Using Node.js

The Bunyan library is a logger for JavaScript with wide platform support and good facilities for structured log messages. The bunyan-seq package is a plug-in for Bunyan that batches log events and posts the to the Seq HTTP ingestion API.

Getting started

First, install both the bunyan and bunyan-seq packages.

npm install --save bunyan
npm install --save bunyan-seq

When configuring the Bunyan logger, pass a Seq stream using createStream():

let bunyan = require('bunyan');
let seq = require('bunyan-seq');

var log = bunyan.createLogger({
    name: 'myapp',
    streams: [
        {
            stream: process.stdout,
            level: 'warn',
        },
        seq.createStream({
            serverUrl: 'http://localhost:5341',
            level: 'info'
        })
    ]
});

log.info('Hi!');
log.warn({lang: 'fr'}, 'Au revoir');

Configuration

The createStream() method accepts a configuration object with the following parameters. No parameters are required.

Parameter	Default	Description
`apiKey`		The API Key to use when connecting to Seq
`batchSizeLimit`	1048576 (1 MiB)	The maximum batch size to send to Seq (should not exceed Settings > System > Raw ingestion payload limit)
`eventSizeLimit`	262144 (256 kiB)	The maximum event size to send to Seq; larger events will be dumped to stdout (should match Settings > System > Raw event body limit)
`level`		The Bunyan logging level for the stream
`maxBatchingTime`	2000	The time in milliseconds that the logger will wait for additional events before sending a batch to Seq
`name`		The Bunyan stream name, which can be used when configuring Bunyan filters
`onError`	Log to console	A function to receive any errors raised when sending events to Seq
`reemitErrorEvents`	false	If `true`, error events raised by the stream will propagate as `'error'` events on the Bunyan logger object.
`serverUrl`	http://localhost:5341	The HTTP endpoint address of the Seq server

Message templates

You can specify property names as tokens in the log message to control how the event is rendered in Seq:

log.info({user: 'Alice'}, 'Hi, {user}!');

It is not necessary to specify tokens for all properties, but using this technique instead of string formatting will produce more easily machine-readable log events by associating the same template, and thus the same event id, with related events.