Spring Integration Extension for Amazon Web Services (AWS)

Introduction

Amazon Web Services (AWS)

Launched in 2006, Amazon Web Services (AWS) provides key infrastructure services for business through its cloud computing platform. Using cloud computing businesses can adopt a new business model whereby they do not have to plan and invest in procuring their own IT infrastructure. They can use the infrastructure and services provided by the cloud service provider and pay as they use the services. Visit http://aws.amazon.com/products/ for more details about various products offered by Amazon as a part their cloud computing services.

Spring Integration Extension for Amazon Web Services provides Spring Integration adapters for the various services provided by the AWS SDK for Java. Note the Spring Integration AWS Extension is based on the Spring Cloud AWS project.

Spring Integration's extensions to AWS

This guide intends to explain briefly the various adapters available for Amazon Web Services such as:

• Amazon Simple Email Service (SES)
• Amazon Simple Storage Service (S3)
• Amazon Simple Queue Service (SQS)
• Amazon Simple Notification Service (SNS)
• Amazon DynamoDB (Analysis ongoing)
• Amazon SimpleDB (Not initiated)

Sample XML Namespace configurations for each adapter as well as sample code snippets are provided wherever necessary. Of the above libraries, SES and SNS provide outbound adapters only. All other services have inbound and outbound adapters. The SQS inbound adapter is capable of receiving notifications sent out from SNS where the topic is an SQS Queue.

For DymamoDB and SimpleDB, besides providing Inbound- and Outbound Adapters, a MessageStore implementation is provided, too.

Executing the test cases.

All test cases for the adapters are present in the src/test/java folder. On executing the build, maven surefire plugin will execute all the tests.

Please note that all the tests ending with *AWSTests.java connect to the actual Amazon Web Services and are excluded by default in the maven build. All other tests rely on mocking to test the functionality. You need to execute the *AWSTests.java manually to test the connectivity to AWS using your credentials.

All these *AWSTests.java tests look for the file awscredentials.properties in the classpath. To be on the safe side, create the following file at src/test/resources: spring-integration-aws/src/test/resources/awscredentials.properties. It is added to the .gitignore file by default. This will prevent this file to be checked in accidentally and revealing your credentials.

This file needs to have two properties accessKey and secretKey, holding the values of your access key and secret key respectively.

*Note: AWS Services are chargeable and we recommend not to execute the AWSTests.java as part of your regular builds. AWS does provide a free tier which is sufficient to perform your tests without being charged (not true for DynamoDB though), however keep a check on your account usage regularly. Get more information about AWS free tier at http://aws.amazon.com/free/

#Adapters

##Amazon Simple Storage Service (Amazon S3)

###Introduction

###Outbound Channel Adapter ###Inbound Channel Adapter

##Simple Email Service (SES)

There is no adapter for SES, since Spring Cloud AWS provides implementations for org.springframework.mail.MailSender - SimpleEmailServiceMailSender and SimpleEmailServiceJavaMailSender, which can be injected to the <int-mail:outbound-channel-adapter>.

##Amazon Simple Queue Service (SQS)

The SQS adapters are fully based on the Spring Cloud AWS foundation, so for more information about the background components and core configuration, please, refer to the documentation of that project.

###Outbound Channel Adapter

The SQS Outbound Channel Adapter is presented by the SqsMessageHandler implementation (<int-aws:sqs-outbound-channel-adapter>) and allows to send message to the SQS queue with provided AmazonSQS client. An SQS queue can be configured explicitly on the adapter (using org.springframework.integration.expression.ValueExpression) or as a SpEL Expression, which is evaluated against request message as a root object of evaluation context. In addition the queue can be extracted from the message headers under AwsHeaders.QUEUE.

The Java Configuration is pretty simple:

@SpringBootApplication
public static class MyConfiguration {

	@Autowired
	private AmazonSQS amazonSqs;

	@Bean
	public QueueMessagingTemplate queueMessagingTemplate() {
		return new QueueMessagingTemplate(this.amazonSqs);
	}

	@Bean
	@ServiceActivator(inputChannel = "sqsSendChannel")
	public MessageHandler sqsMessageHandler() {
		return new SqsMessageHandler(queueMessagingTemplate());
	}

}

An XML variant may look like:

<aws-messaging:sqs-async-client id="sqs"/>

<int-aws:sqs-outbound-channel-adapter sqs="sqs"
									  channel="sqsSendChannel"
									  queue="foo"/>

###Inbound Channel Adapter

The SQS Inbound Channel Adapter is a message-driven implementation for the MessageProducer and is represented with SqsMessageDrivenChannelAdapter. This channel adapter is based on the org.springframework.cloud.aws.messaging.listener.SimpleMessageListenerContainer to receive messages from the provided queues in async manner and send an enhanced Spring Integration Message to the provided MessageChannel. The enhancements includes AwsHeaders.MESSAGE_ID, AwsHeaders.RECEIPT_HANDLE and AwsHeaders.QUEUE message headers.

The Java Configuration is pretty simple:

@SpringBootApplication
public static class MyConfiguration {

	@Autowired
	private AmazonSQSAsync amazonSqs;

	@Bean
	public PollableChannel inputChannel() {
		return new QueueChannel();
	}

	@Bean
	public MessageProducer sqsMessageDrivenChannelAdapter() {
		SqsMessageDrivenChannelAdapter adapter = new SqsMessageDrivenChannelAdapter(this.amazonSqs, "myQueue");
		adapter.setOutputChannel(inputChannel());
		return adapter;
	}
}

An XML variant may look like:

<aws-messaging:sqs-async-client id="sqs"/>

<int-aws:sqs-message-driven-channel-adapter id="sqsInboundChannel"
                                          sqs="sqs"
										  error-channel="myErrorChannel"
										  queues="foo, bar"
										  delete-message-on-exception="false"
										  max-number-of-messages="5"
										  visibility-timeout="200"
										  wait-time-out="40"
										  send-timeout="2000"/>

The SqsMessageDrivenChannelAdapter exposes all SimpleMessageListenerContainer attributes to configure and one an important of them is deleteMessageOnException, which is true by default. Having that to false, it is a responsibility of end-application to delete message or not on exceptions. E.g. in the error flow on the error-channel of this channel adapter. For this purpose a AwsHeaders.RECEIPT_HANDLE message header must be used for the message deletion:

MessageHeaders headers = message.getHeaders();
this.amazonSqs.deleteMessageAsync(
          new DeleteMessageRequest(headers.get(AwsHeaders.QUEUE), headers.get(AwsHeaders.RECEIPT_HANDLE)));

##Amazon Simple Notification Service (SNS)

Amazon SNS is a publish-subscribe messaging system that allows clients to publish notification to a particular topic. Other interested clients may subscribe using different protocols like HTTP/HTTPS, e-mail or an Amazon SQS queue to receive the messages. Plus mobile devices can be registered as subscribers from the AWS Management Console.

Unfortunately Spring Cloud AWS doesn't provide flexible components which can be used from the channel adapter implementations, but Amazon SNS API is pretty simple, from other side. Hence Spring Integration AWS SNS Support is straightforward and just allows to provide channel adapter foundation for Spring Integration applications.

Since e-mail, SMS and mobile devices subscription/unsubscription confirmation is out of the Spring Integration application scope and can be done only from the AWS Management Console, we provide only HTTP/HTTPS SNS endpoint in face of SnsInboundChannelAdapter. The SQS-to-SNS subscription can be done with the simple usage of com.amazonaws.services.sns.util.Topics#subscribeQueue(), which confirms subscription automatically.

###Inbound Channel Adapter

The SnsInboundChannelAdapter (<int-aws:sns-inbound-channel-adapter>) is an extension of HttpRequestHandlingMessagingGateway and must be as a part of Spring MVC application. Its URL must be used from the AWS Management Console to add this endpoint as a subscriber to the SNS Topic. However before receiving any notification itself this HTTP endpoint must confirm the subscription.

See SnsInboundChannelAdapter JavaDocs for more information.

An important option of this adapter to consider is handleNotificationStatus. This boolean flag indicates if the adapter should send SubscriptionConfirmation/UnsubscribeConfirmation message to the output-channel or not. If that the AwsHeaders.NOTIFICATION_STATUS message header is present in the message with the NotificationStatus object, which can be used in the downstream flow to confirm subscription or not. Or "re-confirm" it in case of UnsubscribeConfirmation message.

In addition the AwsHeaders#SNS_MESSAGE_TYPE message header is represent to simplify a routing in the downstream flow.

The Java Configuration is pretty simple:

@SpringBootApplication
public static class MyConfiguration {

	@Autowired
	private AmazonSNS amazonSns;

	@Bean
    public PollableChannel inputChannel() {
    	return new QueueChannel();
    }

    @Bean
    public HttpRequestHandler sqsMessageDrivenChannelAdapter() {
    	SnsInboundChannelAdapter adapter = new SnsInboundChannelAdapter(amazonSns(), "/mySampleTopic");
    	adapter.setRequestChannel(inputChannel());
    	adapter.setHandleNotificationStatus(true);
    	return adapter;
    }
}

An XML variant may look like:

<int-aws:sns-inbound-channel-adapter sns="amazonSns"
										 path="/foo"
										 channel="snsChannel"
										 error-channel="errorChannel"
										 handle-notification-status="true"
										 payload-expression="payload.Message"/>
```

Note: by default the message `payload` is a `Map` converted from the received Topic JSON message. For the convenient
the `payload-expression` is provided with the `Message` as a root object of the evaluation context. Hence even some
HTTP headers, populated by the `DefaultHttpHeaderMapper`, are available for the evaluation context.

###Outbound Channel Adapter

The `SnsMessageHandler` (`<int-aws:sns-outbound-channel-adapter>`) is a simple one-way Outbound Channel Adapter
to send Topic Notification using `AmasonSNS` service.

This Channel Adapter (`MessageHandler`) accepts these options:

- `topic-arn` (`topic-arn-expression`) - the SNS Topic to send notification for. The `ResourceIdResolver` can be used
from the SpEL definition to determine the target Topic Arn from the local logical name;
- `subject` (`subject-expression`) - the SNS Notification Subject;
- `body-expression` - the SpEL expression to evaluate the `message` property for the
`com.amazonaws.services.sns.model.PublishRequest`.

See `SnsMessageHandler` JavaDocs for more information.

The Java Config looks like:

````java
@Bean
public MessageHandler snsMessageHandler() {
    SnsMessageHandler handler = new SnsMessageHandler(amazonSns());
    adapter.setTopicArn("arn:aws:sns:eu-west:123456789012:test);
    String bodyExpression = "SnsBodyBuilder.withDefault(payload).forProtocols(payload.substring(0, 140), 'sms')";
    handler.setBodyExpression(spelExpressionParser.parseExpression(bodyExpression));
    return handler;
}

NOTE: the bodyExpression can be evaluated to a org.springframework.integration.aws.support.SnsBodyBuilder allowing the configuration of a json messageStructure for the PublishRequest and provide separate messages for different protocols. The same SnsBodyBuilder rule is applied for the raw payload if the bodyExpression hasn't been configured. NOTE: if the payload of requestMessage is a com.amazonaws.services.sns.model.PublishRequest already, the SnsMessageHandler doesn't do anything with it and it is sent as-is.

The XML variant may look like:

<int-aws:sns-outbound-channel-adapter
			id="snsAdapter"
			sns="amazonSns"
			channel="notificationChannel"
			topic-arn="foo"
			subject="bar"
			body-expression="payload.toUpperCase()"/>

###Outbound Gateway

The <int-aws:sns-outbound-gateway> is fully similar to the one-way channel adapter. The only difference that in gateway mode the SnsMessageHandler produces the reply Message as:

return getMessageBuilderFactory()
           .withPayload(publishRequest)
           .setHeader(AwsHeaders.TOPIC, publishRequest.getTopicArn())
           .setHeader(AwsHeaders.SNS_PUBLISHED_MESSAGE_ID, publishResult.getMessageId());

The reply from the <int-aws:sns-outbound-gateway> may be useful to track and correlate the SNS message in the downstream flow.

With Java configuration there is just enough to use constructor of SnsMessageHandler with produceReply boolean flag to true ot switch it to the gateway mode. By default the SnsMessageHandler is one-way MessageHandler.