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README.md

Appfirst

A statsd Ruby client for use with the AppFirst collector.

Statsd is a scheme developed by Etsy that provides a lightweight method of gathering statistics from your applications. The Appfirst version is based on the statsd Ruby client by reinh, but does not include the batch capability of the original. Instead, it includes an aggregation capability to reduce the amount of data that must be transported.

In the default case, data is sent to the AppFirst collector that is running on the same server as your application. The data is sent over a POSIX message queue. If the collector is not found, the client will fall back to the UDP transport method.

Installation:

The AppFirst Statsd client is packaged as a ruby gem. Installation should be as simple as:

$ gem install afstatsd

This should automatically install another gem, posix_mq. If the posix_mq fails during installation, it is probably because your ruby installation does not include the development package (eg ruby1.9-devel).

Configuration:

Pull in the AppFirst Statsd Client (probably in your main module):

require 'afstatsd'

At startup, instantiate a Statsd client object. To use the default configuration which aggregates metrics for 20 seconds and then sends data to the AppFirst collector, you should instantiate the client object like so:

$statsd = Statsd.new

To add a UDP fall-back, include the host and port of the fall-back server:

$statsd = Statsd.new 'localhost', 8125

Or, to only use UDP, set the aggregation period to 0 and specify the 'udp' parameter like so:

$statsd = Statsd.new 'localhost', 8125, 0, 'udp'

The client object in this example is a global for convenience, but this is not a requirement. The third parameter is the timing interval for metric aggregation, and defaults to 20 sec.

The aggregation feature will collect statistics over a period of time, and aggregate them to reduce the amount of data that needs to be transferred. For example, if an individual counter is incremented 1000 times during the aggregation interval, only one message will be sent with a count of 1000, rather than 1000 messages with count of 1. The tradeoff is that latency is introduced in reporting the metrics.

Aggregation is turned on by default, and we highly recommend it, but it can be disabled by setting the interval to 0, or by setting the aggregating attribute to false:

$statsd.aggregating = false

The message queue is configured by the AppFirst collector. At the current time, it is set accept about 200 messages per second. If overrun, messages will be dropped. This is another reason to use the aggregation capability. Dropped messages are counted and can be accessed with the $statsd.dropped attribute.

The namespace attribute, if specified, will be prepended to all metrics, for example:

$statsd.namespace = 'system.component'

or perhaps:

$statsd.namespace = 'system.#{Socket.gethostname}.component'

This Statsd client can also send data the 'Etsy standard' way using a UDP socket. This can be useful if transitioning from some other StatsD implementation to the AppFirst implementation:

$statsd.set_transport(:udp_transport)

If the message queue is not found, the client will revert to using a UDP socket as a backup transport method. The only reason this should happen is if the AppFirst collector is not installed.

Once these configuration attributes are set, the client is thread-safe for general usage.

Usage:

Now comes the fun part. Just sprinkle these one-liners throughout your application code to report metrics to your AppFirst application or dashboard:

Counters

def increment(name, sample_rate=1)
def decrement(stat, sample_rate=1)
def count(stat, count, sample_rate=1)

Timers

def timing(stat, ms, sample_rate=1)
def time(stat, sample_rate=1)

Gauges

def gauge(stat, value)

Examples:

$statsd.increment 'foo'                              # increment event counter 'foo'.
$statsd.decrement 'manchu'                           # decrement event counter 'manchu'.
$statsd.count 'mustache', 10                         # report that event 'mustache' ocurred 10 times.
$statsd.gauge 'buffers_left', buffer_pool.count      # report a value as a guage
$statsd.time 'cart_process_time' {cart_processing}   # will report the execution time of a block

The easiest Statsd method to use is increment. You don't have to track anything yourself in your application. Just fire off that one-liner for every event, you want to monitor, and the upstream apparatus will take care of everything for you.

If you want to keep track of the current state of a value, you should report that with a gauge.

To report how long something took to execute, use the time metric.

Logging:

To attach a logger to the Statsd client:

require 'logger'
#...
Statsd.logger ||= Logger.new 'afstatsd.log'
Statsd.logger.level = Logger::DEBUG

Copyright (c) 2013 AppFirst

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

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