auto-failover ReplicaSet config for MongoMapper, by way of ruby driver

gistfile1.txt

replica_sets = mm_env['replica_sets']  # node1:port&node2:port

rs_list = replica_sets.split("&").map {|rs| host,port = rs.split(":"); [host,port.to_i] }
    
MongoMapper.connection = Mongo::RetryReplicaSetConnection.new(*(rs_list << {:read_secondary => true, :auto_refresh  => true }))

MongoMapper.database = mm_env['database']
MongoMapper.database.authenticate(mm_env['username'], mm_env['password']) 

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
    rescue Mongo::OperationFailure => ex
      if ex.message =~ /not master/
        retries += 1
        raise ex if retries > 30
        Kernel.sleep(0.5)
        log_retry retries
        retry
      else
        raise ex
      end
    end
  end

  private

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

retry_replica_set_connetion.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)
    retry_on_connection_failure do
      super(operation, message, log_message, socket, command)
    end
  end
   
end