UDPLog documentation

UDPLog is a system for emitting application log events via UDP and shipping them via RabbitMQ or Scribe for further processing. The idea is that the applications sends its structured log events to a dedicated shipping daemon on the same machine, which in turn passes it on to one or more remote services. As this uses UDP, emitting events is non-blocking fire-and-forget. A system like Logstash can then be used to process and store log events.


The U in UDPLog stands for unreliable, and that’s just what it is. Log messages are delivered on a best-effort basis and are not guaranteed in any way, even though the default mode is to send logs to a daemon running on the same machine.

Do not use UDPLog for any data that must be reliable, such as any information used for billing of any sort!



A log event a combination of a category identifier (ASCII, matching the regular expression ^[0-9A-Za-z_]+$) and a set of name/value pairs. The UDP wire protocol represents an event as a single datagram composed of the the category, a colon character, an optional whitespace character and the name/value pairs rendered as a JSON object:

some_category: {"a_key": "a_value", timestamp: "1379002018.000"}

What to log and what to call it

Log everything. It’s better to over-log than under-log.

In general, it is better to have to fewer distinct categories, and to have multiple types of entries in the same category if they have common fields. Using ElasticSearch and Logstash, you can then define a mapping for each category. To distinguish the events in the same category, you can add another field like event.

In general, an application shouldn’t have more than a few categories, and categories can span multiple applications.

The UDPLog libraries already adds a timestamp to each event. You do not need to add a timestamp to your logs, unless you want to record the exact time your event happened as opposed to the time the log was created. In that case, set the timestamp field.

All times should be expressed in seconds, not micro or milliseconds. Generally, you’ll want a floating point number of seconds. Timestamps are expressed as floating point seconds since the UNIX epoch.

Emitting log events

There are a several ways to emit log events from applications:

  • With direct calls to the logger.
  • Via the Python logging facility.
  • Via the Twisted logging system.

See client for details.

Receiving log events

To ship log events to Scribe and/or RabbitMQ, there is Twisted-based support for receiving UDPLog events and passing them to those systems. This is exposed via a twistd plugin called udplog.

Pass all events to a local Scribe service:

twistd udplog --scribe-host=localhost

Pass all events to a RabbitMQ server, using the exchange named logs:

twistd udplog --rabbitmq-host= --rabbitmq-exchange=logs

For a full list of command line options, run:

twistd udplog --help


To capture logs during application development, run a UDPLog daemon. This will print to the console all messages it receives:

python -mudplog.udplog

Or, using the twistd plugin:

twistd -n udplog --verbose

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