RSolr with default headers for websolr preferential routing to master or slave

rsolr_with_default_headers.rb

# Websolr can use HTTP headers to control authorization and request routing.
# This class injects a connection wrapper into Sunspot to set default headers
# on every request.
#
# Interesting values for X-Websolr-Routing:
#  - prefer-master (route serches to master, for real-time search; cpu expensive; current default)
#  - prefer-random (distribute searches evenly; for high-volume of searches relative to updates)
#  - prefer-replica (isolate search requests from updates; for high-volumes of one type of traffic negatively impacting the other)
#

class RSolrWithDefaultHeaders
  attr_accessor :default_headers

  def initialize(default_headers = {})
    self.default_headers = default_headers
  end

  def connect(opts = {})
    RSolr::Client.new(ConnectionWithDefaultHeaders.new(default_headers), opts)
  end

  class ConnectionWithDefaultHeaders < ::RSolr::Connection
    attr_accessor :default_headers

    def initialize(default_headers)
      self.default_headers = default_headers
    end

    def setup_raw_request_with_default_headers(request_context={})
      request_context[:headers] = request_context[:headers].merge(default_headers)
      setup_raw_request_without_default_headers(request_context)
    end

    alias_method_chain :setup_raw_request, :default_headers
  end
end

Sunspot::Session.connection_class = RSolrWithDefaultHeaders.new({
  'X-Websolr-Routing' => 'prefer-replica'
})