Added the "roundrobin" strategy for the BalancingProxy

examples/balancing.rb

@@ -34,6 +34,9 @@ def self.select(strategy = :balanced)
       case @strategy
         when :balanced
           backend = new list.sort { |a,b| a.values <=> b.values }.first.keys.first
+        when :roundrobin
+          @pool = list.clone if @pool.nil? || @pool.empty?
+          backend = new @pool.shift.keys.first
         when :random
           backend = new list[ rand(list.size-1) ].keys.first
         else

spec/proxy_spec.rb

@@ -173,7 +173,7 @@ def failed
 
   before(:each) do
     class BalancingProxy::Backend
-      @list = nil
+      @list = nil; @pool = nil
     end
   end
 
@@ -206,6 +206,25 @@ def self.list
 
   end
 
+  context "when using the 'roundrobin' strategy" do
+    it "should select backends in rotating order" do
+      class BalancingProxy::Backend
+        def self.list
+          @list ||= [
+            {"http://127.0.0.1:3000" => 0},
+            {"http://127.0.0.2:3000" => 0},
+            {"http://127.0.0.3:3000" => 0}
+          ]
+        end
+      end
+
+      BalancingProxy::Backend.select(:roundrobin).host.should == '127.0.0.1'
+      BalancingProxy::Backend.select(:roundrobin).host.should == '127.0.0.2'
+      BalancingProxy::Backend.select(:roundrobin).host.should == '127.0.0.3'
+      BalancingProxy::Backend.select(:roundrobin).host.should == '127.0.0.1'
+    end
+  end
+
   context "when using the 'balanced' strategy" do
 
     it "should select the first backend when all backends have the same load" do