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 */), 1
  transports: [
    new winston.transports.Console()
  ]
});

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

1. Pass the ECS formatter to winston here.

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

filebeat.inputs:
- type: filestream 1
  paths: /path/to/logs.json
  parsers:
    - ndjson:
      overwrite_keys: true 2
      add_error_key: true 3
      expand_keys: true 4

processors: 5
  - 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 1
  co.elastic.logs/json.add_error_key: true 2
  co.elastic.logs/json.expand_keys: true 3

labels:
  co.elastic.logs/json.overwrite_keys: true 1
  co.elastic.logs/json.add_error_key: true 2
  co.elastic.logs/json.expand_keys: true 3

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 */), 1
  transports: [
    new winston.transports.Console()
  ]
});

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

1. See available options below.

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 }), 1
  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 }); 2
}

1. use convertReqRes option
2. log req and/or res meta fields

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

% node examples/http.js | jq .   1
...                               # 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"
}

1. using jq for pretty printing

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:

• Log statements (e.g. logger.info(...)) called when there is a current tracing span will include tracing fields — trace.id, transaction.id, span.id.
• A number of service identifier fields determined by or configured on the APM agent allow cross-linking between services and logs in Kibana — service.name, service.version, service.environment, service.node.name.
• event.dataset enables log rate anomaly detection in the Elastic Observability app.

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.

• options {type-object} The following options are supported:

  • convertErr {type-boolean} Whether to convert a logged err field to ECS error fields. Default: true.
  • convertReqRes {type-boolean} Whether to logged req and res HTTP request and response fields to ECS HTTP, User agent, and URL fields. Default: false.
  • apmIntegration {type-boolean} Whether to enable APM agent integration. Default: true.
  • serviceName {type-string} A "service.name" value. If specified this overrides any value from an active APM agent.
  • serviceVersion {type-string} A "service.version" value. If specified this overrides any value from an active APM agent.
  • serviceEnvironment {type-string} A "service.environment" value. If specified this overrides any value from an active APM agent.
  • serviceNodeName {type-string} A "service.node.name" value. If specified this overrides any value from an active APM agent.
  • eventDataset {type-string} A "event.dataset" value. If specified this overrides the default of using ${serviceVersion}.

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()
  ),
  // ...
});

• options {type-object} The following options are supported:

  • convertErr {type-boolean} Whether to convert a logged err field to ECS error fields. Default: true.
  • convertReqRes {type-boolean} Whether to logged req and res HTTP request and response fields to ECS HTTP, User agent, and URL fields. Default: false.
  • apmIntegration {type-boolean} Whether to enable APM agent integration. Default: true.
  • serviceName {type-string} A "service.name" value. If specified this overrides any value from an active APM agent.
  • serviceVersion {type-string} A "service.version" value. If specified this overrides any value from an active APM agent.
  • serviceEnvironment {type-string} A "service.environment" value. If specified this overrides any value from an active APM agent.
  • serviceNodeName {type-string} A "service.node.name" value. If specified this overrides any value from an active APM agent.
  • eventDataset {type-string} A "event.dataset" value. If specified this overrides the default of using ${serviceVersion}.

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:

• This stringifier skips serializing the level field, because it is not an ECS field.
• Winston provides a replacer that converts bigints to strings The argument for doing so is that a JavaScript JSON parser looses precision when parsing a bigint. The argument against is that a BigInt changes type to a string rather than a number. For now this stringifier does not convert BitInts to strings.