Log to a central MongoDB from Rails apps.

1. If using Bundler, add the following to your Gemfile then refresh your dependencies by executing "bundle install":

    gem "central_logger"
   

2. If you're just using gem:

    gem install central_logger
   

3. Add the following line to your ApplicationController:

    include CentralLogger::Filter
   

4. If using Rails 3, SKIP this step. Otherwise, add the following to config/environment.rb:

    require 'central_logger'
    CentralLogger::Initializer.initialize_deprecated_logger(config)
   

5. Add mongo settings to database.yml for each environment in which you want to use the Central Logger. The central logger will also look for a separate central_logger.yml or mongoid.yml (if you are using mongoid) before looking in database.yml. In the central_logger.yml and mongoid.yml case, the settings should be defined without the 'mongo' subkey.

   database.yml:

    development:
      adapter: mysql
      database: my_app_development
      user: root
      mongo:
        database: my_app               # required (the only required setting)
        capsize: <%= 10.megabytes %>   # default: 250MB for production; 100MB otherwise
        host: localhost                # default: localhost
        port: 27017                    # default: 27017
        replica_set: true              # default: false - Adds retries for ConnectionFailure during voting for replica set master
        safe_insert: true              # default: false - Enable/Disable safe inserts (wait for insert to propagate to all nodes)
        application_name: my_app       # default: Rails.application - Only really needed for non-capistrano Rails 2 deployments. Otherwise should set automatically.
   

   central_logger.yml:

    development:
      database: my_app
      capsize: <%= 10.megabytes %>
      host: localhost
      port: 27017
      replica_set: true
   

With that in place, a new MongoDB document (record) will be created for each request and, by default will record the following information: Runtime, IP Address, Request Time, Controller, Action, Params, Application Name and All messages sent to the logger. The structure of the Mongo document looks like this:

    {
      'action'           : action_name,
      'application_name' : application_name (rails root),
      'controller'       : controller_name,
      'ip'               : ip_address,
      'messages'         : {
                             'info'  : [ ],
                             'debug' : [ ],
                             'error' : [ ],
                             'warn'  : [ ],
                             'fatal' : [ ]
                           },
      'params'           : { },
      'path'             : path,
      'request_time'     : date_of_request,
      'runtime'          : elapsed_execution_time_in_milliseconds,
      'url'              : full_url
    }

Beyond that, if you want to add extra information to the base of the document (let's say something like user_guid on every request that it's available), you can just call the Rails.logger.add_metadata method on your logger like so (for example from a before_filter):

    # make sure we're using the CentralLogger in this environment
    if Rails.logger.respond_to?(:add_metadata)
      Rails.logger.add_metadata(:user_guid => @user_guid)
    end

Please see the central_log_viewer: a companion web application for querying and viewing your centralized logs.

And now, for a couple quick examples on getting ahold of this log data... First, here's how to get a handle on the MongoDB from within a Rails console:

>> db = Rails.logger.mongo_connection
=> #<Mongo::DB:0x102f19ac0 @slave_ok=nil, @name="my_app" ... >

>> collection = db[Rails.logger.mongo_collection_name]
=> #<Mongo::Collection:0x1031b3ee8 @name="development_log" ... >

Once you've got the collection, you can find all requests for a specific user (with guid):

>> cursor = collection.find(:user_guid => '12355')
=> #<Mongo::Cursor:0x1031a3e30 ... >
>> cursor.count
=> 5

Find all requests that took more that one second to complete:

>> collection.find({:runtime => {'$gt' => 1000}}).count
=> 3

Find all order#show requests with a particular order id (id=order_id):

>> collection.find({"controller" => "order", "action"=> "show", "params.id" => order_id})

Find all requests with an exception that contains "RoutingError" in the message or stack trace:

>> collection.find({"messages.error" => /RoutingError/})

Find all requests with a request_date greater than '11/18/2010 22:59:52 GMT'

>> collection.find({:request_time => {'$gt' => Time.utc(2010, 11, 18, 22, 59, 52)}})

Copyright (c) 2009-2011 Phil Burrows and CustomInk, released under the MIT license