A first peek at Lambda Powertools

AWS Lambda Powertools for Python has been around publicly since the end of 2019 and reached General Availability in June 2020. It’s described as “A suite of utilities for AWS Lambda functions to ease adopting best practices such as tracing, structured logging, custom metrics, and more.”

Within the community, this library has become almost a standard for serverless projects and it is clear to see why. Over the past year the pace of features being added has rocketed; it has certainly become one of my favourite tools to have at my disposal when it comes to building serverless solutions on AWS.

In this post, we’ll look at my five favourite features of Lambda Powertools and how they can be used day-to-day to make development more efficient.

I’m deliberately not going to go into super detail on how to set up each of these features - the documentation is very, very good and there’s no need for me to repeat it all!

All the features discussed below are consolidated into a demo application on GitHub here.

Tracer

The Tracer utility is a light wrapper on top of AWS X-Ray, a service used for tracing requests through an application. Often these applications are microservice architectures where one request might touch many services behind the scenes. Having a way to debug where this request might’ve gone wrong along the road is incredibly useful.

The code snippets below shows what needs to be added to the SAM template and Lambda function Python script in order to get a minimal example up and running for tracing with X-Ray.

HelloWorldFunction:
  Type: AWS::Serverless::Function
  Properties:
    Tracing: Active
    Environment:
      Variables:
        POWERTOOLS_SERVICE_NAME: lambda-powertools-demo-hello-world

from aws_lambda_powertools import Tracer

tracer = Tracer()


@tracer.capture_lambda_handler
def lambda_handler(event, context):
    return {
        "statusCode": 200,
        "body": json.dumps({
            "message": "hello world",
        }),
    }

Once requests start running through the function, X-Ray will generate traces such as the one below.

Logger

Next up, it’s the Logger utility. We all know that logging in applications is important for debugging purposes as well as general observability. Within AWS, CloudWatch Logs is the obvious choice for log storage and searching. The Logger tool in Powertools makes writing structured logs considerably easier. When running a statement like logger.info("foo") the library will take care of writing to CloudWatch in a consistent format to make searching easy.

The snippets below show the basic steps required to get logging hooked up within your Lambda.

HelloWorldFunction:
  Type: AWS::Serverless::Function
  Properties:
    Environment:
      Variables:
        POWERTOOLS_SERVICE_NAME: lambda-powertools-demo-hello-world
        LOG_LEVEL: INFO

from aws_lambda_powertools import Logger

logger = Logger()


@logger.inject_lambda_context(log_event=True)
def lambda_handler(event, context):
    logger.info("Running Hello World function")
    return {
        "statusCode": 200,
        "body": json.dumps({
            "message": "hello world",
        }),
    }

The simple example above translates into a log stream like the following. You can see that the Lambda function event and the logger.info call have been written in a consistent format which makes it possible for us to query them using CloudWatch Log Insights - a service built on top of CloudWatch Logs that enables the understanding of logs through a structured query language.

Event Source Data Classes

Event Source Data Classes are an understated favourite. They don’t provide any interaction with AWS services, but they do increase the efficiency of developing event-driven applications.

They do this by providing documented, typed classes for a variety of events that can trigger a Lambda function. This means that when developing against these events, you don’t need to spend all the time with your head in documentation trying to figure out what parameters get sent and whether they are serialised or not.

import json
from aws_lambda_powertools import Logger
from aws_lambda_powertools.utilities.data_classes import (
    event_source,
    APIGatewayProxyEvent
)


logger = Logger()


@event_source(data_class=APIGatewayProxyEvent)
@logger.inject_lambda_context(log_event=True)
def lambda_handler(event: APIGatewayProxyEvent, context):
    logger.info(f"Method: {event.http_method}")
    logger.info(f"Path: {event.path}")

    return {
        "statusCode": 200,
        "body": json.dumps({
            "message": "hello world",
        }),
    }