This is an optional appender for log4js-node.

npm install @log4js-node/gelf

The GELF appender supports sending log messages over UDP to a GELF compatible server such as Graylog. It uses node's core UDP support and does not require any other dependencies. If you use this appender, remember to call log4js.shutdown when your application terminates, so that all messages will have been sent to the server and the UDP socket can be closed. The appender supports passing custom fields to the server in both the config, and in individual log messages (see examples below).

• type - @log4js-node/gelf
• host - string (defaults to localhost) - the gelf server hostname
• port - integer (defaults to 12201) - the port the gelf server is listening on
• hostname - string (defaults to OS.hostname()) - the hostname used to identify the origin of the log messages.
• facility - string (optional)
• customFields - object (optional) - fields to be added to each log message; custom fields must start with an underscore.

log4js.configure({
  appenders: {
    gelf: { type: '@log4js-node/gelf' }
  },
  categories: {
    default: { appenders: ['gelf'], level: 'info' }
  }
});

This will send log messages to a server at localhost:12201.

log4js.configure({
  appenders: {
    gelf: { type: '@log4js-node/gelf', host: 'gelf.server', customFields: { '_something': 'yep' } }
  },
  categories: {
    default: { appenders: ['gelf'], level: 'info' }
  }
});

This will result in all log messages having the custom field _something set to 'yep'.

log4js.configure({
  appenders: {
    gelf: { type: '@log4js-node/gelf', customFields: { '_thing': 'isathing' } }
  },
  categories: {
    default: { appenders: ['gelf'], level: 'info' }
  }
});
const logger = log4js.getLogger();
logger.error({ GELF: true, _thing2: 'alsoathing' }, 'oh no, something went wrong');

This will result in a log message with the custom fields _thing and _thing2. Note that log message custom fields will override config custom fields.