# AWS Lambda Construct Library
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This construct library allows you to define AWS Lambda Functions.

```ts
import { aws_lambda as lambda } from 'aws-cdk-lib';
import * as path from 'path';

const fn = new lambda.Function(this, 'MyFunction', {
  runtime: lambda.Runtime.NODEJS_12_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](#bundling-asset-code).
 * `lambda.Code.fromDockerBuild(path, options)` - use the result of a Docker
   build as code. The runtime code is expected to be located at `/asset` in the
   image and will be zipped and uploaded to S3 as an asset.

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](test/integ.assets.lit.ts)

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.

## Docker Images

Lambda functions allow specifying their handlers within docker images. The docker
image can be an image from ECR or a local asset that the CDK will package and load
into ECR.

The following `DockerImageFunction` construct uses a local folder with a
Dockerfile as the asset that will be used as the function handler.

```ts
new lambda.DockerImageFunction(this, 'AssetFunction', {
  code: lambda.DockerImageCode.fromImageAsset(path.join(__dirname, 'docker-handler')),
});
```

You can also specify an image that already exists in ECR as the function handler.

```ts
import { aws_ecr as ecr } from 'aws-cdk-lib';
const repo = new ecr.Repository(this, 'Repository');

new lambda.DockerImageFunction(this, 'ECRFunction', {
  code: lambda.DockerImageCode.fromEcr(repo),
});
```

## 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:

```ts
const fn = new lambda.Function(this, 'MyFunction', {
  runtime: lambda.Runtime.NODEJS_12_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:

```ts
const fn = new lambda.Function(this, 'MyFunction', {
  runtime: lambda.Runtime.NODEJS_12_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](https://docs.aws.amazon.com/lambda/latest/dg/configuration-versions.html)
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](https://docs.aws.amazon.com/lambda/latest/dg/configuration-aliases.html)
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.
>
> An alternative to defining a `lambda.Version` is to set an environment variable
> which changes at least as often as your code does. This makes sure the function
> always has the latest code.
>
> ```ts
> const codeVersion = "stringOrMethodToGetCodeVersion";
> const fn = new lambda.Function(this, 'MyFunction', {
>  environment: {
>    'CodeVersionString': codeVersion
>  }
> });
> ```

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.

```ts
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](test/integ.layer-version.lit.ts)

By default, updating a layer creates a new layer version, and CloudFormation will delete the old version as part of the stack update.

Alternatively, a removal policy can be used to retain the old version:

```ts
import { LayerVersion } from 'aws-cdk-lib/aws-lambda';
new LayerVersion(this, 'MyLayer', {
  removalPolicy: RemovalPolicy.RETAIN
});
```

## Event Rule Target

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

```ts
import { aws_events_targets as targets } from 'aws-cdk-lib';
rule.addTarget(new targets.LambdaFunction(myFunction));
```

## Event Sources

AWS Lambda supports a [variety of event sources](https://docs.aws.amazon.com/lambda/latest/dg/invoking-lambda-function.html).

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:

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

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

```ts
import { S3EventSource } from 'aws-cdk-lib/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.

```ts
import { aws_lambda as lambda } from 'aws-cdk-lib';

const fn = new lambda.Function(this, 'MyFunction', {
    runtime: lambda.Runtime.NODEJS_12_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:

```ts
import { aws_lambda as lambda } from 'aws-cdk-lib';
import { aws_sqs as sqs } from 'aws-cdk-lib';

const dlq = new sqs.Queue(this, 'DLQ');
const fn = new lambda.Function(this, 'MyFunction', {
    runtime: lambda.Runtime.NODEJS_12_X,
    handler: 'index.handler',
    code: lambda.Code.fromInline('exports.handler = function(event, ctx, cb) { return cb(null, "hi"); }'),
    deadLetterQueue: dlq
});
```

See [the AWS documentation](https://docs.aws.amazon.com/lambda/latest/dg/dlq.html)
to learn more about AWS Lambdas and DLQs.

## Lambda with X-Ray Tracing

```ts
import { aws_lambda as lambda } from 'aws-cdk-lib';

const fn = new lambda.Function(this, 'MyFunction', {
    runtime: lambda.Runtime.NODEJS_12_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](https://docs.aws.amazon.com/lambda/latest/dg/lambda-x-ray.html)
to learn more about AWS Lambda's X-Ray support.

## Lambda with Profiling

The following code configures the lambda function with CodeGuru profiling. By default, this creates a new CodeGuru
profiling group -

```ts
import { aws_lambda as lambda } from 'aws-cdk-lib';

const fn = new lambda.Function(this, 'MyFunction', {
    runtime: lambda.Runtime.PYTHON_3_6,
    handler: 'index.handler',
    code: lambda.Code.fromAsset('lambda-handler'),
    profiling: true
});
```

The `profilingGroup` property can be used to configure an existing CodeGuru profiler group.

CodeGuru profiling is supported for all Java runtimes and Python3.6+ runtimes.

See [the AWS documentation](https://docs.aws.amazon.com/codeguru/latest/profiler-ug/setting-up-lambda.html)
to learn more about AWS Lambda's Profiling support.

## Lambda with Reserved Concurrent Executions

```ts
import { aws_lambda as lambda } from 'aws-cdk-lib';

const fn = new lambda.Function(this, 'MyFunction', {
    runtime: lambda.Runtime.NODEJS_12_X,
    handler: 'index.handler',
    code: lambda.Code.fromInline('exports.handler = function(event, ctx, cb) { return cb(null, "hi"); }'),
    reservedConcurrentExecutions: 100
});
```

See [the AWS documentation](https://docs.aws.amazon.com/lambda/latest/dg/concurrent-executions.html)
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:

```ts
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](test/integ.autoscaling.lit.ts)

See [the AWS documentation](https://docs.aws.amazon.com/lambda/latest/dg/invocation-scaling.html) 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](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-cfn-customresource.html) 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`.

```ts
// 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 environment
  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:

```ts
new lambda.Function(this, 'Function', {
  code: lambda.Code.fromAsset(path.join(__dirname, 'my-python-handler'), {
    bundling: {
      image: lambda.Runtime.PYTHON_3_8.bundlingImage,
      command: [
        'bash', '-c',
        'pip install -r requirements.txt -t /asset-output && cp -au . /asset-output'
      ],
    },
  }),
  runtime: lambda.Runtime.PYTHON_3_8,
  handler: 'index.handler',
});
```

Runtimes expose a `bundlingImage` property that points to the [AWS SAM](https://github.com/awslabs/aws-sam-cli) build image.

Use `cdk.DockerImage.fromRegistry(image)` to use an existing image or
`cdk.DockerImage.fromBuild(path)` to build a specific image:

```ts
import * as cdk from 'aws-cdk-lib';

new lambda.Function(this, 'Function', {
  code: lambda.Code.fromAsset('/path/to/handler', {
    bundling: {
      image: cdk.DockerImage.fromBuild('/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:

* `@aws-cdk/aws-lambda-nodejs`: [Github](https://github.com/aws/aws-cdk/tree/master/packages/%40aws-cdk/aws-lambda-nodejs) & [CDK Docs](https://docs.aws.amazon.com/cdk/api/latest/docs/aws-lambda-nodejs-readme.html)
* `@aws-cdk/aws-lambda-python`: [Github](https://github.com/aws/aws-cdk/tree/master/packages/%40aws-cdk/aws-lambda-python) & [CDK Docs](https://docs.aws.amazon.com/cdk/api/latest/docs/aws-lambda-python-readme.html)

## Code Signing

Code signing for AWS Lambda helps to ensure that only trusted code runs in your Lambda functions. 
When enabled, AWS Lambda checks every code deployment and verifies that the code package is signed by a trusted source.
For more information, see [Configuring code signing for AWS Lambda](https://docs.aws.amazon.com/lambda/latest/dg/configuration-codesigning.html).
The following code configures a function with code signing.

```typescript
import { aws_signer as signer } from 'aws-cdk-lib';

const signerProfile = signer.SigningProfile(this, 'SigningProfile', {
  platform: Platform.AWS_LAMBDA_SHA384_ECDSA
});

const codeSigningConfig = new lambda.CodeSigningConfig(stack, 'CodeSigningConfig', {
   signingProfiles: [signingProfile],
});

new lambda.Function(this, 'Function', {
   codeSigningConfig,
   // ...
});
```
