winston-loki

A Grafana Loki transport for the nodejs logging library Winston.

Usage

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

Examples

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.

Options

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	http://127.0.0.1:3100	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

Example (Running Loki Locally)

With default formatting:

const { createLogger, transports } = require("winston");
const LokiTransport = require("winston-loki");
const options = {
  ...,
  transports: [
    new LokiTransport({
      host: "http://127.0.0.1:3100"
    })
  ]
  ...
};
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

Example (Grafana Cloud Loki)

Important: this snippet requires the following values, here are the instructions for how you can find them.

LOKI_HOST: find this in your Grafana Cloud instance by checking Connections > Data Sources, find the right Loki connection, and copy its URL, which may look like https://logs-prod-006.grafana.net
USER_ID: the user number in the same data source definition, it will be a multi-digit number like 372040
GRAFANA_CLOUD_TOKEN: In Grafana Cloud, search for Cloud Access Policies. Create a new Cloud Access Policy, ensuring its scopes include logs:write. Generate a token for this cloud access policy, and use this value here.

const { createLogger, transports } = require("winston");
const LokiTransport = require("winston-loki");
const options = {
  ...,
  transports: [
    new LokiTransport({
        host: 'LOKI_HOST',
        labels: { app: 'my-app' },
        json: true,
        basicAuth: 'USER_ID:GRAFANA_CLOUD_TOKEN',
        format: winston.format.json(),
        replaceTimestamp: true,
        onConnectionError: (err) => console.error(err),
    })
  ]
  ...
};
const logger = createLogger(options);
logger.debug({ message: 'test', labels: { 'key': 'value' } })

Developing

Requirements

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.

Example

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.