ECS Logging with Winston

This Node.js package provides a formatter for the winston logger, compatible with Elastic Common Schema (ECS) logging. In combination with the Filebeat shipper, you can monitor all your logs in one place in the Elastic Stack. winston 3.x versions >=3.3.3 are supported.

$ npm install @elastic/ecs-winston-format

const winston = require('winston');
const { ecsFormat } = require('@elastic/ecs-winston-format');

const logger = winston.createLogger({
  format: ecsFormat(/* options */), 
  transports: [
    new winston.transports.Console()
  ]
});

logger.info('hi');
logger.error('oops there is a problem', { err: new Error('boom') });

The best way to collect the logs once they are ECS-formatted is with Filebeat:

filebeat.inputs:
- type: filestream 
  paths: /path/to/logs.json
  parsers:
    - ndjson:
      overwrite_keys: true 
      add_error_key: true 
      expand_keys: true 

processors: 
  - add_host_metadata: ~
  - add_cloud_metadata: ~
  - add_docker_metadata: ~
  - add_kubernetes_metadata: ~

filebeat.inputs:
- type: log
  paths: /path/to/logs.json
  json.keys_under_root: true
  json.overwrite_keys: true
  json.add_error_key: true
  json.expand_keys: true

processors:
- add_host_metadata: ~
- add_cloud_metadata: ~
- add_docker_metadata: ~
- add_kubernetes_metadata: ~

annotations:
  co.elastic.logs/json.overwrite_keys: true 
  co.elastic.logs/json.add_error_key: true 
  co.elastic.logs/json.expand_keys: true 

labels:
  co.elastic.logs/json.overwrite_keys: true 
  co.elastic.logs/json.add_error_key: true 
  co.elastic.logs/json.expand_keys: true 

For more information, see the Filebeat reference.

const winston = require('winston');
const { ecsFormat } = require('@elastic/ecs-winston-format');

const logger = winston.createLogger({
  level: 'info',
  format: ecsFormat(/* options */), 
  transports: [
    new winston.transports.Console()
  ]
});

logger.info('hi');
logger.error('oops there is a problem', { foo: 'bar' });

Running this script (available here) will produce log output similar to the following:

% node examples/basic.js
{"@timestamp":"2023-10-14T02:14:17.302Z","log.level":"info","message":"hi","ecs.version":"8.10.0"}
{"@timestamp":"2023-10-14T02:14:17.304Z","log.level":"error","message":"oops there is a problem","ecs.version":"8.10.0","foo":"bar"}

The formatter handles serialization to JSON, so you don’t need to add the json formatter. As well, a timestamp is automatically generated by the formatter, so you don’t need to add the timestamp formatter.

By default, the formatter will convert an err meta field that is an Error instance to ECS Error fields. For example:

const winston = require('winston');
const { ecsFormat } = require('@elastic/ecs-winston-format');
const logger = winston.createLogger({
  format: ecsFormat(), 
  transports: [
    new winston.transports.Console()
  ]
});

const myErr = new Error('boom');
logger.info('oops', { err: myErr }); 

will yield (pretty-printed for readability):

% node examples/error.js | jq .
{
  "@timestamp": "2021-01-26T17:25:07.983Z",
  "log.level": "info",
  "message": "oops",
  "error": {
    "type": "Error",
    "message": "boom",
    "stack_trace": "Error: boom\n    at Object.<anonymous> (..."
  },
  "ecs.version": "8.10.0"
}

Special handling of the err meta field can be disabled via the convertErr: false option:

...
const logger = winston.createLogger({
  format: ecsFormat({ convertErr: false }),
...

With the convertReqRes: true option, the formatter will automatically convert Node.js core request and response objects when passed as the req and res meta fields, respectively.

const http = require('http');
const winston = require('winston');
const { ecsFormat } = require('@elastic/ecs-winston-format');

const logger = winston.createLogger({
  level: 'info',
  format: ecsFormat({ convertReqRes: true }), 
  transports: [
    new winston.transports.Console()
  ]
});

const server = http.createServer(handler);
server.listen(3000, () => {
  logger.info('listening at http://localhost:3000')
});

function handler (req, res) {
  res.setHeader('Foo', 'Bar');
  res.end('ok');
  logger.info('handled request', { req, res }); 
}

This will produce logs with request and response info using ECS HTTP fields. For example:

% node examples/http.js | jq .    # using jq for pretty printing
...                               # run 'curl http://localhost:3000/'
{
  "@timestamp": "2023-10-14T02:15:54.768Z",
  "log.level": "info",
  "message": "handled request",
  "http": {
    "version": "1.1",
    "request": {
      "method": "GET",
      "headers": {
        "host": "localhost:3000",
        "user-agent": "curl/8.1.2",
        "accept": "*/*"
      }
    },
    "response": {
      "status_code": 200,
      "headers": {
        "foo": "Bar"
      }
    }
  },
  "url": {
    "path": "/",
    "full": "http://localhost:3000/"
  },
  "client": {
    "address": "::ffff:127.0.0.1",
    "ip": "::ffff:127.0.0.1",
    "port": 49538
  },
  "user_agent": {
    "original": "curl/8.1.2"
  },
  "ecs.version": "8.10.0"
}

This ECS log formatter integrates with Elastic APM. If your Node app is using the Node.js Elastic APM Agent, then a number of fields are added to log records to correlate between APM services or traces and logging data:

For example, running examples/http-with-elastic-apm.js and curl -i localhost:3000/ results in a log record with the following:

% node examples/http-with-elastic-apm.js | jq .
...
  "service.name": "http-with-elastic-apm",
  "service.version": "1.4.0",
  "service.environment": "development",
  "event.dataset": "http-with-elastic-apm"
  "trace.id": "7fd75f0f33ff49aba85d060b46dcad7e",
  "transaction.id": "6c97c7c1b468fa05"
}

These IDs match trace data reported by the APM agent.

Integration with Elastic APM can be explicitly disabled via the apmIntegration: false option, for example:

const logger = winston.createLogger({
  format: ecsFormat({ apmIntegration: false }),
  // ...
})

The ecs-logging spec suggests that the first three fields in log records should be @timestamp, log.level, and message. As of version 1.5.0, this formatter does not follow this suggestion. It would be possible but would require creating a new Object in ecsFields for each log record. Given that ordering of ecs-logging fields is for human readability and does not affect interoperability, the decision was made to prefer performance.

Create a formatter for winston that emits in ECS Logging format. This is a single format that handles both ecsFields([options]) and ecsStringify([options]). The following two are equivalent:

const { ecsFormat, ecsFields, ecsStringify } = require('@elastic/ecs-winston-format');
const winston = require('winston');

const logger = winston.createLogger({
  format: ecsFormat(/* options */),
  // ...
});

const logger = winston.createLogger({
  format: winston.format.combine(
    ecsFields(/* options */),
    ecsStringify()
  ),
  // ...
});

Create a formatter for winston that converts fields on the log record info object to ECS Logging format.

Create a formatter for winston that stringifies/serializes the log record to JSON.

This is similar to logform.json(). They both use the safe-stable-stringify package to produce the JSON. Some differences: