README

lambda-logger

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.

Usage

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:

Use import/export syntax locally and ensure your local tooling uses the ESM build, e.g. by using the esm module.
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
            '@financial-times/lambda-logger':
                '@financial-times/lambda-logger/dist/lambda-logger.js',
        },
    },
};

API

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
- AWS_EXECUTION_ENV,
- AWS_LAMBDA_FUNCTION_NAME,
- AWS_LAMBDA_FUNCTION_MEMORY_SIZE,
- AWS_LAMBDA_FUNCTION_VERSION
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.

Configuration

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.

Usage no npm install needed!