Introduction to AWS Lambda Logger

AWS Lambda is a powerful tool for running code without provisioning or managing servers. Effective logging is crucial for monitoring, debugging, and maintaining Lambda functions. The aws-lambda-logger library provides a comprehensive API for logging within AWS Lambda functions, ensuring you can capture, analyze, and act upon logs efficiently. In this guide, we will explore various aws-lambda-logger APIs with examples to help you make the most of this library.

Basic Logging

Start by importing the logger and creating a basic log entry:

  
  const logger = require('aws-lambda-logger');

  exports.handler = async (event) => {
    logger.log('info', 'This is an informative log entry');
    return { statusCode: 200, body: 'Hello, world!' };
  };
  

Logging Different Levels

aws-lambda-logger allows you to log messages at different levels: debug, info, warn, and error:

  
  logger.debug('This is a debug message');
  logger.info('This is an informational message');
  logger.warn('This is a warning message');
  logger.error('This is an error message');
  

Structured Logging with JSON

Structured logging can be more useful for debugging by including additional context:

  
  logger.info('User login', {
    userId: '12345',
    ipAddress: '192.168.1.1'
  });
  

Setting Log Level at Runtime

You can set the log level dynamically, which is useful for different environments (e.g., development or production):

  
  logger.setLogLevel('debug');
  logger.debug('This will be logged');
  logger.setLogLevel('warn');
  logger.debug('This will NOT be logged');
  

Logging Errors with Stack Traces

When logging errors, include stack traces for more detailed debugging:

  
  try {
    throw new Error('Something went wrong');
  } catch (error) {
    logger.error('An error occurred', { error: error.stack });
  }
  

Async Logging

Ensure that all logs are captured in asynchronous handlers:

  
  exports.handler = async (event) => {
    await logger.log('info', 'Handling event asynchronously');
    return { statusCode: 200, body: 'Event processed' };
  };
  

App Example

Here is an example of an AWS Lambda function that uses multiple APIs from aws-lambda-logger:

  
  const logger = require('aws-lambda-logger');

  exports.handler = async (event) => {
    logger.info('Processing event', event);

    try {
      // Simulate an action
      if (event.action === 'fail') {
        throw new Error('Simulated failure');
      }
      logger.info('Action succeeded', { action: event.action });
      return { statusCode: 200, body: 'Success' };
    } catch (error) {
      logger.error('Action failed', { action: event.action, error: error.stack });
      return { statusCode: 500, body: 'Internal Server Error' };
    }
  };
  

By following this guide, you can effectively manage logs within your AWS Lambda functions using aws-lambda-logger, improving your ability to monitor, debug, and analyze your serverless applications.

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