Error Handling & Retries in AWS Serverless

1. Introduction

In serverless architectures, particularly when using AWS Lambda, understanding error handling and retries is crucial for building resilient applications. This lesson covers essential concepts, strategies for handling errors, and methods for implementing retries effectively.

2. Key Concepts

• Idempotency: Ensuring that repeated execution of the same operation results in the same effect.
• Asynchronous Processing: Lambda functions can be invoked in an asynchronous manner, affecting how errors are managed.
• Dead Letter Queues (DLQ): A secondary queue for capturing failed events for later analysis.

3. Error Handling

Error handling in AWS Lambda can be categorized into synchronous and asynchronous invocations. Different strategies apply based on the invocation type.

3.1 Synchronous Error Handling

For synchronous invocations (e.g., API Gateway), errors can be captured and managed within the Lambda function. Use try-catch blocks to handle exceptions:

        exports.handler = async (event) => {
            try {
                // Your code logic
                throw new Error("An example error");
            } catch (error) {
                console.error("Error:", error);
                throw error; // Propagate error
            }
        };
        

3.2 Asynchronous Error Handling

For asynchronous invocations, AWS Lambda automatically retries the execution of failed invocations twice. You can configure a Dead Letter Queue (DLQ) to capture these failed events.

4. Retries

AWS Lambda automatically retries failed asynchronous invocations. However, you can implement custom retry logic using libraries or frameworks.

4.1 Manual Retry Logic

Implementing a manual retry mechanism can be useful. Here’s a simple example of retries using a loop:

        const MAX_RETRIES = 3;

        exports.handler = async (event) => {
            let attempt = 0;
            while (attempt < MAX_RETRIES) {
                try {
                    // Your code logic here
                    return "Success!";
                } catch (error) {
                    attempt++;
                    console.error(`Attempt ${attempt} failed:`, error);
                    if (attempt === MAX_RETRIES) throw error; // Final failure
                }
            }
        };
        

5. Best Practices

• Use try-catch blocks to effectively manage errors.
• Implement idempotency to handle retries safely.
• Configure Dead Letter Queues to capture failed events.
• Utilize exponential backoff strategies for custom retries.
• Monitor and log errors for ongoing analysis and improvement.

6. FAQ