A Logger for the Cloudflare workers environment that sends the logs to grafana loki

Install

npm install workers-loki-logger

Usage

When creating a logger and writing to it all logs are first stored in memory. It is sent to loki when the flush method is called.
It is recommended to use a wrapper function for the logger to ensure that the logs are flushed to loki.

Example with wrapper function

Features

• Send logs to loki
• Format exceptions as string
• MDC to add additional information to the logs

API

new Logger()

Creates a new logger

import {Logger} from 'workers-loki-logger';

new Logger({
  cloudflareContext: context, // Cloudflare context if this option is set it will use the waitUntil function on flush
  lokiSecret: 'some-secret', // Secret for loki authentication
  lokiUrl: 'https://logs-prod-eu-west-0.grafana.net', // Url to loki
  stream: { // Stream options for loki
    worker: 'esm-worker-simple',
    environment: 'development',
  },
  mdc: { // If this option is set it will be used as the initial value for the MDC
    requestPath: '/some/path',
  }
});

logger.{info,warn,error,fatal}()

Write log

import {Logger} from 'workers-loki-logger';

declare const logger: Logger;

logger.info('message');

logger.warn('message');
logger.warn('message', new Error('some error'));

logger.error('message');
logger.error('message', new Error('some error'));

logger.fatal('message');
logger.fatal('message', new Error('some error'));

logger.{mdcSet,mdcDelete,mdcGet}()

Change MDC

import {Logger} from 'workers-loki-logger';

declare const logger: Logger;

logger.mdcSet('key', 'value');
logger.mdcGet('key');
logger.mdcDelete('key');

logger.flush()

Write logs to loki

import {Logger} from 'workers-loki-logger';

declare const logger: Logger;

await logger.flush();

Example

Example with wrapper function

import {Logger} from 'workers-loki-logger';

function getLogger(context: ExecutionContext, lokiSecret: string) {
  return new Logger({
    cloudflareContext: context,
    lokiSecret,
    lokiUrl: 'https://logs-prod-eu-west-0.grafana.net',
    stream: {
      worker: 'esm-worker-simple',
      environment: 'development',
    }
  });
}

type Environment = {
  LOKI_SECRET: string
}

// This function could be moved to a separate file and imported by multiple workers
function onFetch(handler: (request: Request, environment: Environment, context: ExecutionContext, logger: Logger) => Promise<Response>) {
  return async (request: Request, environment: Environment, context: ExecutionContext) => {
    const logger = getLogger(context, environment.LOKI_SECRET);
    logger.mdcSet('requestUrl', request.url);
    let response;
    try {
      response = await handler(request, environment, context, logger);
    } catch (error) {
      logger.error('Caught error', error);
      response = new Response('Internal Server Error', {status: 500});
    } finally {
      await logger.flush();
    }
    return response;
  };
}

export default {
  fetch: onFetch(async (request, environment, context, logger) => {
    logger.info('Request received' + request.url);
    return await fetch(request);
  })
};

Example with manually calling flush

import {Logger} from 'workers-loki-logger';

function getLogger(context: ExecutionContext, lokiSecret: string) {
  return new Logger({
    cloudflareContext: context,
    lokiSecret,
    lokiUrl: 'https://logs-prod-eu-west-0.grafana.net',
    stream: {
      worker: 'esm-worker-simple',
      environment: 'development',
    }
  });
}

export default {
  async fetch(request: Request, environment: { LOKI_SECRET: string }, context: ExecutionContext) {
    const logger = getLogger(context, environment.LOKI_SECRET);
    logger.mdcSet('requestUrl', request.url);
    logger.info('Request received' + request.url);
    let response;
    try {
      response = await fetch(request);
    } catch (error) {
      logger.error('Caught error', error);
      response = new Response('Internal Server Error', {status: 500});
    } finally {
      await logger.flush();
    }
    return response;
  }
};

Run tests

npm test

Me

👤 Donato Wolfisberg ([email protected]) @SirCremefresh