Logging practices

This post covers some logging practices for the back-end (Node.js) apps.

• Avoid putting unique identifiers (e.g., user id) within the message. A unique id will produce a lot of different messages with the same context. Use it as a message parameter.

• Use the appropriate log level for the message. There are multiple log levels

  • info - app behavior, don't log every single step
  • error - app processing failure, something that needs to be fixed
  • debug - additional logs needed for troubleshooting
  • warning - something unexpected happened (e.g., third-party API fails)
  • fatal - app crash, needs to be fixed as soon as possible

Don't use the debug logs on production. Put log level as an environment variable.

• Stream logs to the standard output in JSON format so logging aggregators (Graylog, e.g.) can collect and adequately parse them

• Avoid logging any credentials, like passwords, auth tokens, etc.

• Put correlation ID as a message parameter for tracing related logs.

• Use a configurable logger like pino

const pino = require('pino');
const logger = pino({
  level: process.env.LOG_LEVEL || 'info',
  redact: {
    paths: ['token'],
    remove: true
  }
});
logger.info({ someId: 'id' }, 'Started the app...');
const correlationId = request.headers['correlation-id'] || uuid.v4();
logger.debug(
  { data: 'some data useful for debugging', correlationId },
  'Sending the request...'
);

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