handle excon errors in herou scaler

lib/autoscaler/heroku_scaler.rb

@@ -26,7 +26,7 @@ def workers
       if known?
         @workers
       else
-        know client.get_ps(app).body.count {|ps| ps['process'].match /#{type}\.\d?/ }
+        know heroku_get_workers
       end
     end
 
@@ -35,11 +35,23 @@ def workers
     def workers=(n)
       if n != @workers || !known?
         p "Scaling #{type} to #{n}"
-        client.post_ps_scale(app, type, n)
+        heroku_set_workers(n)
         know n
       end
     end
 
+    # Callable object which responds to exceptions during api calls
+    #
+    # @example
+    #   heroku.exception_handler = lambda {|exception| MyApp.logger.error(exception)}
+    #   heroku.exception_handler = lambda {|exception| raise}
+    #   # default
+    #   lambda {|exception|
+    #     p exception
+    #     puts exception.backtrace
+    #   }
+    attr_writer :exception_handler
+
     private
     attr_reader :client
 
@@ -51,5 +63,25 @@ def know(n)
     def known?
       Time.now < @known
     end
+
+    def heroku_get_workers
+      client.get_ps(app).body.count {|ps| ps['process'].match /#{type}\.\d?/ }
+    rescue Excon::Errors::Error => e
+      exception_handler.call(e)
+      @workers
+    end
+
+    def heroku_set_workers(n)
+      client.post_ps_scale(app, type, n)
+    rescue Excon::Errors::Error => e
+      exception_handler.call(e)
+    end
+
+    def exception_handler
+      @exception_handler ||= lambda {|exception|
+        p exception
+        puts exception.backtrace
+      }
+    end
   end
 end

spec/autoscaler/heroku_scaler_spec.rb

@@ -17,4 +17,27 @@
 
     its(:workers) {should == 1}
   end
+
+  describe 'exception handling', :focus => true do
+    before do
+      def client.client
+        raise Excon::Errors::SocketError.new(Exception.new('oops'))
+      end
+    end
+
+    describe "default handler" do
+      it {expect{client.workers}.to_not raise_error}
+      it {client.workers.should == 0}
+      it {expect{client.workers = 1}.to_not raise_error}
+    end
+
+    describe "custom handler" do
+      before do
+        @caught = false
+        client.exception_handler = lambda {|exception| @caught = true}
+      end
+
+      it {client.workers; @caught.should be_true}
+    end
+  end
 end