@ixor/aws-cdk-ixor-lambda module

Overview

+----+ Ixor Lambda Construct+----------------------------------+
|                                                              |
| +--------------------+   +---------------------------------+ |
| |                    |   |                                 | |
| | CW Event Rule      |   | Lambda Function                 | |
| |                    |   |                                 | |
| |                    |   | if (event.dummy) {              | |
| |{                   |   |   sleep(event.dummySleepSeconds | |
| |  "count": 2,       |   |   return({})                    | |
| |  "lambdaArn": "arn"|   | }                               | |
| |}                   |   | ...                             | |
| |                    |   |                                 | |
| +---------------+----+   +---^-----------------------------+ |
|                 |            |                               |
+--------------------------------------------------------------+
                  |            +
                  |         count times
                  |            |
                  |            |
            +-----v------------+---------+
            |                            |
            |  keepWarmLambdaFunction    |
            |                            |
            |  {                         |
            |    "dummy": "dummy",       |
            |    "dummySleepSeconds": 1  |
            |  }                         |
            +----------------------------+

This is a aws-cdk construct that extends the default Lambda Function class with keepWarm functionality.

The Function class can have 4 optional properties that configure the keepWarm behaviour of the function:

interface IxorLambdaFunctionProps extends lambda.FunctionProps {
      keepWarm?: boolean,
      keepWarmEventSchedule?: events.Schedule,
      keepWarmLambdaFunction?: lambda.IFunction,
      keepWarmCount?: number
}

When keepWarm is true, the keepWarmLambdaFunction is required.

keepWarmCount defaults to 2 is not specified.

keepWarmEventSchedule defaults to business hours.

Prerequisite: the keep warm lambda function

This function should already exist in the AWS account. It is triggered by the CloudWatch rule with an event that looks like this:

{
  "count": 2,
  "lambdaArn": "arn-of-the-lambda-function-to-keep-warm"
}

The function should have invoke permissions on all Lambda's to keep warm, and it will asynchonously invoke the function in lambdaArn count times.

This is an implementation of the keep warm Lambda, it is also available on npm.

import json
import logging
import boto3
import os

logger = logging.getLogger()
logger.setLevel(logging.INFO)

client = boto3.client("lambda")

dummy_sleep_seconds = os.getenv('DUMMY_SLEEP_SECONDS', '1')

def lambda_handler(event, context):
    logger.info(json.dumps(event))
    count = event.get('count', 3)
    lambda_arn = event.get('lambdaArn')
    logger.debug(f"Lambda to warm: {lambda_arn}")
    logger.debug(f"How many? {count}")
    logger.info(f"Asynchronously starting {count} target lambdas")

    success_count = 0

    for i in range(count):
        logger.debug(f"Iteration {i+1}")
        try:
            client.invoke(
                FunctionName=lambda_arn,
                InvocationType='Event',
                Payload=f'{{"dummy": "dummy", "dummySleepSeconds": {dummy_sleep_seconds} }}'
            )
        except Exception as e:
            logger.error(f"Exception occured: {e}")
        else:
            success_count = success_count + 1

    logger.info(f"{success_count}/{count} successful invocations")

    return {
        'statusCode': 200,
        'body': json.dumps('Finished')
    }

How it works

The construct creates 2 resources:

• A CloudWatch rule
• The Lambda function (that optionally needs to be kept Warm)

The CloudWatch rule

The CloudWatch rule is configured to start the keep warm Lambda function with a preconfigured event. The event has 2 required properties:

• count: How many instances of the target Lambda to try to keep warm
• lambdaArn: The ARN of the Lambda function to keep warm

The Lambda Function

The Lambda function is created as documented in the AWS CDK Lambda Function class. But in order to be kept warm, the function should be able to process a dummy event. The keep warm lambda function (see the prerequisite section) will invoke the function with a dummy event that looks like this:

{
  "dummy": "dummy",
  "dummySleepSeconds": 1
}

The Lambda function should check for the dummy event and sleep the requested amount of time (in seconds).

Testing

A test stack is added in lib\test-aws-cdk-ixor-lambda-stack. Created in this stack:

• keepWarmLambda: this lambda will send out a dummy event every 10 minutes.
• lambdaToKeepWarm: this is a lambda created through the IxorFunction and needs to be kept warm
• The appropriate permissions for the keepWarmLambda to invoke the lambdaToKeepWarm.

The code for both lambdas is situated in the test_aws_cdk_ixor_lambda_handler directory.

To test this stack, deploy the test/test-aws-cdk-ixor-lambda app to sandbox. Every 10 minutes, the keepWarm lambda will trigger the lambdaToKeepWarm with a dummy event, both log this in CloudWatch.