Building Scalable Event-Driven Orchestration Platform in AWS

These days, we’re surrounded by apps everywhere—on our phones, in our smart homes, and throughout businesses big and small. It’s almost unbelievable how much data they churn out every single day. We're talking billions or trillions of events, from a simple tap on a phone screen to complex business transactions. It is essential for applications to handle these events in real-time to act on them as they occur and derive useful insights for the growth of the business.

\ Now, imagine if we could tap into all this information as it happens, in real-time. That's where the magic of event-driven architecture comes in. It's like having a super-efficient personal assistant for the application, one that is always on the job and can handle a huge number of tasks.

Sample Applications of Event-Driven Architecture

• E-Commerce Platforms

  Each time an order is placed, it triggers events that are received by multiple services. As the order is confirmed, an event is sent to update inventory, process the payment, order tracking, and send email confirmation. All of these happen instantly and independently from each other.

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• Online Multiplayer Gaming Platforms

  Every player's action whether it’s scoring points or making a move creates events that update the game state, update game sources, and keep everyone in the game on the same page.

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• Social Media Platforms

  Every action by the user for example liking a post, or following another person or group impacts triggers events. Messages, comments, and other interactions trigger their own events, allowing real-time updates across millions or billions of users.

  \ Many other real-world scenarios are suitable as a perfect match for event-driven architecture.

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Event-Driven Orchestration in AWS

Handling such a massive flow of events requires an event orchestration platform that is highly scalable, resilient, and reliable. The platform should scale as the events grow, should handle spikes on the load of events, and deliver the events to each relevant service without fail.

\ AWS provides SNS (Simple Notification Service), SQS (Simple Queue Service), and Lambda to build such an orchestration platform with ease. We can build a sophisticated orchestration platform with these key elements in AWS.

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• SNS acts as a message publisher, notifying all subscribers when an event occurs. It allows for a fan-out model where multiple endpoints (e.g., SQS queues, Lambda functions) can receive the same message simultaneously.
• SQS can subscribe to SNS and it acts as a durable message queue, buffering requests, and decoupling services. SQS ensures reliable message delivery and provides visibility and dead-letter queues to handle failed messages.
• Lambda handles event processing logic. Each Lambda function is stateless, scaling automatically based on incoming events. It can consume events from SQS queues, process data, and invoke other services as necessary.

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\ \ Note that SNS can deliver events directly to the application service without SQS/Lambda in the flow. There are many advantages of using SQS & Lambda, few of them are:

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• Reliability

  SQS gives us the ability to buffer the events if the service is temporarily unavailable or under heavy load

• Event Filtering

  We can choose which events that SQS can subscribe to

• Error Handling

  By combining SQS + Lambda, we gain enhanced error-handling capability and retry mechanisms

Example Orchestration Flow

• Event Trigger

  A user places an order. This triggers an SNS notification to distribute the event to multiple interested services

• Fan-Out

  SNS sends the message to various SQS queues (based on the filtering of events). Each queue can belong to a corresponding service - Inventory Service, Payment Processor Service, or Notification Service

• Processing

  Each SQS queue triggers its respective Lambda function, which sends the event to the corresponding service

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Monitoring and Alerting

Ensuring high availability and reliability for your event-driven applications requires thorough monitoring and alerting

• AWS CloudWatch: Monitors Lambda invocations, SQS queue depth, and SNS message delivery. We can set up CloudWatch Alarms to alert on metrics like
• Lambda duration, errors, and throttling
• SQS queue message delay and age
• SNS delivery success rates
• AWS X-Ray: Allows tracing of Lambda invocations and helps pinpoint latencies or issues in inter-service communications
• AWS CloudTrail: Logs all SNS, SQS, and Lambda actions, providing an audit trail for actions and configurations within your application

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SLA & Scaling

Understanding SLAs for each AWS service in the stack ensures the architecture meets uptime and availability requirements.

| Service | SLA | Scale & Key Limitations | |----|----|----| | SNS | 99.9% | Scales automatically; high publish rate of up to tens of millions of messages per second. | | SQS | 99.9% | Allows up to 3000 messages per second per queue; messages retained for up to 14 days. | | Lambda | 99.95% | Automatically scales in response to events; 1000 concurrent executions per account by default (can be increased). |

These SLAs help ensure that your services remain available and resilient to handle high-traffic periods, with each component designed to meet varying throughput and reliability needs.

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Building the Application Step-By-Step

The Cloudformation templates for orchestration platform is available here. We can go through the important snippets of the templates in the following sections.

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• Create SNS Topic

  Define an SNS topic. SNS will handle the fan-out to subscribed queues.

EventTopic: Type: AWS::SNS::Topic Properties: DisplayName: !Ref EventsTopicName TopicName: !Ref EventsTopicName FifoTopic: true ContentBasedDeduplication: true KmsMasterKeyId: "alias/aws/sns" Tags: - Key: "Tag1" Value: "Value1"

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• Setup SQS Queue

  For each downstream service, create an SQS queue

EventsSQSQueue: Type: AWS::SQS::Queue Properties: FifoQueue: true DeduplicationScope: messageGroup FifoThroughputLimit: perMessageGroupId ContentBasedDeduplication: true QueueName: !Ref EventsSQSName SqsManagedSseEnabled: true VisibilityTimeout: 120 Tags: - Key: "Tag1" Value: "Value1"

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• Setup Lambda Functions

  Create Lambda functions that will process messages from each SQS queue.

EventsLambda: Type: AWS::Lambda::Function Properties: FunctionName: !Ref LambdaFunctionName Description: Handle SQS Events for Orchestration Platform Handler: index.lambda_handler Runtime: python3.12 Timeout: 120 Role: !GetAtt EventsLambdaRole.Arn Tags: - Key: "Tag1" Value: "Value1" Code: ZipFile: | def lambda_handler(event, context): print(F"Hurray! I got an event: {event}")

\ \ The rest of the templates to create subscriptions, roles, are available in Github Repo. Use CloudWatch metrics and alarms to track message failures, Lambda duration, errors, and other key metrics.

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Scaling Considerations

This event-driven platform automatically scales:

• SNS offers high scalability with an inherent upper limit on subscribers or messages.
• SQS supports robust scalability, with very high message throughput per queue.
• Lambda provides automatic scaling that adjusts concurrency based on incoming request rates.

Conclusion

AWS’s event-driven orchestration platform with SNS, SQS, and Lambda allows for a powerful, and flexible approach to build scalable and resilient applications. From e-commerce order processing to data pipelines, this serverless approach enables developers to build powerful, decoupled applications capable of handling complex workflows across multiple services. To ensure observability and maintainability, AWS provides integrated monitoring and debugging tools.