Log4JS - GELF appender

This is an optional appender for log4js-node.
``bash 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).

`Configuration`

* 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.

`Example (default config)`

javascript
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

.
Example (custom fields in config)

javascript
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'.
Example (custom fields in log message)

javascript
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.