How to use Winston in several modules?

Question

I have several modules - let\'s say server.js, module1.js,...,moduleN.js.

I would like define the log file in my server.js:

winston.add(winston.trans         


        

Answer 1

I use a factory function and pass in the module name so it can be added to the meta data:

logger-factory.js

const path = require('path');
const { createLogger, format, transports } = require('winston');
const { combine, errors, timestamp } = format;

const baseFormat = combine(
  timestamp({ format: 'YYYY-MM-DD HH:mm:ss' }),
  errors({ stack: true }),
  format((info) => {
    info.level = info.level.toUpperCase();
    return info;
  })(),
);

const splunkFormat = combine(
  baseFormat,
  format.json(),
);

const prettyFormat = combine(
  baseFormat,
  format.prettyPrint(),
);

const createCustomLogger = (moduleName) => createLogger({
  level: process.env.LOG_LEVEL,
  format: process.env.PRETTY_LOGS ? prettyFormat : splunkFormat,
  defaultMeta: { module: path.basename(moduleName) },
  transports: [
    new transports.Console(),
  ],
});

module.exports = createCustomLogger;

app-harness.js (so I can run the exported index module)

const index = require('./index');

// https://docs.aws.amazon.com/lambda/latest/dg/with-s3.html
const sampleEvent = {
  "Records": [
    {
      "eventVersion": "2.1",
      "eventSource": "aws:s3",
      "awsRegion": "us-east-2",
      "eventTime": "2019-09-03T19:37:27.192Z",
      "eventName": "ObjectCreated:Put",
      "userIdentity": {
        "principalId": "AWS:AIDAINPONIXQXHT3IKHL2"
      },
      "requestParameters": {
        "sourceIPAddress": "205.255.255.255"
      },
      "responseElements": {
        "x-amz-request-id": "D82B88E5F771F645",
        "x-amz-id-2": "vlR7PnpV2Ce81l0PRw6jlUpck7Jo5ZsQjryTjKlc5aLWGVHPZLj5NeC6qMa0emYBDXOo6QBU0Wo="
      },
      "s3": {
        "s3SchemaVersion": "1.0",
        "configurationId": "828aa6fc-f7b5-4305-8584-487c791949c1",
        "bucket": {
          "name": "lambda-artifacts-deafc19498e3f2df",
          "ownerIdentity": {
            "principalId": "A3I5XTEXAMAI3E"
          },
          "arn": "arn:aws:s3:::lambda-artifacts-deafc19498e3f2df"
        },
        "object": {
          "key": "b21b84d653bb07b05b1e6b33684dc11b",
          "size": 1305107,
          "eTag": "b21b84d653bb07b05b1e6b33684dc11b",
          "sequencer": "0C0F6F405D6ED209E1"
        }
      }
    }
  ]
};

index.handler(sampleEvent)
  .then(() => console.log('SUCCESS'))
  .catch((_) => console.log('FAILURE'));

index.js

const logger = require('./logger-factory')(__filename);
const app = require('./app');

exports.handler = async function (event) {
  try {
    logger.debug('lambda triggered with event', { event });
    await app.run(event);
    logger.debug(`lambda finished`);
  } catch(error) {
    logger.error('lambda failed: ', error);
    // rethrow the error up to AWS
    throw error;
  }
}

app.js

const logger = require('./logger-factory')(__filename);

const run = async (event) => {
  logger.info('processing S3 event', event);
  try {
    logger.info('reading s3 file')
    // throws because I used "Record" instead of "Records"
    const s3 = event.Record[0].s3;
    // use s3 to read the file
  } catch (error) {
    logger.error('failed to read from S3: ', error);
    throw error;
  }
};

module.exports = { run };

when I run the application locally at WARN level:

~/repos/ghe/lambda-logging (master * u=)> LOG_LEVEL=warn node -r dotenv/config ./src/app-harness.js
{
  module: 'app.js',
  level: 'ERROR',
  message: "failed to read from S3: Cannot read property '0' of undefined",
  stack: "TypeError: Cannot read property '0' of undefined\n" +
    '    at Object.run (/Users/jason.berk/repos/ghe/lambda-logging/src/app.js:8:28)\n' +
    '    at Object.exports.handler (/Users/jason.berk/repos/ghe/lambda-logging/src/index.js:7:15)\n' +
    '    at Object. (/Users/jason.berk/repos/ghe/lambda-logging/src/test-harness.js:44:7)\n' +
    '    at Module._compile (internal/modules/cjs/loader.js:1158:30)\n' +
    '    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1178:10)\n' +
    '    at Module.load (internal/modules/cjs/loader.js:1002:32)\n' +
    '    at Function.Module._load (internal/modules/cjs/loader.js:901:14)\n' +
    '    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:74:12)\n' +
    '    at internal/main/run_main_module.js:18:47',
  timestamp: '2020-05-11 17:34:06'
}
{
  module: 'index.js',
  level: 'ERROR',
  message: "lambda failed: Cannot read property '0' of undefined",
  stack: "TypeError: Cannot read property '0' of undefined\n" +
    '    at Object.run (/Users/jason.berk/repos/ghe/lambda-logging/src/app.js:8:28)\n' +
    '    at Object.exports.handler (/Users/jason.berk/repos/ghe/lambda-logging/src/index.js:7:15)\n' +
    '    at Object. (/Users/jason.berk/repos/ghe/lambda-logging/src/test-harness.js:44:7)\n' +
    '    at Module._compile (internal/modules/cjs/loader.js:1158:30)\n' +
    '    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1178:10)\n' +
    '    at Module.load (internal/modules/cjs/loader.js:1002:32)\n' +
    '    at Function.Module._load (internal/modules/cjs/loader.js:901:14)\n' +
    '    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:74:12)\n' +
    '    at internal/main/run_main_module.js:18:47',
  timestamp: '2020-05-11 17:34:06'
}

when I run at DEBUG level:

~/repos/ghe/lambda-logging (master * u=)> LOG_LEVEL=debug node -r dotenv/config ./src/test-harness.js 
{
  module: 'index.js',
  event: {
    Records: [
      {
        eventVersion: '2.1',
        eventSource: 'aws:s3',
        awsRegion: 'us-east-2',
        eventTime: '2019-09-03T19:37:27.192Z',
        eventName: 'ObjectCreated:Put',
        userIdentity: { principalId: 'AWS:AIDAINPONIXQXHT3IKHL2' },
        requestParameters: { sourceIPAddress: '205.255.255.255' },
        responseElements: {
          'x-amz-request-id': 'D82B88E5F771F645',
          'x-amz-id-2': 'vlR7PnpV2Ce81l0PRw6jlUpck7Jo5ZsQjryTjKlc5aLWGVHPZLj5NeC6qMa0emYBDXOo6QBU0Wo='
        },
        s3: {
          s3SchemaVersion: '1.0',
          configurationId: '828aa6fc-f7b5-4305-8584-487c791949c1',
          bucket: {
            name: 'lambda-artifacts-deafc19498e3f2df',
            ownerIdentity: { principalId: 'A3I5XTEXAMAI3E' },
            arn: 'arn:aws:s3:::lambda-artifacts-deafc19498e3f2df'
          },
          object: {
            key: 'b21b84d653bb07b05b1e6b33684dc11b',
            size: 1305107,
            eTag: 'b21b84d653bb07b05b1e6b33684dc11b',
            sequencer: '0C0F6F405D6ED209E1'
          }
        }
      }
    ]
  },
  level: 'DEBUG',
  message: 'lambda triggered with event',
  timestamp: '2020-05-11 17:38:21'
}
{
  module: 'app.js',
  Records: [
    {
      eventVersion: '2.1',
      eventSource: 'aws:s3',
      awsRegion: 'us-east-2',
      eventTime: '2019-09-03T19:37:27.192Z',
      eventName: 'ObjectCreated:Put',
      userIdentity: { principalId: 'AWS:AIDAINPONIXQXHT3IKHL2' },
      requestParameters: { sourceIPAddress: '205.255.255.255' },
      responseElements: {
        'x-amz-request-id': 'D82B88E5F771F645',
        'x-amz-id-2': 'vlR7PnpV2Ce81l0PRw6jlUpck7Jo5ZsQjryTjKlc5aLWGVHPZLj5NeC6qMa0emYBDXOo6QBU0Wo='
      },
      s3: {
        s3SchemaVersion: '1.0',
        configurationId: '828aa6fc-f7b5-4305-8584-487c791949c1',
        bucket: {
          name: 'lambda-artifacts-deafc19498e3f2df',
          ownerIdentity: { principalId: 'A3I5XTEXAMAI3E' },
          arn: 'arn:aws:s3:::lambda-artifacts-deafc19498e3f2df'
        },
        object: {
          key: 'b21b84d653bb07b05b1e6b33684dc11b',
          size: 1305107,
          eTag: 'b21b84d653bb07b05b1e6b33684dc11b',
          sequencer: '0C0F6F405D6ED209E1'
        }
      }
    }
  ],
  level: 'INFO',
  message: 'processing S3 event',
  timestamp: '2020-05-11 17:38:21'
}
{
  message: 'reading s3 file',
  level: 'INFO',
  module: 'app.js',
  timestamp: '2020-05-11 17:38:21'
}
{
  module: 'app.js',
  level: 'ERROR',
  message: "failed to read from S3: Cannot read property '0' of undefined",
  stack: "TypeError: Cannot read property '0' of undefined\n" +
    '    at Object.run (/Users/jason.berk/repos/ghe/lambda-logging/src/app.js:8:28)\n' +
    '    at Object.exports.handler (/Users/jason.berk/repos/ghe/lambda-logging/src/index.js:7:15)\n' +
    '    at Object. (/Users/jason.berk/repos/ghe/lambda-logging/src/test-harness.js:44:7)\n' +
    '    at Module._compile (internal/modules/cjs/loader.js:1158:30)\n' +
    '    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1178:10)\n' +
    '    at Module.load (internal/modules/cjs/loader.js:1002:32)\n' +
    '    at Function.Module._load (internal/modules/cjs/loader.js:901:14)\n' +
    '    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:74:12)\n' +
    '    at internal/main/run_main_module.js:18:47',
  timestamp: '2020-05-11 17:38:21'
}
{
  module: 'index.js',
  level: 'ERROR',
  message: "lambda failed: Cannot read property '0' of undefined",
  stack: "TypeError: Cannot read property '0' of undefined\n" +
    '    at Object.run (/Users/jason.berk/repos/ghe/lambda-logging/src/app.js:8:28)\n' +
    '    at Object.exports.handler (/Users/jason.berk/repos/ghe/lambda-logging/src/index.js:7:15)\n' +
    '    at Object. (/Users/jason.berk/repos/ghe/lambda-logging/src/test-harness.js:44:7)\n' +
    '    at Module._compile (internal/modules/cjs/loader.js:1158:30)\n' +
    '    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1178:10)\n' +
    '    at Module.load (internal/modules/cjs/loader.js:1002:32)\n' +
    '    at Function.Module._load (internal/modules/cjs/loader.js:901:14)\n' +
    '    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:74:12)\n' +
    '    at internal/main/run_main_module.js:18:47',
  timestamp: '2020-05-11 17:38:21'
}