Logger used by the lambda team. Logs in JSON format using pino

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1504.0.03 months ago5 years agoMinified + gzip package size for @financial-times/lambda-logger in KB


Logger useful for AWS lambda applications, particularly those which are aggregated in Splunk. Logs in JSON format using pino.
This was created to provide a simple logger, compatible with lambda, which outputs in a JSON format (n-logger) was previously used but didn't handle nested JSON fields or provide a JSON option).
This does make process.stdout.write a blocking function (process.stdout._handle.setBlocking(true);), as AWS Lambda previously streamed to an output which was synchronous, but has since changed to asynchronous behaviour, leading to lost logs.
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const logger = require('@financial-times/lambda-logger');

logger.info({ importantField: 'some-field' }, 'Logging a thing');

Build exports

This module exports both
  • a commonjs build (the main field in package.json)
  • an ESM (ecmascript module) build (the module field in package.json)

If you're using commonjs and webpack, say with serverless-webpack it will try to load the ESM build out of the box. This exports a default export, and as such won't work if using commonjs.
The solutions to this problem are:
  1. Use import/export syntax locally and ensure your local tooling uses the ESM build, e.g. by using the esm module.
  2. Setup a webpack alias to the commonjs build:

// webpack.config.js

module.exports = {
	resolve: {
		alias: {
			// use commonjs export of lambda-logger to avoid having to use import/export syntax locally


The logger's API is identical to that of pino with the following exceptions:
  • The property sourcetype: _json is added to logs in production for Splunk compatibility.
  • Lambda related environment variables are added by default:
  • Defaults to ISO timestamp logging for splunk compatiblity. At the time of writing this incurs a 25% pino performance penalty.

Pino properties

Pino adds the following properties to logs by default:
  • level - the log level in string form. This is translated from the pino default of logging an integer representation.
  • v - the pino logger API version.
  • hostname - the hostname the process is running on.
  • pid - the process PID.


  • NODE_ENV - pretty printing is enabled when NODE_ENV !== 'production'.
  • CONSOLE_LOG_LEVEL - determines the level to log at (pinto level option). Defaults to info.
  • SYSTEM_CODE - adds the systemCode property to every log.
  • ENVIRONMENT|STAGE - adds the environment property to every log. STAGE is used as a fallback due to it's default definition in the serverless framework.