A nodejs logger for AWS Lambda

• Writes logs to stdout using console.log
• Logs in JSON format
• Supports log levels: DEBUG, INFO, WARN, ERROR and OFF
• Defaults to log level INFO
• Support for pretty print when debugging
• Built using typescript and includes types

Basic example:

import { APIGatewayEvent } from 'aws-lambda';
import { log } from 'pn-lambda-logger';
import { ok } from '../aws/response';

export const healthCheck = async (event: APIGatewayEvent, context: AWSLambda.Context, cb: AWSLambda.Callback) => {

// A standard INFO log message
log.info('My message');

}

  // Output
  {
    "@timestamp": 1541421856289,
    "level": "INFO",
    "message": "My message"
  }

Context and meta data

import { APIGatewayEvent } from 'aws-lambda';
import { log } from 'pn-lambda-logger';
import { ok } from '../aws/response';

export const healthCheck = async (event: APIGatewayEvent, context: AWSLambda.Context, cb: AWSLambda.Callback) => {

  // Setup so that the AWS Lambda meta data will be added to log output
  log.setup({ context, host: event.headers['Host'], verb: event.httpMethod, useragent: event.headers['User-Agent'], query: event.queryStringParameters, path: event.path, xRequestId: event.headers['X-Request-ID'] });

  // A standard INFO log message
  log.info({ message: 'Message' });

  cb(null, ok({ status: 'UP' }));
};

{
  "@timestamp": 1541460988579,
  "level": "INFO",
  "message": "Message",
  "host": "abc123.execute-api.eu-west-1.amazonaws.com",
  "verb": "GET",
  "path": "/manage/health",
  "useragent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.77 Safari/537.36",
  "query": {
    "hello": "world"
  },
  "awsRequestId": "asdas-adsas-asdasdas-asdasda-adss",
  "functionName": "hello",
  "invokedFunctionArn": "arn:cccccc",
  "memoryLimitInMB": 1024,
  "remainingTime": 11147
}

Log Levels

The default log level is INFO log.level = LogLevels.INFO;. To show debug messages you need to explicitly set the log.level to DEBUG like this:

// Set loglevel
log.level = LogLevels.DEBUG;
// Write debug log
log.debug({ message: 'message' });

{
  "@timestamp": 1541421856291,
  "level": "DEBUG",
  "message": "Message",
}

Logging extra data

You can add any number of extra properties to the object when logging, like this:

// Setup so that the AWS Lambda meta data will be added to log output
  log.setup({ context, host: event.headers['Host'], verb: event.httpMethod, useragent: event.headers['User-Agent'], query: event.queryStringParameters, path: event.path, xRequestId: event.headers['X-REQUEST-ID'] });

// Write info log
log.info({ message: 'Message', myProp: 'hello', myNestedProp: {subProp: 'something'} });

{
  "@timestamp": 1541429192677,
  "level": "INFO",
  "message": "Message",
  "host": "abc123.execute-api.eu-west-1.amazonaws.com",
  "verb": "GET",
  "path": "/manage/health",
  "useragent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.77 Safari/537.36",
  "query": {
    "hello": "world"
  },
  "awsRequestId": "a3de505e-f16b-42f4-b3e6-bcd2e4a73903",
  "functionName": "ExampleCloudFormationStackName-ExampleLambdaFunctionResourceName-AULC3LB8Q02F",
  "functionVersion": "$LATEST",
  "invokedFunctionArn": "arn:aws:lambda:us-west-2:123456789012:function:ExampleCloudFormationStackName-ExampleLambdaFunctionResourceName-AULC3LB8Q02F",
  "memoryLimitInMB": 128,
  "remainingTime": 3,
  "myProp": "hello",
  "myNestedProp": {
    "subProp": "something"
  }
}

Pretty print

You can improve the appearance of logs when debugging, to make them easier to read. This will also add color to your logs if your terminal supports it.

To use, set the PN_LOG_PRETTY environment variable.

export PN_LOG_PRETTY=true

Mute all logs:

  log.level = LogLevels.OFF;

Set log level with environment variable

You can easily set the initial log level by setting the environment variable PN_LOG_LEVEL. This can be useful for setting different log levels in different environments TEST|PROD etc. Use 'OFF', 'DEBUG', 'INFO', 'WARN' or 'ERROR', like this:

PN_LOG_LEVEL: 'DEBUG'

Release process

When you are ready to release a version, take the following steps.

1. Bump the version in package.json according to semver. If we are making a non-breaking change, compared to the last version, the new version would be 0.12.0.

   "version": "0.11.0" to "version": "0.12.0"

2. Make a commit titled "Release version":

   git add package.json

   git commit -m "Release 0.12.0"

3. Tag your commit with the version, this is what triggers the deployment in Bitbucket Pipelines. The tagged commit must start with release-

   git tag -a "release-0.12.0" -m "Release 0.12.0"

4. Push to master!

   git push --follow-tags