Invoking an AWS Lambda function from an Aurora PostgreSQL DB cluster

AWS Lambda is an event-driven compute service that lets you run code without provisioning or managing servers. It's available for use with many AWS services, including Aurora PostgreSQL. For example, you can use Lambda functions to process event notifications from a database, or to load data from files whenever a new file is uploaded to Amazon S3. To learn more about Lambda, see What is AWS Lambda? in the AWS Lambda Developer Guide.

Setting up Aurora PostgreSQL to work with Lambda functions is a multi-step process involving AWS Lambda, IAM, your VPC, and your Aurora PostgreSQL DB cluster. Following, you can find summaries of the necessary steps.

For more information about Lambda functions, see Getting started with Lambda and AWS Lambda foundations in the AWS Lambda Developer Guide.

Step 1: Configure your Aurora PostgreSQL DB cluster for outbound connections to AWS Lambda

Lambda functions always run inside an Amazon VPC that's owned by the AWS Lambda service. Lambda applies network access and security rules to this VPC and it maintains and monitors the VPC automatically. Your Aurora PostgreSQL DB cluster sends network traffic to the Lambda service's VPC. How you configure this depends on whether your Aurora DB cluster's primary DB instance is public or private.

Your VPC can now interact with the AWS Lambda VPC at the network level. Next, you configure the permissions using IAM.

Step 2: Configure IAM for your Aurora PostgreSQL DB cluster and AWS Lambda

Invoking Lambda functions from your Aurora PostgreSQL DB cluster requires certain privileges. To configure the necessary privileges, we recommend that you create an IAM policy that allows invoking Lambda functions, assign that policy to a role, and then apply the role to your DB cluster. This approach gives the DB cluster privileges to invoke the specified Lambda function on your behalf. The following steps show you how to do this using the AWS CLI.

With the VPC and the IAM configurations complete, you can now install the aws_lambda extension. (Note that you can install the extension at any time, but until you set up the correct VPC support and IAM privileges, the aws_lambda extension adds nothing to your Aurora PostgreSQL DB cluster's capabilities.)

Step 3: Install the aws_lambda extension for an Aurora PostgreSQL DB cluster

To use AWS Lambda with your Aurora PostgreSQL DB cluster, add the aws_lambda PostgreSQL extension to your Aurora PostgreSQL DB cluster. This extension provides your Aurora PostgreSQL DB cluster with the ability to call Lambda functions from PostgreSQL.

The aws_lambda extension is installed in your Aurora PostgreSQL DB cluster's primary DB instance. You can now create convenience structures for invoking your Lambda functions.

Step 4: Use Lambda helper functions with your Aurora PostgreSQL DB cluster (Optional)

You can use the helper functions in the aws_commons extension to prepare entities that you can more easily invoke from PostgreSQL. To do this, you need to have the following information about your Lambda functions:

To hold the Lambda function name information, you use the aws_commons.create_lambda_function_arn function. This helper function creates an aws_commons._lambda_function_arn_1 composite structure with the details needed by the invoke function. Following, you can find three alternative approaches to setting up this composite structure.

SELECT aws_commons.create_lambda_function_arn(
   'my-function',
   'aws-region'
) AS aws_lambda_arn_1 \gset

SELECT aws_commons.create_lambda_function_arn(
   '111122223333:function:my-function',
   'aws-region'
) AS lambda_partial_arn_1 \gset

SELECT aws_commons.create_lambda_function_arn(
   'arn:aws:lambda:aws-region:111122223333:function:my-function'
) AS lambda_arn_1 \gset

Any of these values can be used in calls to the aws_lambda.invoke function. For examples, see Step 5: Invoke a Lambda function from your Aurora PostgreSQL DB cluster.

Step 5: Invoke a Lambda function from your Aurora PostgreSQL DB cluster

The aws_lambda.invoke function behaves synchronously or asynchronously, depending on the invocation_type. The two alternatives for this parameter are RequestResponse (the default) and Event, as follows.

As a simple test of your setup, you can connect to your DB instance using psql and invoke an example function from the command line. Suppose that you have one of the basic functions set up on your Lambda service, such as the simple Python function shown in the following screenshot.

If your invocation attempt doesn't succeed, see Lambda function error messages .

Step 6: Grant other users permission to invoke Lambda functions

At this point in the procedures, only you as rds_superuser can invoke your Lambda functions. To allow other users to invoke any functions that you create, you need to grant them permission.