Structured Logging

Structured Logging Overview

At its core, structured logging is about doing one thing well inside your AWS Lambda project. Once you understand the pattern, you can apply it consistently across features and teams.

Good structured logging pays off across the whole codebase: fewer surprises, easier testing, and smoother onboarding. The snippet below is a solid starting point.

export const handler = async (event) => {
  console.log(JSON.stringify({
    level: 'info',
    requestId: event.requestContext?.requestId,
    message: 'order received',
  }));

  return { ok: true };
};

Structured JSON logs are searchable in CloudWatch Logs Insights and pair well with X-Ray traces.

Structured Logging Example

// handler.mjs
export const handler = async (event, context) => {
  // 1. read input from the event
  // 2. do the work
  // 3. return a response (or throw on error)
};

• Start from a minimal Structured Logging example and grow it only as needed.
• Keep configuration explicit so Structured Logging behaves the same in every environment.
• Name things clearly so teammates understand your Structured Logging at a glance.
• Add tests around Structured Logging early to lock in expected behaviour.

AWS Lambda Cheatsheet

Handy reference for working with structured logging in AWS Lambda and Node.js.

How Structured Logging Works in AWS Lambda

Structured Logging runs inside the managed Lambda execution environment. AWS provisions a micro-VM, loads your Node.js code, runs any module-scope initialisation once, and then invokes your handler for each event.

Structured JSON logs are searchable in CloudWatch Logs Insights and pair well with X-Ray traces.

• Handlers should be small and do one job well.
• Initialise SDK clients and config outside the handler to reuse them on warm starts.
• Return quickly and let event sources handle retries where possible.
• Emit structured logs so CloudWatch and X-Ray can correlate activity.

Practical Guidance for Structured Logging

On real projects, structured logging works best when it is observable, secure, and cheap to run. Grant least-privilege IAM, validate every input, and keep the deployment package small.

Common Mistakes

• Copying structured logging snippets without understanding what each line does.
• Skipping error handling and edge cases when wiring up structured logging.
• Leaving structured logging untested, so regressions slip into production.
• Over-engineering structured logging before you actually need the extra flexibility.

Key Takeaways

• Structured Logging is a core part of working effectively with AWS Lambda.
• Start small and keep structured logging focused on a single responsibility.
• Apply consistent patterns so structured logging scales across your project.
• Test and document structured logging to keep it maintainable over time.