A Winston transport for Grafana Loki

winston, winston-transport, transport, loki, grafana, logging, plugin, SRE, site reliability engineering, grafana loki, grafana-loki, winston-loki
npm install winston-loki@2.1.2



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A Grafana Loki transport for the nodejs logging library Winston.


This Winston transport is used similarly to other Winston transports. Require winston and define a new LokiTransport() inside its options when creating it.

Several usage examples with a test configuration for Grafana+Loki+Promtail reside under examples/. If you want the simplest possible configuration, that's probably the place to check out. By defining json: true and giving winston-loki the correct host address for Loki is enough for most.


LokiTransport() takes a Javascript object as an input. These are the options that are available, required in bold:

Parameter Description Example Default
host URL for Grafana Loki null
interval The interval at which batched logs are sent in seconds 30 5
json Use JSON instead of Protobuf for transport true false
batching If batching is not used, the logs are sent as they come true true
clearOnError Discard any logs that result in an error during transport true false
replaceTimestamp Replace any log timestamps with Date.now(). Warning: Disabling replaceTimestamp may result in logs failing to upload due to recent changes in the upstream Loki project. It is recommended to leave this option enabled unless you have a specific reason to disable it. true true
labels custom labels, key-value pairs { module: 'http' } undefined
format winston format (https://github.com/winstonjs/winston#formats) simple() undefined
gracefulShutdown Enable/disable graceful shutdown (wait for any unsent batches) false true
timeout timeout for requests to grafana loki in ms 30000 undefined
basicAuth basic authentication credentials to access Loki over HTTP username:password undefined
onConnectionError Loki error connection handler (err) => console.error(err) undefined
useWinstonMetaAsLabels Use Winston's "meta" (such as defaultMeta values) as Loki labels true false
ignoredMeta When useWinstonMetaAsLabels is enabled, a list of meta values to ignore ["error_description"] undefined


With default formatting:

const { createLogger, transports } = require("winston");
const LokiTransport = require("winston-loki");
const options = {
  transports: [
    new LokiTransport({
      host: ""
const logger = createLogger(options);

You can set custom labels in every log as well like this:

logger.debug({ message: 'test', labels: { 'key': 'value' } })

TODO: Add custom formatting example



Running a local Loki for testing is probably required, and the easiest way to do that is to follow this guide: https://github.com/grafana/loki/tree/master/production#run-locally-using-docker. After that, Grafana Loki instance is available at http://localhost:3100, with a Grafana instance running at http://localhost:3000. Username admin, password admin. Add the Loki source with the URL http://loki:3100, and the explorer should work.

Refer to https://grafana.com/docs/loki/latest/api/ for documentation about the available endpoints, data formats etc.


npm install
npm link
cd ~/your_project
npm link winston-loki
npm install

And you should have a working, requirable winston-loki package under your project's node_modules. After the link has been established, any changes to winston-loki should show on rerun of the software that uses it.

Run tests

npm test

Write new ones under /test