Serverless AWS Lambda Development · レッスン

エラーハンドリングとリトライ

堅牢なエラーハンドリングの仕組みと自動リトライを実装し、呼び出しエラーを理解して、より回復力の高いサーバーレスシステムを構築します。

「エラーハンドリングとリトライ」はCoddyKit上の無料Serverless AWS Lambda Developmentレッスンです。これはレッスン2/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはServerless AWS Lambda Development学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Serverless AWS Lambda Developmentコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Why Error Handling Matters

In serverless applications, things can go wrong. Your function might fail, a dependency might be unavailable, or an event might be malformed.

Robust error handling is crucial for building resilient systems that can recover gracefully and notify you when issues occur. This lesson explores how AWS Lambda helps you achieve this.

Types of Lambda Errors

When working with Lambda, it's helpful to understand different types of errors:

Invocation Errors: Problems occurring before your code runs, like incorrect IAM permissions for Lambda to read from an event source.
Function Errors: Exceptions thrown by your function code, timeouts, or out-of-memory errors. These are the errors you primarily handle within your code.
Service Errors: Rare issues with the underlying AWS Lambda service itself.

Sync vs. Async Error Paths

How Lambda handles errors depends on the invocation type:

Synchronous: (e.g., via API Gateway, ALB) Lambda returns the error directly to the caller. The caller is responsible for retries.
Asynchronous: (e.g., via S3, SNS, SQS) Lambda places the event in an internal queue and automatically retries the function if it fails. You don't get immediate feedback.

We'll focus mostly on asynchronous error handling and retries in this lesson.

Lambda's Async Retries

For asynchronous invocations, Lambda automatically retries your function if it fails due to an unhandled exception or times out.

By default, Lambda retries twice (total of 3 attempts).
These retries are automatic and happen with a delay, often with exponential backoff.
This built-in mechanism helps ensure temporary issues don't lead to lost events.

Configuring Async Retries

You can customize the asynchronous invocation settings for your Lambda function:

Maximum retry attempts: Set this from 0 to 2. Setting it to 0 means no retries.
Maximum event age: Define how long Lambda should keep an event in its queue for retries, from 60 seconds to 6 hours.

These settings give you control over how long and how often Lambda attempts to process a failed event.

Catching Failed Events with DLQs

Even with retries, some events might still fail consistently (e.g., due to malformed data). These are often called 'poison pill' messages.

A Dead Letter Queue (DLQ) is a designated destination (an SQS queue or SNS topic) where Lambda sends events that have exhausted all retry attempts.

DLQs are vital for debugging, preventing data loss, and analyzing why certain events couldn't be processed.

Setting Up Your DLQ

To use a DLQ:

Create an Amazon SQS queue or SNS topic.
Configure your Lambda function's asynchronous invocation settings to point to this SQS queue or SNS topic as its DLQ.
Ensure your Lambda function's execution role has permissions to send messages to the chosen DLQ (e.g., sqs:SendMessage or sns:Publish).

This ensures that no event is truly 'lost' even after multiple failures.

Handling Errors in Your Code

While Lambda handles retries, you should still implement error handling within your function code using try-catch blocks. This allows you to:

Gracefully manage expected errors.
Log detailed context for debugging.
Perform cleanup or partial rollbacks before re-throwing an exception to trigger Lambda's retry mechanism.

Try running this simple Java example:

public class Main {
  public static void main(String[] args) {
    processData("valid data");
    System.out.println("------------------");
    processData("data with error");
  }

  public static void processData(String data) {
    try {
      System.out.println("Attempting to process: " + data);
      if (data.contains("error")) {
        throw new RuntimeException("Critical processing error!");
      }
      System.out.println("Successfully processed: " + data.toUpperCase());
    } catch (Exception e) {
      System.err.println("Caught an error: " + e.getMessage());
      System.err.println("Further action (e.g., logging, retry logic) would go here.");
      // In a real Lambda, re-throwing would trigger a retry for async invocations
    }
  }
}

Understanding Invocation Errors

Sometimes, Lambda can't even start your function. These are invocation errors.

Examples: Incorrect IAM permissions for Lambda to access an S3 bucket trigger, a misconfigured VPC, or exceeding service quotas before execution.
Detection: These errors often appear in CloudWatch Logs for your function or as `Invocation errors` metrics in the Lambda console. They are not typically handled by your function's try-catch blocks.

Quick Check on Retries

Let's test your understanding of error handling and retries in AWS Lambda.

Recap: Building Resilient Lambdas

You've learned how to make your serverless applications more robust:

Differentiated between various types of Lambda errors.
Understood how synchronous vs. asynchronous invocations handle errors differently.
Explored Lambda's automatic retry mechanism for asynchronous calls.
Discovered the importance of Dead Letter Queues (DLQs) for failed events.
Saw how to implement basic error handling within your code using try-catch.

By applying these techniques, you can build more resilient and reliable serverless systems.

よくある質問

「エラーハンドリングとリトライ」レッスンは無料ですか？

はい。「エラーハンドリングとリトライ」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Serverless AWS Lambda Developmentコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Serverless AWS Lambda Developmentコースには全4レッスンが含まれています。

「エラーハンドリングとリトライ」で何を学びますか？

堅牢なエラーハンドリングの仕組みと自動リトライを実装し、呼び出しエラーを理解して、より回復力の高いサーバーレスシステムを構築します。ブラウザで直接実行するハンズオンコードでServerless AWS Lambda Developmentを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

Serverless AWS Lambda Developmentを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのServerless AWS Lambda Developmentは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン2/4です。

「エラーハンドリングとリトライ」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このServerless AWS Lambda Developmentレッスンでコードを書いて実行できますか？

はい。すべてのServerless AWS Lambda Developmentレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

このコースのすべてのレッスン

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