Connection code

mongo.rb

require 'mongo/retry'
require 'mongo/retry_replica_set_connection'

if ENV['MONGOHQ_REPLICASET_URL']
  # MongoMapper.config = {RAILS_ENV => {'uri' => ENV['MONGOHQ_REPLICASET_URL']}}
  parser = Mongo::URIParser.new(ENV['MONGOHQ_REPLICASET_URL']) #* begin
  MongoMapper.config = {
    RAILS_ENV => {
      'uri' => nil,
      'hosts' => parser.nodes,
      'database' => parser.auths[0]['db_name'],
      'username' => parser.auths[0]['username'],
      'password' => parser.auths[0]['password']
    }
  }

  # parser = Mongo::URIParser.new(MongoMapper.config[RAILS_ENV]['uri']) #* begin
  # mm_env = {}
  # mm_env['uri'] = nil
  # mm_env['hosts'] = parser.nodes
  # mm_env['database'] = parser.auths[0]['db_name']
  # mm_env['username'] = parser.auths[0]['username']
  # mm_env['password'] = parser.auths[0]['password']
  #MongoMapper.connect(mm_env, {:read => :secondary, :auto_refresh => true }) #* end
  MongoMapper.connect(RAILS_ENV, {:read => :secondary, :auto_refresh => true }) # Use this instead of above lines between begin and end and also below lines if/when MongoMapper Rails 2 branch supports multiple hosts/ports separated by commas

  # MongoMapper.connection = Mongo::RetryReplicaSetConnection.new(*(mm_env['hosts'] << {:read => :secondary, :auto_refresh => true }))
  # MongoMapper.database = mm_env['database']
  # MongoMapper.database.authenticate(mm_env['username'], mm_env['password'])
else
  if ENV['MONGOHQ_URL']
    MongoMapper.config = {RAILS_ENV => {'uri' => ENV['MONGOHQ_URL']}}
  else
    MongoMapper.config = {RAILS_ENV => {'uri' => "mongodb://localhost/torsion_#{Rails.env}"}}
  end
  MongoMapper.connect(RAILS_ENV, {:slave_ok => true, :logger => Rails.logger})
end

retry.rb

# encoding: utf-8

## pulled from mongoid

# Provides behaviour for retrying commands on connection failure.
module Mongo::Retry
  # Retries command on connection failures.
  #
  # This is useful when using replica sets. When a primary server wents
  # down and a command is issued, the driver will raise a
  # Mongo::ConnectionFailure. We wait a little bit, because nodes are
  # electing themselves, and then retry the given command.
  #
  # By setting Mongoid.max_retries_on_connection_failure to a value of 0,
  # no attempt will be made, immediately raising connection failure.
  # Otherwise it will attempt to make the specified number of retries
  # and then raising the exception to clients.
  #
  # @example Retry the command.
  # retry_on_connection_failure do
  # collection.send(name, *args)
  # end
  #
  # @since 2.0.0
  def retry_on_connection_failure
    retries = 0
    begin
      yield
    rescue Mongo::ConnectionFailure => ex
      retries += 1
      raise ex if retries > 30 # Config.max_retries_on_connection_failure
      Kernel.sleep(0.5) ## Todo.. modify for event machine
      log_retry retries
      retry
    end
  end

  private

  def log_retry(retry_number)
    puts "A Mongo::ConnectionFailure was raised. Retry attempt ##{retry_number}."
  end
end

retry_replica_set_connection.rb

class Mongo::RetryReplicaSetConnection < Mongo::ReplSetConnection
  ## wraps basic send message calls in catch blocks to auto retry connection
  
  ## per: http://permalink.gmane.org/gmane.comp.db.mongodb.user/25261
  
  # After looking at the Ruby MongoDB driver code it appears that we could
  # handle this transparently in the following methods:
  # Connection::send_message
  # Connection::send_message_with_safe_check
  # Connection::receive_message

  # I put together a new Connection class that is derived from
  # ReplSetConnection to implement this behavior.
  
  ## This is ripped from Mongoid block
  include Mongo::Retry
  
  def send_message(operation, message, opts={})
    retry_on_connection_failure do
      super(operation, message, opts)
    end
  end
  
  def send_message_with_safe_check(operation, message, db_name, log_message=nil, last_error_params=false)
    retry_on_connection_failure do
      super(operation, message, db_name, log_message, last_error_params)
    end
  end
  
  def receive_message(operation, message, log_message=nil, socket=nil, command=false, read=:primary, exhaust=false)
    retry_on_connection_failure do
      super(operation, message, log_message, socket, command, read, exhaust)
    end
  end
end