create your function in account B, you create a role that gives the function basic permissions to write logs to CloudWatch Logs. We’ll add the permissions to read from your Amazon SNS topic in a later step.

To create an execution role

In account B open the roles page in the IAM console.
Choose Create role.
For Trusted entity type, choose AWS service.
For Use case, choose Lambda.
Choose Next.
Add a basic permissions policy to the role by doing the following:
1. In the Permissions policies search box, enter AWSLambdaBasicExecutionRole.
2. Choose Next.
Finalize the role creation by doing the following:
1. Under Role details, enter lambda-sns-role for Role name.
2. Choose Create role.

Create a Lambda function that processes your Amazon SNS messages. The function code logs the message contents of each record to Amazon CloudWatch Logs.

This tutorial uses the Node.js 18.x runtime, but we've also provided example code in other runtime languages. You can select the tab in the following box to see code for the runtime you're interested in. The JavaScript code you'll use in this step is in the first example shown in the JavaScript tab.

.NET

AWS SDK for .NET

Note

There's more on GitHub. Find the complete example and learn how to set up and run in the Serverless examples repository.

Consuming an SNS event with Lambda using .NET.


// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
using Amazon.Lambda.Core;
using Amazon.Lambda.SNSEvents;


// Assembly attribute to enable the Lambda function's JSON input to be converted into a .NET class.
[assembly: LambdaSerializer(typeof(Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer))]

namespace SnsIntegration;

public class Function
{
    public async Task FunctionHandler(SNSEvent evnt, ILambdaContext context)
    {
        foreach (var record in evnt.Records)
        {
            await ProcessRecordAsync(record, context);
        }
        context.Logger.LogInformation("done");
    }

    private async Task ProcessRecordAsync(SNSEvent.SNSRecord record, ILambdaContext context)
    {
        try
        {
            context.Logger.LogInformation($"Processed record {record.Sns.Message}");

            // TODO: Do interesting work based on the new message
            await Task.CompletedTask;
        }
        catch (Exception e)
        {
            //You can use Dead Letter Queue to handle failures. By configuring a Lambda DLQ.
            context.Logger.LogError($"An error occurred");
            throw;
        }
    }
}

Go

SDK for Go V2

Note

There's more on GitHub. Find the complete example and learn how to set up and run in the Serverless examples repository.

Consuming an SNS event with Lambda using Go.


// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
package main

import (
	"context"
	"fmt"

	"github.com/aws/aws-lambda-go/events"
	"github.com/aws/aws-lambda-go/lambda"
)

func handler(ctx context.Context, snsEvent events.SNSEvent) {
	for _, record := range snsEvent.Records {
		processMessage(record)
	}
	fmt.Println("done")
}

func processMessage(record events.SNSEventRecord) {
	message := record.SNS.Message
	fmt.Printf("Processed message: %s\n", message)
	// TODO: Process your record here
}

func main() {
	lambda.Start(handler)
}

Java

SDK for Java 2.x

Note

There's more on GitHub. Find the complete example and learn how to set up and run in the Serverless examples repository.

Consuming an SNS event with Lambda using Java.


// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
package example;

import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.LambdaLogger;
import com.amazonaws.services.lambda.runtime.RequestHandler;
import com.amazonaws.services.lambda.runtime.events.SNSEvent;
import com.amazonaws.services.lambda.runtime.events.SNSEvent.SNSRecord;


import java.util.Iterator;
import java.util.List;

public class SNSEventHandler implements RequestHandler<SNSEvent, Boolean> {
    LambdaLogger logger;

    @Override
    public Boolean handleRequest(SNSEvent event, Context context) {
        logger = context.getLogger();
        List<SNSRecord> records = event.getRecords();
        if (!records.isEmpty()) {
            Iterator<SNSRecord> recordsIter = records.iterator();
            while (recordsIter.hasNext()) {
                processRecord(recordsIter.next());
            }
        }
        return Boolean.TRUE;
    }

    public void processRecord(SNSRecord record) {
        try {
            String message = record.getSNS().getMessage();
            logger.log("message: " + message);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

}

JavaScript

SDK for JavaScript (v3)

Note

There's more on GitHub. Find the complete example and learn how to set up and run in the Serverless examples repository.

Consuming an SNS event with Lambda using JavaScript.


// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
exports.handler = async (event, context) => {
  for (const record of event.Records) {
    await processMessageAsync(record);
  }
  console.info("done");
};

async function processMessageAsync(record) {
  try {
    const message = JSON.stringify(record.Sns.Message);
    console.log(`Processed message ${message}`);
    await Promise.resolve(1); //Placeholder for actual async work
  } catch (err) {
    console.error("An error occurred");
    throw err;
  }
}

Consuming an SNS event with Lambda using TypeScript.


// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
import { SNSEvent, Context, SNSHandler, SNSEventRecord } from "aws-lambda";

export const functionHandler: SNSHandler = async (
  event: SNSEvent,
  context: Context
): Promise<void> => {
  for (const record of event.Records) {
    await processMessageAsync(record);
  }
  console.info("done");
};

async function processMessageAsync(record: SNSEventRecord): Promise<any> {
  try {
    const message: string = JSON.stringify(record.Sns.Message);
    console.log(`Processed message ${message}`);
    await Promise.resolve(1); //Placeholder for actual async work
  } catch (err) {
    console.error("An error occurred");
    throw err;
  }
}

PHP

SDK for PHP

Note

There's more on GitHub. Find the complete example and learn how to set up and run in the Serverless examples repository.

Consuming an SNS event with Lambda using PHP.


// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
<?php

/* 
Since native PHP support for AWS Lambda is not available, we are utilizing Bref's PHP functions runtime for AWS Lambda.
For more information on Bref's PHP runtime for Lambda, refer to: https://bref.sh/docs/runtimes/function

Another approach would be to create a custom runtime. 
A practical example can be found here: https://aws.amazon.com/blogs/apn/aws-lambda-custom-runtime-for-php-a-practical-example/
*/

// Additional composer packages may be required when using Bref or any other PHP functions runtime.
// require __DIR__ . '/vendor/autoload.php';

use Bref\Context\Context;
use Bref\Event\Sns\SnsEvent;
use Bref\Event\Sns\SnsHandler;

class Handler extends SnsHandler
{
    public function handleSns(SnsEvent $event, Context $context): void
    {
        foreach ($event->getRecords() as $record) {
            $message = $record->getMessage();

            // TODO: Implement your custom processing logic here
            // Any exception thrown will be logged and the invocation will be marked as failed

            echo "Processed Message: $message" . PHP_EOL;
        }
    }
}

return new Handler();

Python

SDK for Python (Boto3)

Note

There's more on GitHub. Find the complete example and learn how to set up and run in the Serverless examples repository.

Consuming an SNS event with Lambda using Python.


# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
# SPDX-License-Identifier: Apache-2.0
def lambda_handler(event, context):
    for record in event['Records']:
        process_message(record)
    print("done")

def process_message(record):
    try:
        message = record['Sns']['Message']
        print(f"Processed message {message}")
        # TODO; Process your record here
        
    except Exception as e:
        print("An error occurred")
        raise e

Ruby

SDK for Ruby

Note

There's more on GitHub. Find the complete example and learn how to set up and run in the Serverless examples repository.

Consuming an SNS event with Lambda using Ruby.


# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
# SPDX-License-Identifier: Apache-2.0
def lambda_handler(event:, context:)
  event['Records'].map { |record| process_message(record) }
end

def process_message(record)
  message = record['Sns']['Message']
  puts("Processing message: #{message}")
rescue StandardError => e
  puts("Error processing message: #{e}")
  raise
end

Rust

SDK for Rust

Note

There's more on GitHub. Find the complete example and learn how to set up and run in the Serverless examples repository.

Consuming an SNS event with Lambda using Rust.


// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
use aws_lambda_events::event::sns::SnsEvent;
use aws_lambda_events::sns::SnsRecord;
use lambda_runtime::{run, service_fn, Error, LambdaEvent};
use tracing::info;

// Built with the following dependencies:
//  aws_lambda_events = { version = "0.10.0", default-features = false, features = ["sns"] }
//  lambda_runtime = "0.8.1"
//  tokio = { version = "1", features = ["macros"] }
//  tracing = { version = "0.1", features = ["log"] }
//  tracing-subscriber = { version = "0.3", default-features = false, features = ["fmt"] }

async fn function_handler(event: LambdaEvent<SnsEvent>) -> Result<(), Error> {
    for event in event.payload.records {
        process_record(&event)?;
    }
    
    Ok(())
}

fn process_record(record: &SnsRecord) -> Result<(), Error> {
    info!("Processing SNS Message: {}", record.sns.message);

    // Implement your record handling code here.

    Ok(())
}

#[tokio::main]
async fn main() -> Result<(), Error> {
    tracing_subscriber::fmt()
        .with_max_level(tracing::Level::INFO)
        .with_target(false)
        .without_time()
        .init();

    run(service_fn(function_handler)).await
}

To create the function

Create a directory for the project, and then switch to that directory.
```
mkdir sns-tutorial
cd sns-tutorial
```
Copy the sample JavaScript code into a new file named index.js.
Create a deployment package using the following zip command.
```
zip function.zip index.js
```

Run the following AWS CLI command to create your Lambda function in account B.


aws lambda create-function --function-name Function-With-SNS \
    --zip-file fileb://function.zip --handler index.handler --runtime nodejs18.x \
    --role arn:aws:iam::<AccountB_ID>:role/lambda-sns-role  \
    --timeout 60 --profile accountB

You should see output similar to the following.


{
    "FunctionName": "Function-With-SNS",
    "FunctionArn": "arn:aws:lambda:us-west-2:123456789012:function:Function-With-SNS",
    "Runtime": "nodejs18.x",
    "Role": "arn:aws:iam::123456789012:role/lambda_basic_role",
    "Handler": "index.handler",
    ...
    "RuntimeVersionConfig": {
        "RuntimeVersionArn": "arn:aws:lambda:us-west-2::runtime:7d5f06b69c951da8a48b926ce280a9daf2e8bb1a74fc4a2672580c787d608206"
    }
}

Record the Amazon Resource Name (ARN) of your function. You’ll need it later in the tutorial when you add permissions to allow Amazon SNS to invoke your function.

For Amazon SNS to invoke your function, you need to grant it permission in a statement on a resource-based policy. You add this statement using the AWS CLI add-permission command.

To grant Amazon SNS permission to invoke your function

In account B, run the following AWS CLI command using the ARN for your Amazon SNS topic you recorded earlier.


aws lambda add-permission --function-name Function-With-SNS \
    --source-arn arn:aws:sns:us-east-1:<AccountA_ID>:sns-topic-for-lambda \
    --statement-id function-with-sns --action "lambda:InvokeFunction" \
    --principal sns.amazonaws.com --profile accountB

You should see output similar to the following.


{
    "Statement": "{\"Condition\":{\"ArnLike\":{\"AWS:SourceArn\":
      \"arn:aws:sns:us-east-1:<AccountA_ID>:sns-topic-for-lambda\"}},
      \"Action\":[\"lambda:InvokeFunction\"],
      \"Resource\":\"arn:aws:lambda:us-east-1:<AccountB_ID>:function:Function-With-SNS\",
      \"Effect\":\"Allow\",\"Principal\":{\"Service\":\"sns.amazonaws.com\"},
      \"Sid\":\"function-with-sns\"}"
}

Note

If the account with the Amazon SNS topic is hosted in an opt-in AWS Region, you need to specify the region in the principal. For example, if you're working with an Amazon SNS topic in the Asia Pacific (Hong Kong) region, you need to specify sns.ap-east-1.amazonaws.com instead of sns.amazonaws.com for the principal.

Next step: Grant cross-account permission

For your Lambda function in account B to subscribe to the Amazon SNS topic you created in account A, you need to grant permission for account B to subscribe to your topic. You grant this permission using the AWS CLI add-permission command.

To grant permission for account B to subscribe to the topic

In account A, run the following AWS CLI command. Use the ARN for the Amazon SNS topic you recorded earlier.


aws sns add-permission --label lambda-access --aws-account-id <AccountB_ID> \
    --topic-arn arn:aws:sns:us-east-1:<AccountA_ID>:sns-topic-for-lambda \  
    --action-name Subscribe ListSubscriptionsByTopic --profile accountA

In account B, you now subscribe your Lambda function to the Amazon SNS topic you created at the beginning of the tutorial in account A. When a message is sent to this topic (sns-topic-for-lambda), Amazon SNS invokes your Lambda function Function-With-SNS in account B.

To create a subscription

In account B, run the following AWS CLI command. Use your default region you created your topic in and the ARNs for your topic and Lambda function.


aws sns subscribe --protocol lambda \
    --region us-east-1 \
    --topic-arn arn:aws:sns:us-east-1:<AccountA_ID>:sns-topic-for-lambda \
    --notification-endpoint arn:aws:lambda:us-east-1:<AccountB_ID>:function:Function-With-SNS \
    --profile accountB

You should see output similar to the following.


{
    "SubscriptionArn": "arn:aws:sns:us-east-1:<AccountA_ID>:sns-topic-for-lambda:5d906xxxx-7c8x-45dx-a9dx-0484e31c98xx"
}

Now that your Lambda function in account B is subscribed to your Amazon SNS topic in account A, it’s time to test your setup by publishing messages to your topic. To confirm that Amazon SNS has invoked your Lambda function, you use CloudWatch Logs to view your function’s output.

To publish a message to your topic and view your function's output

Enter Hello World into a text file and save it as message.txt.
From the same directory you saved your text file in, run the following AWS CLI command in account A. Use the ARN for your own topic.
```
aws sns publish --message file://message.txt --subject Test \
    --topic-arn arn:aws:sns:us-east-1:<AccountA_ID>:sns-topic-for-lambda \
    --profile accountA
```
This will return a message ID with a unique identifier, indicating that Amazon SNS has accepted the message. Amazon SNS then attempts to deliver the message to the topic’s subscribers. To confirm that Amazon SNS has invoked your Lambda function, use CloudWatch Logs to view your function’s output:
In account B, open the Log groups page of the Amazon CloudWatch console.
Choose the log group for your function (/aws/lambda/Function-With-SNS).
Choose the most recent log stream.

If your function was correctly invoked, you’ll see output similar to the following showing the contents of the message you published to your topic.


2023-07-31T21:42:51.250Z c1cba6b8-ade9-4380-aa32-d1a225da0e48 INFO Processed message Hello World
2023-07-31T21:42:51.250Z c1cba6b8-ade9-4380-aa32-d1a225da0e48 INFO done

Clean up your resources

You can now delete the resources that you created for this tutorial, unless you want to retain them. By deleting AWS resources that you're no longer using, you prevent unnecessary charges to your AWS account.

In Account A, clean up your Amazon SNS topic.

To delete the Amazon SNS topic

Open the Topics page of the Amazon SNS console.
Select the topic you created.
Choose Delete.
Enter delete me in the text input field.
Choose Delete.

In Account B, clean up your execution role, Lambda function, and Amazon SNS subscription.

To delete the execution role

Open the Roles page of the IAM console.
Select the execution role that you created.
Choose Delete.
Enter the name of the role in the text input field and choose Delete.

To delete the Lambda function

Open the Functions page of the Lambda console.
Select the function that you created.
Choose Actions, Delete.
Type confirm in the text input field and choose Delete.

To delete the Amazon SNS subscription

Open the Subscriptions page of the Amazon SNS console.
Select the subscription you created.
Choose Delete, Delete.

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Document Conventions

SNS

Lambda permissions