Monitoring and Tracing in Event-Driven Architectures: A Guide to AWS X-Ray
Tags: aws, serverless, architecture, devops
Published: 2022-12-20 19:48:33

[**Event-driven architecture**](https://blog.guilleojeda.com/event-driven-architectures-in-aws-building-scalable-and-responsive-applications) is a powerful design pattern that places events as the central component of the system. When events are generated by external sources, they trigger a sequence of actions within the system. In this architecture, the components don't invoke other components directly, but they emit events with no knowledge of what other components might be subscribed to those events. This reduces coupling between components, allowing them to scale independently. However, managing an event-driven architecture can be quite challenging due to its inherent complexity and distributed nature. Fortunately, [**AWS X-Ray can help with tracing and monitoring**](https://newsletter.simpleaws.dev/p/using-aws-xray-observability-eventdriven-architectures).

## Challenges in Event-Driven Architectures

Managing an event-driven architecture requires proper tracing and monitoring, which can be challenging due to its distributed nature. With no adequate tracing mechanisms in place, identifying the root cause of an issue becomes especially difficult. Monitoring an event-driven architecture is another problem altogether. Individual components can be monitored just fine, but a holistic view of the system is much harder to achieve.

Monitoring means collecting data and metrics about the system, so you can better understand its performance. This can include things like:

* Tracking the number of events processed per second
    
* Monitoring the response time of the system
    
* Monitoring the overall health of the system
    

Tracing is the process of tracking a specific request or event as it travels through the system. This helps you understand how the system is processing a particular event, and identify bottlenecks and other issues.

## **What is AWS X-Ray**

AWS X-Ray is a service that enables you to monitor and trace applications and microservices, including serverless applications. It provides detailed visibility into the request and event flow of the system, giving you the tools you need to troubleshoot issues in event-driven architectures.

With AWS X-Ray you can trace requests and events as they travel through the system, view performance metrics in real-time, and generate reports. This is especially useful for event-driven architectures, where understanding how requests travel through the system is particularly difficult.

## **Benefits of using AWS X-Ray**

Using AWS X-Ray in event-driven architectures has several benefits:

1. **Improved troubleshooting**: AWS X-Ray provides detailed traces and visualizations of the request flow, which helps you quickly identify and resolve issues.
    
2. **Enhanced performance**: By identifying bottlenecks and other performance issues, you can optimize your architecture for better performance.
    
3. **Greater visibility**: AWS X-Ray provides a holistic view of your system, making it easier to understand how individual components interact with one another.
    
4. **Easier collaboration**: AWS X-Ray's detailed traces and visualizations can be shared among team members, making it easier for everyone to understand the system and collaborate on resolving issues.
    

## **How To Use AWS X-Ray in Event-driven Architectures**

Let's consider an example event-driven architecture built on AWS using Node.js: An order-processing system. When a user places an order, it triggers an event that is picked up by an AWS Lambda function. This function then writes the order to a DynamoDB table and sends a message to an SNS topic. The SNS topic triggers another Lambda function, which sends a confirmation email to the user.

Let's consider a typical problem with this architecture. Most orders are processed successfully, but sometimes a user doesn't receive the confirmation email. Without proper monitoring and tracing, it can be very difficult to identify the root cause of this problem. That's what AWS X-Ray solves.

AWS X-Ray is so important in these scenarios that it's been included in [a list of 20 Advanced Tips for Lambda](https://newsletter.simpleaws.dev/p/simple-aws-20-advanced-tips-lambda).
    

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---

## **How to set up AWS X-Ray**

Setting up AWS X-Ray is easy and straightforward. First, set up AWS X-Ray in your order-processing Lambda function by installing the AWS X-Ray SDK for Node.js. Then, wrap the code in an X-Ray segment. If you're using the AWS SDK or HTTP requests, you need to wrap them with the captureAWS and captureHTTPsGlobal functions, respectively. After you've added AWS X-Ray to your Node.js functions, you need to modify your DynamoDB table and SNS topic to be X-Ray enabled. Let's see it in more detail.

### **How to set up AWS X-Ray in a Lambda function using Node.js**

Install the AWS X-Ray SDK for Node.js:

```javascript
npm install aws-xray-sdk
```

Require the AWS X-Ray SDK at the top of your Lambda function code:

```javascript
const AWSXRay = require('aws-xray-sdk');
```

Wrap the code in an X-Ray Segment:

```javascript
const segment = new AWSXRay.Segment('my-function-name');

AWSXRay.captureAsyncFunc('my-function-name', function(callback) {
  // Your code
  callback();
});
```

If you're using the AWS SDK (for example to write to our DynamoDB table), you need to wrap it with the captureAWS function:

```javascript
const AWS = AWSXRay.captureAWS(require('aws-sdk'));
```

If you are using HTTP requests, you can wrap the https package with the captureHTTPsGlobal function:

```javascript
AWSXRay.captureHTTPsGlobal(require('https'));
```

This is a complete example of a Lambda function that has been modified to use the AWS X-Ray SDK:

```javascript
const AWSXRay = require('aws-xray-sdk');
const AWS = AWSXRay.captureAWS(require('aws-sdk'));
AWSXRay.captureHTTPsGlobal(require('https'));

exports.handler = async (event) => {
  const segment = new AWSXRay.Segment('my-function-name');

  try {
    // Your code goes here
  } catch (error) {
    console.error(error);
    throw error;
  } finally {
    segment.close();
  }
};
```

Remember to add AWS X-Ray to both your order-processing Lambda function and your email sending Lambda function.

### How to set up AWS X-Ray for DynamoDB

To set up AWS X-Ray for DynamoDB, follow these simple steps:

1. In the list of tables, click on the name of the table.
    
2. On the Table Details page, click the "Actions" dropdown and select "Modify".
    
3. In the "Advanced settings" section, click the "Edit" button that's next to the "AWS X-Ray tracing" setting.
    
4. In the "AWS X-Ray Tracing" dialog, select "Yes".
    
5. Click "Save".
    

### How to set up AWS X-Ray for SNS

To set up AWS X-Ray for SNS, follow these simple steps:

1. In the list of topics, click on the name of the SNS Topic.
    
2. On the topic details page, click the "Actions" dropdown and select "Modify".
    
3. In the "Advanced settings" section, click the "Edit" button next to the "AWS X-Ray tracing" setting.
    
4. In the "AWS X-Ray Tracing" dialog, select "Yes".
    
5. Click "Save".
    

## Using AWS X-Ray to Trace and Debug Applications

Once AWS X-Ray is set up in every component, we can use it to solve the problem of some users not receiving the confirmation email.

The X-Ray console can show a trace of a request that is experiencing problems and display exactly where the request is getting stuck. We might find that the message sent to the SNS topic is not reaching its intended destination. Or perhaps the second Lambda function is encountering an error when trying to send the confirmation email.

Once we know where the problem is, we can set out to fix it. We can modify the Lambda function to retry the request if it fails, or add additional error handling logic for uncaught errors.

## Best Practices for AWS X-Ray

To get the most out of AWS X-Ray, follow these tips and best practices:

* Enable X-Ray for all relevant components: To get the most out of X-Ray, it's important to enable it for all relevant components of your system. This includes Lambda functions, DynamoDB tables, and SNS topics.
    
* Use the X-Ray console and API to view and analyze trace data: Use the console to view a visual representation of your trace data. Use the API to programmatically access and manipulate trace data, and automate tasks such as performance analysis or error reporting.
    
* Use segments and subsegments to add context to your trace data: Use segments to represent the overall flow of a request through the system. Use subsegments to represent specific actions within that flow. By adding context to your trace data, you can more easily understand and troubleshoot issues that may be occurring.
    
* Enable sampling to reduce the overhead of tracing: Tracing can add overhead to your system, particularly if you are instrumenting a large number of functions or if your functions are being invoked frequently. To reduce this overhead, you can enable sampling in X-Ray. This will cause X-Ray to only trace a subset of requests, which can significantly reduce the overhead of tracing, as well as the costs.
    
* Use custom attributes to add context to your trace data: Custom attributes are key-value pairs that you can add to your trace data to provide additional context. Use custom attributes to add metadata about your requests, such as user IDs or request IDs.
    
* Use the X-Ray SDK to add error handling to your Lambda functions: The X-Ray SDK provides a `captureFunc` method that you can use to capture errors and add them to trace data.
    

## Conclusion

Monitoring and tracing are critical in event-driven architectures. AWS X-Ray provides detailed visibility into the request and event flow of the system, giving you the tools you need to troubleshoot issues in event-driven architectures. By following the steps outlined in this article, you can easily set up AWS X-Ray for your event-driven architecture and enjoy the benefits of better tracing and monitoring.

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