Examples: Invoking Lambda functions from your RDS for PostgreSQL DB instance

Following, you can find several examples of calling the aws_lambda.invoke function. Most of the examples use the composite structure aws_lambda_arn_1 that you create in Step 4: Use Lambda helper functions with your RDS for PostgreSQL DB instance (Optional) to simplify passing the function details. For an example of asynchronous invocation, see Example: Asynchronous (Event) invocation of Lambda functions. All the other examples listed use synchronous invocation.

To learn more about Lambda invocation types, see Invoking Lambda functions in the AWS Lambda Developer Guide. For more information about aws_lambda_arn_1, see aws_commons.create_lambda_function_arn.

Example: Synchronous (RequestResponse) invocation of Lambda functions

Following are two examples of a synchronous Lambda function invocation. The results of these aws_lambda.invoke function calls are the same.

SELECT * FROM aws_lambda.invoke('aws_lambda_arn_1', '{"body": "Hello from Postgres!"}'::json);

SELECT * FROM aws_lambda.invoke('aws_lambda_arn_1', '{"body": "Hello from Postgres!"}'::json, 'RequestResponse');

The parameters are described as follows:

• :'aws_lambda_arn_1' – This parameter identifies the composite structure created in Step 4: Use Lambda helper functions with your RDS for PostgreSQL DB instance (Optional), with the aws_commons.create_lambda_function_arn helper function. You can also create this structure inline within your aws_lambda.invoke call as follows.

  SELECT * FROM aws_lambda.invoke(aws_commons.create_lambda_function_arn('my-function', 'aws-region'),
  '{"body": "Hello from Postgres!"}'::json
  );

• '{"body": "Hello from PostgreSQL!"}'::json – The JSON payload to pass to the Lambda function.

• 'RequestResponse' – The Lambda invocation type.

Example: Asynchronous (Event) invocation of Lambda functions

Following is an example of an asynchronous Lambda function invocation. The Event invocation type schedules the Lambda function invocation with the specified input payload and returns immediately. Use the Event invocation type in certain workflows that don't depend on the results of the Lambda function.

SELECT * FROM aws_lambda.invoke('aws_lambda_arn_1', '{"body": "Hello from Postgres!"}'::json, 'Event');

Example: Capturing the Lambda execution log in a function response

You can include the last 4 KB of the execution log in the function response by using the log_type parameter in your aws_lambda.invoke function call. By default, this parameter is set to None, but you can specify Tail to capture the results of the Lambda execution log in the response, as shown following.

SELECT *, select convert_from(decode(log_result, 'base64'), 'utf-8') as log FROM aws_lambda.invoke(:'aws_lambda_arn_1', '{"body": "Hello from Postgres!"}'::json, 'RequestResponse', 'Tail');

Set the aws_lambda.invoke function's log_type parameter to Tail to include the execution log in the response. The default value for the log_type parameter is None.

The log_result that's returned is a base64 encoded string. You can decode the contents using a combination of the decode and convert_from PostgreSQL functions.

For more information about log_type, see aws_lambda.invoke.

Example: Including client context in a Lambda function

The aws_lambda.invoke function has a context parameter that you can use to pass information separate from the payload, as shown following.

SELECT *, convert_from(decode(log_result, 'base64'), 'utf-8') as log FROM aws_lambda.invoke(:'aws_lambda_arn_1', '{"body": "Hello from Postgres!"}'::json, 'RequestResponse', 'Tail');

To include client context, use a JSON object for the aws_lambda.invoke function's context parameter.

For more information about the context parameter, see the aws_lambda.invoke reference.

Example: Invoking a specific version of a Lambda function

You can specify a particular version of a Lambda function by including the qualifier parameter with the aws_lambda.invoke call. Following, you can find an example that does this using 'custom_version' as an alias for the version.

SELECT * FROM aws_lambda.invoke('aws_lambda_arn_1', '{"body": "Hello from Postgres!"}'::json, 'RequestResponse', 'None', NULL, 'custom_version');

You can also supply a Lambda function qualifier with the function name details instead, as follows.

SELECT * FROM aws_lambda.invoke(aws_commons.create_lambda_function_arn('my-function:custom_version', 'us-west-2'),
'{"body": "Hello from Postgres!"}'::json);

For more information about qualifier and other parameters, see the aws_lambda.invoke reference.