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    4.0.0 • Public • Published


    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');{ 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:
      • AWS_REGION
    • 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.




    npm i @financial-times/lambda-logger

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