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Using AWS Lambda Destinations with Java

Alvaro

·

Source Lambda

The source lambda is the first lambda that will be called, either by an api call, a time event, a queue message or anything else that AWS Lambdas have support for.

The return time of this message (InterLambdaMessage) can be any serializable plain object with attributes with valid JSON types (string, numbers, boolean, arrays, objects and null).

package br.com.loom.source;

import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;

import java.util.Date;

public class SourceLambda implements RequestHandler<SourceMessage, InterLambdaMessage> {

    @Override
    public InterLambdaMessage handleRequest(SourceMessage event, Context context) {
        return new InterLambdaMessage()
                .setMessage("Message")
                .setData(new Date())
                .setFlag(true)
                .setNumber(1023L);
    }
}

Destination Lambda

The destination lambda is the lambda that will receive the message from the source lambda. It can return any type (same limitations of the source lambda) but the received message have a more specific structure.

package br.com.loom.destination;

import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;

public class DestinationLambda implements RequestHandler<EnvelopeMessage, String> {

    @Override
    public String handleRequest(EnvelopeMessage event, Context context) {
        return "ok";
    }
}

The received message have the following structure in the JSON level

{
	"version": "1.0",
	"timestamp": "2020-09-30T14:55:17.029Z",
	"requestContext": {
		"requestId": "some-uuid",
		"functionArn": "arn:aws:lambda:eu-west-1:account:function:source:$LATEST",
		"condition": "Success",
		"approximateInvokeCount": 1
       },
	"requestPayload": {<A>},
	"responseContext": {
		"statusCode": 200,
		"executedVersion": "$LATEST"
   },
	"responsePayload": {<B>}
}
  • <A> is a structured that dependes on the event that called the source lambda
  • <B> is the data that you returned in the source lambda

To receive that data you gonna need an Class like the one below. Notice that the object returned by the SourceLambda is a field called responsePayload in this object.

package br.com.loom.destination;

import lombok.Data;
import lombok.experimental.Accessors;

@Data
@Accessors(chain = true)
public class EnvelopeMessage {
    String version;
    String timestamp;
    InterLambdaMessage responsePayload;
}

Destination Configuration

Start by deploying the source lambda (using the normal way you already use) and click on the +Add destination button in the right.

Select the “Asynchronous invocation” source and either On Failure or On Success depending on what event you want to capture. Choose the “Destination Type” as “Lambda function”.

Finally select the destination lambda in the “Destination” drop box or type the ARN for the destination lambda.

A policy is required to make the call, but if you own both lambdas AWS offer to fix this for you.

If you need to set it up manually you will want something like this.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": "lambda:InvokeFunction",
            "Resource": "arn:aws:lambda:eu-west-1:1234567890:function:destination*"
        }
    ]
}

Testing the Destination

One important thing here, to test the destination the Test button doesn’t work. To test the configuration you will need to make a call using some controlled Event or using the aws CLI. 

aws lambda invoke --function-name source-lambda --invocation-type Event --payload '{ "time": "2020-09-30T18:25:43.511Z" }' response.json

If the call worked you will see this message after. 

{
    "StatusCode": 202
}

CloudFormation Template

If you are using the CloudFormation templates the destination will be configured as a separate resource rather than an item in the Lambda itself.

In the highlighted lines below we have the resource added to achieve the same as the configuration above.

AWSTemplateFormatVersion: 2010-09-09
Transform: AWS::Serverless-2016-10-31
Description: 

Resources:
  SourceLambda:
    Type: AWS::Serverless::Function
    Properties:
      FunctionName: source-lambda
      CodeUri: ../../source-lambda/build/distributions/source-lambda.zip
      Handler: br.com.loom.source.SourceLambda::handleRequest
      Runtime: java11
      MemorySize: 512
      Timeout: 900
  DestinationLambda:
    Type: AWS::Serverless::Function
    Properties:
      FunctionName: destination-lambda
      CodeUri: ../../destination-lambda/build/distributions/destination-lambda.zip
      Handler: br.com.loom.destination.DestinationLambda::handleRequest
      Runtime: java11
      MemorySize: 512
      Timeout: 900
  EventInvokeConfig:
    Type: AWS::Lambda::EventInvokeConfig
    Properties:
      FunctionName: !Ref SourceLambda
      Qualifier: "$LATEST"
      MaximumEventAgeInSeconds: 600
      MaximumRetryAttempts: 0
      DestinationConfig:
        OnSuccess:
          Destination: !GetAtt DestinationLambda.Arn
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