Candies

Invisible image based tracing service with Redis backend

Requirements

Candies uses redis as a datastore.

Candies only supports redis 2.0 or greater.

If you're on OS X, Homebrew is the simplest way to install Redis:

$ brew install redis
$ redis-server /usr/local/etc/redis.conf

You now have a Redis daemon running on 6379.

Setup

If you are using bundler add candies to your Gemfile:

gem 'candies'

Then run:

bundle install

Otherwise install the gem:

gem install candies

and require it in your project:

require 'candies'

Usage

Standalone service

Candies can be deployed as a standalone service (for example to heroku). To do it create a simple config.ru file:

require 'rubygems'
require 'candies'

# Candies.redis = ENV['REDISTOGO_URL'], read below about redis configuration

run Candies::Server.new

and deploy it to any rack compatybile environment (passenger, thin, unicorn, etc.)

Mounted to the Rails app

Mount Candies in your config/routes.rb file:

mount Candies::Server.new => "candies", :as => "candies"

It will be available under http://yourapproot.tld/candies url

Image tag

When you have Candies server deployed you can add tracking payload by including img tag in your HTML code:

<a href="http://candies.tld/anyfile.gif?id=tracing-id&foo=bar&baz=foo" />

or if you mounted candies in your rails app as candies then it will be:

<a href="http://yourapproot.tld/candies/anyfile.gif?id=tracing-id&foo=bar&baz=foo" />

Also in rails app you can use candies_image_tag helper. To do so you have to set Candies.url to point to the candies service url. The best way is to put in config/initializers/candies.rb file:

Candies.host = "http://yourapproot.tld/candies"

Now you can use candies_image_tag helper in controller views and in mailer views. Example:

<%= candies_image_tag(:id => "[email protected]", :email_type => "hello") %>

Note that id parameter is required. It will be used to create a redis key under which paload will be stored. In this case redis key will be: candies:[email protected]:2011-11-10T13:13:09+01:00 and value: "{\"email_type\":\"hello\"}". If you don't specify id parameter not value will be stored. Invisible image will by served anyway.

Configuration

Redis

You may want to change the Redis host and port Candies connects to, or set various other options at startup.

Candies has a redis setter which can be given a string or a Redis object. This means if you're already using Redis in your app, Candies can re-use the existing connection.

String: Candies.redis = 'localhost:6379'

Redis: Candies.redis = $redis

For our rails app we have a config/initializers/candies.rb file where we load config/candies.yml by hand and set the Redis information appropriately.

Here's our config/redis.yml:

development: localhost:6379
test: localhost:6379
staging: redis1.example.com:6379
fi: localhost:6379
production: redis1.example.com:6379

And our initializer:

rails_root = ENV['RAILS_ROOT'] || File.dirname(__FILE__) + '/../..'
rails_env = ENV['RAILS_ENV'] || 'development'

redis_config = YAML.load_file(rails_root + '/config/redis.yml')
Candies.redis = redis_config[rails_env]

Namespaces

If you're running multiple, separate instances of candies you may want to namespace the keyspaces so they do not overlap. This is not unlike the approach taken by many memcached clients.

This feature is provided by the [redis-namespace][rs] library, which candies uses by default to separate the keys it manages from other keys in your Redis server.

Simply use the Candies.redis.namespace accessor:

Candies.redis.namespace = "candies:blog"

We recommend sticking this in your initializer somewhere after Redis is configured.

Results

There isn't any dashboard for displaying values (yet). You cen review them by logging into redis-cli. Sorry.

Development

Source hosted at GitHub. Report Issues/Feature requests on GitHub Issues.

Tests can be ran with rake test

Note on Patches/Pull Requests

Fork the project.
Make your feature addition or bug fix.
Add tests for it. This is important so I don't break it in a future version unintentionally.
Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
Send me a pull request. Bonus points for topic branches.