Verify NAT health with pings before declaring it healthy.

cloudformation_templates/edx-reference-architecture.json

@@ -1799,7 +1799,6 @@
           "        if [ \"$NAT_STATE\" == \"stopped\" ]; then\n",
           "          echo `date` \"-- NAT($PRIMARY_NAT_ID) instance stopped, starting it back up\"\n",
           "          /opt/ec2-api-tools/bin/ec2-start-instances $PRIMARY_NAT_ID -U $EC2_URL\n",
-          "          NAT_HEALTHY=1\n",
           "          sleep $Wait_for_Instance_Start\n",
           "        else\n",
           "          if [ \"$STOPPING_NAT\" == \"0\" ]; then\n",
@@ -1809,10 +1808,14 @@
           "          fi\n",
           "          sleep $Wait_for_Instance_Stop\n",
           "        fi\n",
+          "        unhealthy_nat_pingresult=`ping -c $Num_Pings -W $Ping_Timeout $PRIMARY_NAT_IP| grep time= | wc -l`\n",
+          "        if [ \"$unhealthy_nat_pingresult\" != \"$Num_Pings\" ]; then\n",
+          "          NAT_HEALTHY=1\n",
+          "        fi\n",
           "      done\n",
           "\n",
           "      # Backup nat was healthy so we switched to it.  It is now the primary.\n",
-          "      if [ \"$NAT_HEALTHY\" == \"1\" ]; then\n",
+          "      if [ \"$ROUTE_HEALTHY\" == \"1\" ]; then\n",
           "        TEMP_NAT_ID=$PRIMARY_NAT_ID\n",
           "        TEMP_NAT_IP=$PRIMARY_NAT_IP\n",
           "\n",