diff --git a/lib/synapse.rb b/lib/synapse.rb
index 0b18fd00..4584f7a8 100644
--- a/lib/synapse.rb
+++ b/lib/synapse.rb
@@ -27,6 +27,16 @@ def initialize(opts={})
       # Any exceptions in the watcher threads should wake the main thread so
       # that we can fail fast.
       Thread.abort_on_exception = true
+      if opts['check_interval']
+        @check_interval = opts['check_interval'].to_i
+      else
+        @check_interval = 15
+      end 
+      if opts['max_checks']
+        @max_checks = opts['max_checks'].to_i
+      else
+        @max_checks = 0
+      end 
 
       log.debug "synapse: completed init"
     end
@@ -50,10 +60,14 @@ def run
           log.info "synapse: regenerating haproxy config"
           @haproxy.update_config(@service_watchers)
         else
-          sleep 1
+          sleep @check_interval
         end
 
         loops += 1
+        if @max_checks != 0 and loops > @max_checks
+            log.info "synapse: exiting after #{loops} loops"
+            break
+        end
         log.debug "synapse: still running at #{Time.now}" if (loops % 60) == 0
       end
 
diff --git a/lib/synapse/service_watcher/ec2tag.rb b/lib/synapse/service_watcher/ec2tag.rb
index a3319c26..0d309f7b 100644
--- a/lib/synapse/service_watcher/ec2tag.rb
+++ b/lib/synapse/service_watcher/ec2tag.rb
@@ -1,15 +1,41 @@
 require 'synapse/service_watcher/base'
 require 'aws-sdk'
+require 'ostruct'
+
+InstanceCache = Object.new
+class << InstanceCache
+    def __init__
+        @i_time = Time.now
+        @instances = nil
+        @cacheTimeout = 60
+        @mutex = Mutex.new
+    end
+    def set(instances)
+        @instances = instances
+        @i_time = Time.now
+    end
+    def get()
+        if Time.now - @i_time > (@cacheTimeout + rand(10))
+            @instances = nil
+        end
+        @instances
+    end
+    def get_mutex()
+        @mutex
+    end
+end
 
+InstanceCache.__init__()
 module Synapse
   class EC2Watcher < BaseWatcher
+  
 
     attr_reader :check_interval
 
     def start
       region = @discovery['aws_region'] || ENV['AWS_REGION']
       log.info "Connecting to EC2 region: #{region}"
-
+      AWS.config(:logger => log)
       @ec2 = AWS::EC2.new(
         region:            region,
         access_key_id:     @discovery['aws_access_key_id']     || ENV['AWS_ACCESS_KEY_ID'],
@@ -18,9 +44,10 @@ def start
       @check_interval = @discovery['check_interval'] || 15.0
 
       log.info "synapse: ec2tag watcher looking for instances " +
-        "tagged with #{@discovery['tag_name']}=#{@discovery['tag_value']}"
+        "tagged with #{@discovery['tag_name']}=#{@discovery['tag_value']} #{@discovery['selector']} "
 
       @watcher = Thread.new { watch }
+      instances = instances_with_tags(@discovery['tag_name'], @discovery['tag_value'])
     end
 
     private
@@ -61,11 +88,11 @@ def watch
           current_backends = discover_instances
 
           if last_backends != current_backends
-            log.info "synapse: ec2tag watcher backends have changed."
+            log.info "synapse: ec2tag watcher #{@name} backends have changed."
             last_backends = current_backends
             configure_backends(current_backends)
           else
-            log.info "synapse: ec2tag watcher backends are unchanged."
+            log.info "synapse: ec2tag watcher #{@name} backends are unchanged."
           end
 
           sleep_until_next_check(start)
@@ -86,30 +113,63 @@ def sleep_until_next_check(start_time)
     end
 
     def discover_instances
-      AWS.memoize do
         instances = instances_with_tags(@discovery['tag_name'], @discovery['tag_value'])
-
-        new_backends = []
-
-        # choice of private_dns_name, dns_name, private_ip_address or
-        # ip_address, for now, just stick with the private fields.
-        instances.each do |instance|
-          new_backends << {
-            'name' => instance.private_dns_name,
-            'host' => instance.private_ip_address,
-            'port' => @haproxy['server_port_override'],
-          }
+        if @discovery['selector']
+            instances = eval("instances.select { |i| #{@discovery['selector']}}")
         end
-
-        new_backends
-      end
+        # do not want to update the cached objects
+        inst = []
+        # add server port
+        instances.each { | i |
+            iclone = OpenStruct.new(i.to_h)
+            iclone['port'] = @haproxy['server_port_override'] 
+            inst << iclone
+        }
+        # sort so that the back end are generated in the same way
+        inst.sort_by! { |i| i['name'] }
+        inst
     end
 
     def instances_with_tags(tag_name, tag_value)
-      @ec2.instances
-        .tagged(tag_name)
-        .tagged_values(tag_value)
-        .select { |i| i.status == :running }
+      InstanceCache.get_mutex().synchronize do
+          inst = InstanceCache.get()
+          if inst.nil?
+            tries = 0
+            ntries = 4
+            AWS.memoize do
+                while tries < ntries do
+                    log.info ("AWS API Call for #{tag_name}, #{tag_value}")
+                    begin
+                        instances = @ec2.instances
+                            .tagged(tag_name)
+                            .tagged_values(tag_value)
+                            .select { |i| i.status == :running }
+                        break
+                    rescue Exception => e 
+                        if e.message.include?("Request limit exceeded")
+                            sleeping = rand(6) + 4
+                            log.warn ("#{e.message} retry #{tries} after #{sleeping} sec")
+                            tries += 1
+                            sleep(sleeping)
+                        else
+                            raise e
+                        end
+                    end
+                end
+                inst = []
+                instances.each { | i |
+                    inst_info = OpenStruct.new({'tags' => i.tags.to_h, 
+                                        'host' => i.private_ip_address,
+                                        'name' => i.tags["Name"]})
+                    inst_info.freeze
+                    inst << inst_info
+                }
+                inst.freeze 
+            end
+            InstanceCache.set(inst)
+          end
+          return inst
+      end
     end
 
     def configure_backends(new_backends)