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AWS Lambda Powertools Python

A suite of utilities for AWS Lambda functions to ease adopting best practices such as tracing, structured logging, custom metrics, and more.

!!! tip "Looking for a quick read through how the core features are used?" Check out this detailed blog post with a practical example.

Tenets

This project separates core utilities that will be available in other runtimes vs general utilities that might not be available across all runtimes.

  • AWS Lambda only. We optimise for AWS Lambda function environments and supported runtimes only. Utilities might work with web frameworks and non-Lambda environments, though they are not officially supported.
  • Eases the adoption of best practices. The main priority of the utilities is to facilitate best practices adoption, as defined in the AWS Well-Architected Serverless Lens; all other functionality is optional.
  • Keep it lean. Additional dependencies are carefully considered for security and ease of maintenance, and prevent negatively impacting startup time.
  • We strive for backwards compatibility. New features and changes should keep backwards compatibility. If a breaking change cannot be avoided, the deprecation and migration process should be clearly defined.
  • We work backwards from the community. We aim to strike a balance of what would work best for 80% of customers. Emerging practices are considered and discussed via Requests for Comment (RFCs)
  • Idiomatic. Utilities follow programming language idioms and language-specific best practices.

Install

Powertools is available in PyPi. You can use your favourite dependency management tool to install it

  • poetry: poetry add aws-lambda-powertools
  • pip: pip install aws-lambda-powertools

Quick hello world example using SAM CLI

=== "shell"

```bash
sam init --location https://github.com/aws-samples/cookiecutter-aws-sam-python
```

Lambda Layer

Powertools is also available as a Lambda Layer, and it is distributed via the AWS Serverless Application Repository (SAR) to support semantic versioning.

App ARN Description
aws-lambda-powertools-python-layer arn:aws:serverlessrepo:eu-west-1:057560766410:applications/aws-lambda-powertools-python-layer Core dependencies only; sufficient for nearly all utilities.
aws-lambda-powertools-python-layer-extras arn:aws:serverlessrepo:eu-west-1:057560766410:applications/aws-lambda-powertools-python-layer-extras Core plus extra dependencies such as pydantic that is required by parser utility.

!!! warning Layer-extras does not support Python 3.6 runtime. This layer also includes all extra dependencies: 22.4MB zipped, ~155MB unzipped.

If using SAM, you can include this SAR App as part of your shared Layers stack, and lock to a specific semantic version. Once deployed, it'll be available across the account this is deployed to.

=== "SAM"

```yaml hl_lines="5-6 12-13"
AwsLambdaPowertoolsPythonLayer:
    Type: AWS::Serverless::Application
    Properties:
    Location:
        ApplicationId: arn:aws:serverlessrepo:eu-west-1:057560766410:applications/aws-lambda-powertools-python-layer
        SemanticVersion: 1.17.0 # change to latest semantic version available in SAR

MyLambdaFunction:
    Type: AWS::Serverless::Function
    Properties:
    Layers:
        # fetch Layer ARN from SAR App stack output
        - !GetAtt AwsLambdaPowertoolsPythonLayer.Outputs.LayerVersionArn
```

=== "Serverless framework"

```yaml hl_lines="5 8 10-11"
functions:
    main:
    handler: lambda_function.lambda_handler
    layers:
        - !GetAtt AwsLambdaPowertoolsPythonLayer.Outputs.LayerVersionArn

resources:
    Transform: AWS::Serverless-2016-10-31
    Resources:
    AwsLambdaPowertoolsPythonLayer:
        Type: AWS::Serverless::Application
        Properties:
        Location:
            ApplicationId: arn:aws:serverlessrepo:eu-west-1:057560766410:applications/aws-lambda-powertools-python-layer
            # Find latest from github.com/awslabs/aws-lambda-powertools-python/releases
            SemanticVersion: 1.17.0
```

=== "CDK"

```python hl_lines="14 22-23 31"
from aws_cdk import core, aws_sam as sam, aws_lambda

POWERTOOLS_BASE_NAME = 'AWSLambdaPowertools'
# Find latest from github.com/awslabs/aws-lambda-powertools-python/releases
POWERTOOLS_VER = '1.17.0'
POWERTOOLS_ARN = 'arn:aws:serverlessrepo:eu-west-1:057560766410:applications/aws-lambda-powertools-python-layer'

class SampleApp(core.Construct):

    def __init__(self, scope: core.Construct, id_: str) -> None:
        super().__init__(scope, id_)

        # Launches SAR App as CloudFormation nested stack and return Lambda Layer
        powertools_app = sam.CfnApplication(self,
            f'{POWERTOOLS_BASE_NAME}Application',
            location={
                'applicationId': POWERTOOLS_ARN,
                'semanticVersion': POWERTOOLS_VER
            },
        )

        powertools_layer_arn = powertools_app.get_att("Outputs.LayerVersionArn").to_string()
        powertools_layer_version = aws_lambda.LayerVersion.from_layer_version_arn(self, f'{POWERTOOLS_BASE_NAME}', powertools_layer_arn)

        aws_lambda.Function(self,
            'sample-app-lambda',
            runtime=aws_lambda.Runtime.PYTHON_3_8,
            function_name='sample-lambda',
            code=aws_lambda.Code.asset('./src'),
            handler='app.handler',
            layers: [powertools_layer_version]
        )
```

??? tip "Example of least-privileged IAM permissions to deploy Layer"

> Credits to [mwarkentin](https://github.com/mwarkentin) for providing the scoped down IAM permissions.

The region and the account id for `CloudFormationTransform` and `GetCfnTemplate` are fixed.

=== "template.yml"

    ```yaml hl_lines="21-52"
    AWSTemplateFormatVersion: "2010-09-09"
    Resources:
        PowertoolsLayerIamRole:
        Type: "AWS::IAM::Role"
        Properties:
            AssumeRolePolicyDocument:
            Version: "2012-10-17"
            Statement:
                - Effect: "Allow"
                Principal:
                    Service:
                    - "cloudformation.amazonaws.com"
                Action:
                    - "sts:AssumeRole"
            Path: "/"
        PowertoolsLayerIamPolicy:
        Type: "AWS::IAM::Policy"
        Properties:
            PolicyName: PowertoolsLambdaLayerPolicy
            PolicyDocument:
            Version: "2012-10-17"
            Statement:
                - Sid: CloudFormationTransform
                Effect: Allow
                Action: cloudformation:CreateChangeSet
                Resource:
                    - arn:aws:cloudformation:us-east-1:aws:transform/Serverless-2016-10-31
                - Sid: GetCfnTemplate
                Effect: Allow
                Action:
                    - serverlessrepo:CreateCloudFormationTemplate
                    - serverlessrepo:GetCloudFormationTemplate
                Resource:
                    # this is arn of the powertools SAR app
                    - arn:aws:serverlessrepo:eu-west-1:057560766410:applications/aws-lambda-powertools-python-layer
                - Sid: S3AccessLayer
                Effect: Allow
                Action:
                    - s3:GetObject
                Resource:
                    # AWS publishes to an external S3 bucket locked down to your account ID
                    # The below example is us publishing lambda powertools
                    # Bucket: awsserverlessrepo-changesets-plntc6bfnfj
                    # Key: *****/arn:aws:serverlessrepo:eu-west-1:057560766410:applications-aws-lambda-powertools-python-layer-versions-1.10.2/aeeccf50-****-****-****-*********
                    - arn:aws:s3:::awsserverlessrepo-changesets-*/*
                - Sid: GetLayerVersion
                Effect: Allow
                Action:
                    - lambda:PublishLayerVersion
                    - lambda:GetLayerVersion
                Resource:
                    - !Sub arn:aws:lambda:${AWS::Region}:${AWS::AccountId}:layer:aws-lambda-powertools-python-layer*
            Roles:
            - Ref: "PowertoolsLayerIamRole"
    ```

You can fetch available versions via SAR API with:

=== "shell"

```bash
aws serverlessrepo list-application-versions \
    --application-id arn:aws:serverlessrepo:eu-west-1:057560766410:applications/aws-lambda-powertools-python-layer
```

Features

Utility Description
Tracing Decorators and utilities to trace Lambda function handlers, and both synchronous and asynchronous functions
Logger Structured logging made easier, and decorator to enrich structured logging with key Lambda context details
Metrics Custom Metrics created asynchronously via CloudWatch Embedded Metric Format (EMF)
Event handler: AppSync AppSync event handler for Lambda Direct Resolver and Amplify GraphQL Transformer function
Event handler: API Gateway and ALB Amazon API Gateway REST/HTTP API and ALB event handler for Lambda functions invoked using Proxy integration
Middleware factory Decorator factory to create your own middleware to run logic before, and after each Lambda invocation
Parameters Retrieve parameter values from AWS Systems Manager Parameter Store, AWS Secrets Manager, or Amazon DynamoDB, and cache them for a specific amount of time
Batch processing Handle partial failures for AWS SQS batch processing
Typing Static typing classes to speedup development in your IDE
Validation JSON Schema validator for inbound events and responses
Event source data classes Data classes describing the schema of common Lambda event triggers
Parser Data parsing and deep validation using Pydantic
Idempotency Idempotent Lambda handler
Feature Flags A simple rule engine to evaluate when one or multiple features should be enabled depending on the input

Environment variables

!!! info Explicit parameters take precedence over environment variables.

Environment variable Description Utility Default
POWERTOOLS_SERVICE_NAME Sets service name used for tracing namespace, metrics dimension and structured logging All "service_undefined"
POWERTOOLS_METRICS_NAMESPACE Sets namespace used for metrics Metrics None
POWERTOOLS_TRACE_DISABLED Explicitly disables tracing Tracing false
POWERTOOLS_TRACER_CAPTURE_RESPONSE Captures Lambda or method return as metadata. Tracing true
POWERTOOLS_TRACER_CAPTURE_ERROR Captures Lambda or method exception as metadata. Tracing true
POWERTOOLS_TRACE_MIDDLEWARES Creates sub-segment for each custom middleware Middleware factory false
POWERTOOLS_LOGGER_LOG_EVENT Logs incoming event Logging false
POWERTOOLS_LOGGER_SAMPLE_RATE Debug log sampling Logging 0
POWERTOOLS_LOG_DEDUPLICATION_DISABLED Disables log deduplication filter protection to use Pytest Live Log feature Logging false
POWERTOOLS_EVENT_HANDLER_DEBUG Enables debugging mode for event handler Event Handler false
LOG_LEVEL Sets logging level Logging INFO

Debug mode

As a best practice, AWS Lambda Powertools logging statements are suppressed. If necessary, you can enable debugging using set_package_logger:

=== "app.py"

```python
from aws_lambda_powertools.logging.logger import set_package_logger

set_package_logger()
```