Amazon Lambda Destinations Library

This library provides constructs for adding destinations to a Lambda function. Destinations can be added by specifying the on_failure or on_success props when creating a function or alias.

Destinations

The following destinations are supported

• Lambda function
• SQS queue - Only standard SQS queues are supported for failure destinations, FIFO queues are not supported.
• SNS topic
• EventBridge event bus
• S3 bucket

Example with a SNS topic for successful invocations:

# An sns topic for successful invocations of a lambda function
require 'aws-cdk-lib'


my_topic = AWSCDK::SNS::Topic.new(self, "Topic")

my_fn = AWSCDK::Lambda::Function.new(self, "Fn", {
    runtime: AWSCDK::Lambda::Runtime.NODEJS_LATEST,
    handler: "index.handler",
    code: AWSCDK::Lambda::Code.from_asset(path.join(__dirname, "lambda-handler")),
    # sns topic for successful invocations
    on_success: AWSCDK::LambdaDestinations::SNSDestination.new(my_topic),
})

Example with a SQS queue for unsuccessful invocations:

# An sqs queue for unsuccessful invocations of a lambda function
require 'aws-cdk-lib'


dead_letter_queue = AWSCDK::SQS::Queue.new(self, "DeadLetterQueue")

my_fn = AWSCDK::Lambda::Function.new(self, "Fn", {
    runtime: AWSCDK::Lambda::Runtime.NODEJS_LATEST,
    handler: "index.handler",
    code: AWSCDK::Lambda::Code.from_inline("// your code"),
    # sqs queue for unsuccessful invocations
    on_failure: AWSCDK::LambdaDestinations::SQSDestination.new(dead_letter_queue),
})

See also Configuring Destinations for Asynchronous Invocation.

Invocation record

When a lambda function is configured with a destination, an invocation record is created by the Lambda service when the lambda function completes. The invocation record contains the details of the function, its context, and the request and response payloads.

The following example shows the format of the invocation record for a successful invocation:

{
    "version": "1.0",
    "timestamp": "2019-11-24T23:08:25.651Z",
    "requestContext": {
        "requestId": "c2a6f2ae-7dbb-4d22-8782-d0485c9877e2",
        "functionArn": "arn:aws:lambda:sa-east-1:123456789123:function:event-destinations:$LATEST",
        "condition": "Success",
        "approximateInvokeCount": 1
    },
    "requestPayload": {
        "Success": true
    },
    "responseContext": {
        "statusCode": 200,
        "executedVersion": "$LATEST"
    },
    "responsePayload": "<data returned by the function here>"
}

In case of failure, the record contains the reason and error object:

{
  "version": "1.0",
  "timestamp": "2019-11-24T21:52:47.333Z",
  "requestContext": {
    "requestId": "8ea123e4-1db7-4aca-ad10-d9ca1234c1fd",
    "functionArn": "arn:aws:lambda:sa-east-1:123456678912:function:event-destinations:$LATEST",
    "condition": "RetriesExhausted",
    "approximateInvokeCount": 3
  },
  "requestPayload": {
    "Success": false
  },
  "responseContext": {
    "statusCode": 200,
    "executedVersion": "$LATEST",
    "functionError": "Handled"
  },
  "responsePayload": {
    "errorMessage": "Failure from event, Success = false, I am failing!",
    "errorType": "Error",
    "stackTrace": [ "exports.handler (/var/task/index.js:18:18)" ]
  }
}

Destination-specific JSON format

• For SNS/SQS (SnsDestionation/SqsDestination), the invocation record JSON is passed as the Message to the destination.
• For Lambda (LambdaDestination), the invocation record JSON is passed as the payload to the function.
• For EventBridge (EventBridgeDestination), the invocation record JSON is passed as the detail in the PutEvents call. The value for the event field source is lambda, and the value for the event field detail-type is either 'Lambda Function Invocation Result - Success' or 'Lambda Function Invocation Result – Failure', depending on whether the lambda function invocation succeeded or failed. The event field resource contains the function and destination ARNs. See AWS Events for the different event fields.
• For S3 (S3Destination), the invocation record json is stored as a File in the destination bucket. The path of a destination payload file in the configured bucket is aws/lambda/async/<function-name>/YYYY/MM/DD/YYYY-MM-DDTHH.MM.SS-<Random UUID>.

Auto-extract response payload with lambda destination

The response_only option of LambdaDestination allows to auto-extract the response payload from the invocation record:

# Auto-extract response payload with a lambda destination
destination_fn = nil # AWSCDK::Lambda::Function


source_fn = AWSCDK::Lambda::Function.new(self, "Source", {
    runtime: AWSCDK::Lambda::Runtime.NODEJS_LATEST,
    handler: "index.handler",
    code: AWSCDK::Lambda::Code.from_asset(path.join(__dirname, "lambda-handler")),
    # auto-extract on success
    on_success: AWSCDK::LambdaDestinations::LambdaDestination.new(destination_fn, {
        response_only: true,
    }),
})

In the above example, destination_fn will be invoked with the payload returned by source_fn (response_payload in the invocation record, not the full record).

When used with on_failure, the destination function is invoked with the error object returned by the source function.

Using the response_only option allows to easily chain asynchronous Lambda functions without having to deal with data extraction in the runtime code.