@aws-cdk/aws-lambda

AWS Lambda Construct Library

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This construct library allows you to define AWS Lambda Functions.

import * as lambda from '@aws-cdk/aws-lambda';
import * as path from 'path';

const fn = new lambda.Function(this, 'MyFunction', {
  runtime: lambda.Runtime.NODEJS_10_X,
  handler: 'index.handler',
  code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')),
});

Handler Code

The lambda.Code class includes static convenience methods for various types of runtime code.

• lambda.Code.fromBucket(bucket, key[, objectVersion]) - specify an S3 object that contains the archive of your runtime code.
• lambda.Code.fromInline(code) - inline the handle code as a string. This is limited to supported runtimes and the code cannot exceed 4KiB.
• lambda.Code.fromAsset(path) - specify a directory or a .zip file in the local filesystem which will be zipped and uploaded to S3 before deployment. See also bundling asset code.

The following example shows how to define a Python function and deploy the code from the local directory my-lambda-handler to it:

Example of Lambda Code from Local Assets

When deploying a stack that contains this code, the directory will be zip archived and then uploaded to an S3 bucket, then the exact location of the S3 objects will be passed when the stack is deployed.

During synthesis, the CDK expects to find a directory on disk at the asset directory specified. Note that we are referencing the asset directory relatively to our CDK project directory. This is especially important when we want to share this construct through a library. Different programming languages will have different techniques for bundling resources into libraries.

Execution Role

Lambda functions assume an IAM role during execution. In CDK by default, Lambda functions will use an autogenerated Role if one is not provided.

The autogenerated Role is automatically given permissions to execute the Lambda function. To reference the autogenerated Role:

const fn = new lambda.Function(this, 'MyFunction', {
  runtime: lambda.Runtime.NODEJS_10_X,
  handler: 'index.handler',
  code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')),

fn.role // the Role

You can also provide your own IAM role. Provided IAM roles will not automatically be given permissions to execute the Lambda function. To provide a role and grant it appropriate permissions:

const fn = new lambda.Function(this, 'MyFunction', {
  runtime: lambda.Runtime.NODEJS_10_X,
  handler: 'index.handler',
  code: lambda.Code.fromAsset(path.join(__dirname, 'lambda-handler')),
  role: myRole // user-provided role
});

myRole.addManagedPolicy(ManagedPolicy.fromAwsManagedPolicyName("service-role/AWSLambdaBasicExecutionRole"));
myRole.addManagedPolicy(ManagedPolicy.fromAwsManagedPolicyName("service-role/AWSLambdaVPCAccessExecutionRole")); // only required if your function lives in a VPC

Versions and Aliases

You can use versions to manage the deployment of your AWS Lambda functions. For example, you can publish a new version of a function for beta testing without affecting users of the stable production version.

The function version includes the following information:

• The function code and all associated dependencies.
• The Lambda runtime that executes the function.
• All of the function settings, including the environment variables.
• A unique Amazon Resource Name (ARN) to identify this version of the function.

You can define one or more aliases for your AWS Lambda function. A Lambda alias is like a pointer to a specific Lambda function version. Users can access the function version using the alias ARN.

The fn.currentVersion property can be used to obtain a lambda.Version resource that represents the AWS Lambda function defined in your application. Any change to your function's code or configuration will result in the creation of a new version resource. You can specify options for this version through the currentVersionOptions property.

The currentVersion property is only supported when your AWS Lambda function uses either lambda.Code.fromAsset or lambda.Code.fromInline. Other types of code providers (such as lambda.Code.fromBucket) require that you define a lambda.Version resource directly since the CDK is unable to determine if their contents had changed.

The version.addAlias() method can be used to define an AWS Lambda alias that points to a specific version.

The following example defines an alias named live which will always point to a version that represents the function as defined in your CDK app. When you change your lambda code or configuration, a new resource will be created. You can specify options for the current version through the currentVersionOptions property.

const fn = new lambda.Function(this, 'MyFunction', {
  currentVersionOptions: {
    removalPolicy: RemovalPolicy.RETAIN, // retain old versions
    retryAttempts: 1                     // async retry attempts
  }
});

fn.currentVersion.addAlias('live');

NOTE: The fn.latestVersion property returns a lambda.IVersion which represents the $LATEST pseudo-version. Most AWS services require a specific AWS Lambda version, and won't allow you to use $LATEST. Therefore, you would normally want to use lambda.currentVersion.

Layers

The lambda.LayerVersion class can be used to define Lambda layers and manage granting permissions to other AWS accounts or organizations.

Example of Lambda Layer usage

Event Rule Target

You can use an AWS Lambda function as a target for an Amazon CloudWatch event rule:

import * as targets from '@aws-cdk/aws-events-targets';
rule.addTarget(new targets.LambdaFunction(myFunction));

Event Sources

AWS Lambda supports a variety of event sources.

In most cases, it is possible to trigger a function as a result of an event by using one of the add<Event>Notification methods on the source construct. For example, the s3.Bucket construct has an onEvent method which can be used to trigger a Lambda when an event, such as PutObject occurs on an S3 bucket.

An alternative way to add event sources to a function is to use function.addEventSource(source). This method accepts an IEventSource object. The module @aws-cdk/aws-lambda-event-sources includes classes for the various event sources supported by AWS Lambda.

For example, the following code adds an SQS queue as an event source for a function:

import { SqsEventSource } from '@aws-cdk/aws-lambda-event-sources';
fn.addEventSource(new SqsEventSource(queue));

The following code adds an S3 bucket notification as an event source:

import { S3EventSource } from '@aws-cdk/aws-lambda-event-sources';
fn.addEventSource(new S3EventSource(bucket, {
  events: [ s3.EventType.OBJECT_CREATED, s3.EventType.OBJECT_DELETED ],
  filters: [ { prefix: 'subdir/' } ] // optional
}));

See the documentation for the @aws-cdk/aws-lambda-event-sources module for more details.

Lambda with DLQ

A dead-letter queue can be automatically created for a Lambda function by setting the deadLetterQueueEnabled: true configuration.

import * as lambda from '@aws-cdk/aws-lambda';

const fn = new lambda.Function(this, 'MyFunction', {
    runtime: lambda.Runtime.NODEJS_10_X,
    handler: 'index.handler',
    code: lambda.Code.fromInline('exports.handler = function(event, ctx, cb) { return cb(null, "hi"); }'),
    deadLetterQueueEnabled: true
});

It is also possible to provide a dead-letter queue instead of getting a new queue created:

import * as lambda from '@aws-cdk/aws-lambda';
import * as sqs from '@aws-cdk/aws-sqs';

const dlq = new sqs.Queue(this, 'DLQ');
const fn = new lambda.Function(this, 'MyFunction', {
    runtime: lambda.Runtime.NODEJS_10_X,
    handler: 'index.handler',
    code: lambda.Code.fromInline('exports.handler = function(event, ctx, cb) { return cb(null, "hi"); }'),
    deadLetterQueue: dlq
});

See the AWS documentation to learn more about AWS Lambdas and DLQs.

Lambda with X-Ray Tracing

import * as lambda from '@aws-cdk/aws-lambda';

const fn = new lambda.Function(this, 'MyFunction', {
    runtime: lambda.Runtime.NODEJS_10_X,
    handler: 'index.handler',
    code: lambda.Code.fromInline('exports.handler = function(event, ctx, cb) { return cb(null, "hi"); }'),
    tracing: lambda.Tracing.ACTIVE
});

See the AWS documentation to learn more about AWS Lambda's X-Ray support.

Lambda with Profiling

import * as lambda from '@aws-cdk/aws-lambda';

const fn = new lambda.Function(this, 'MyFunction', {
    runtime: lambda.Runtime.NODEJS_10_X,
    handler: 'index.handler',
    code: lambda.Code.fromInline('exports.handler = function(event, ctx, cb) { return cb(null, "hi"); }'),
    profiling: true
});

See the AWS documentation to learn more about AWS Lambda's Profiling support.

Lambda with Reserved Concurrent Executions

import * as lambda from '@aws-cdk/aws-lambda';

const fn = new lambda.Function(this, 'MyFunction', {
    runtime: lambda.Runtime.NODEJS_10_X,
    handler: 'index.handler',
    code: lambda.Code.fromInline('exports.handler = function(event, ctx, cb) { return cb(null, "hi"); }'),
    reservedConcurrentExecutions: 100
});

See the AWS documentation managing concurrency.

AutoScaling

You can use Application AutoScaling to automatically configure the provisioned concurrency for your functions. AutoScaling can be set to track utilization or be based on a schedule. To configure AutoScaling on a function alias:

const alias = new lambda.Alias(stack, 'Alias', {
  aliasName: 'prod',
  version,
});

// Create AutoScaling target
const as = alias.addAutoScaling({ maxCapacity: 50 })

// Configure Target Tracking
as.scaleOnUtilization({
  utilizationTarget: 0.5,
});

// Configure Scheduled Scaling
as.scaleOnSchedule('ScaleUpInTheMorning', {
  schedule: appscaling.Schedule.cron({ hour: '8', minute: '0'}),
  minCapacity: 20,
});

Example of Lambda AutoScaling usage

See the AWS documentation on autoscaling lambda functions.

Log Group

Lambda functions automatically create a log group with the name /aws/lambda/<function-name> upon first execution with log data set to never expire.

The logRetention property can be used to set a different expiration period.

It is possible to obtain the function's log group as a logs.ILogGroup by calling the logGroup property of the Function construct.

By default, CDK uses the AWS SDK retry options when creating a log group. The logRetentionRetryOptions property allows you to customize the maximum number of retries and base backoff duration.

Note that, if either logRetention is set or logGroup property is called, a CloudFormation custom resource is added to the stack that pre-creates the log group as part of the stack deployment, if it already doesn't exist, and sets the correct log retention period (never expire, by default).

Further note that, if the log group already exists and the logRetention is not set, the custom resource will reset the log retention to never expire even if it was configured with a different value.

FileSystem Access

You can configure a function to mount an Amazon Elastic File System (Amazon EFS) to a directory in your runtime environment with the filesystem property. To access Amazon EFS from lambda function, the Amazon EFS access point will be required.

The following sample allows the lambda function to mount the Amazon EFS access point to /mnt/msg in the runtime environment and access the filesystem with the POSIX identity defined in posixUser.

// create a new Amazon EFS filesystem
const fileSystem = new efs.FileSystem(stack, 'Efs', { vpc });

// create a new access point from the filesystem
const accessPoint = fileSystem.addAccessPoint('AccessPoint', {
  // set /export/lambda as the root of the access point
  path: '/export/lambda',
  // as /export/lambda does not exist in a new efs filesystem, the efs will create the directory with the following createAcl
  createAcl: {
    ownerUid: '1001',
    ownerGid: '1001',
    permissions: '750',
  },
  // enforce the POSIX identity so lambda function will access with this identity
  posixUser: {
    uid: '1001',
    gid: '1001',
  },
});

const fn = new lambda.Function(stack, 'MyLambda', {
  code,
  handler,
  runtime,
  vpc,
  // mount the access point to /mnt/msg in the lambda runtime enironment
  filesystem: lambda.FileSystem.fromEfsAccessPoint(accessPoint, '/mnt/msg'),
});

Singleton Function

The SingletonFunction construct is a way to guarantee that a lambda function will be guaranteed to be part of the stack, once and only once, irrespective of how many times the construct is declared to be part of the stack. This is guaranteed as long as the uuid property and the optional lambdaPurpose property stay the same whenever they're declared into the stack.

A typical use case of this function is when a higher level construct needs to declare a Lambda function as part of it but needs to guarantee that the function is declared once. However, a user of this higher level construct can declare it any number of times and with different properties. Using SingletonFunction here with a fixed uuid will guarantee this.

For example, the LogRetention construct requires only one single lambda function for all different log groups whose retention it seeks to manage.

Bundling Asset Code

When using lambda.Code.fromAsset(path) it is possible to bundle the code by running a command in a Docker container. The asset path will be mounted at /asset-input. The Docker container is responsible for putting content at /asset-output. The content at /asset-output will be zipped and used as Lambda code.

Example with Python:

new lambda.Function(this, 'Function', {
  code: lambda.Code.fromAsset(path.join(__dirname, 'my-python-handler'), {
    bundling: {
      image: lambda.Runtime.PYTHON_3_6.bundlingDockerImage,
      command: [
        'bash', '-c', `
        pip install -r requirements.txt -t /asset-output &&
        cp -au . /asset-output
        `,
      ],
    },
  }),
  runtime: lambda.Runtime.PYTHON_3_6,
  handler: 'index.handler',
});

Runtimes expose a bundlingDockerImage property that points to the AWS SAM build image.

Use cdk.BundlingDockerImage.fromRegistry(image) to use an existing image or cdk.BundlingDockerImage.fromAsset(path) to build a specific image:

import * as cdk from '@aws-cdk/core';

new lambda.Function(this, 'Function', {
  code: lambda.Code.fromAsset('/path/to/handler', {
    bundling: {
      image: cdk.BundlingDockerImage.fromAsset('/path/to/dir/with/DockerFile', {
        buildArgs: {
          ARG1: 'value1',
        },
      }),
      command: ['my', 'cool', 'command'],
    },
  }),
  // ...
});

Language-specific APIs

Language-specific higher level constructs are provided in separate modules:

• Node.js: @aws-cdk/aws-lambda-nodejs
• Python: @aws-cdk/aws-lambda-python