ACE 4710: Find out the response time of a real server

Question

Hi to everyone,
I have a couple of ACE 4710 and I need to find out what is the response time of a real server.
Is there a way for this?
Thank you for any answer!
  giorgio romano

Answer 1

Hi,
Kindly add the following line in your serverfarm configuration:
predictor response syn-to-synack
Suppose your serverfarm looks like this:
serverfarm host AAA_FARM
predictor response syn-to-synack
probe HTTP_PROBE
probe TCP9001_PROBE
rserver SC106
inservice
rserver SC107
inservice
rserver SC108
inservice
rserver SC109
inservice
rserver SC110
inservice
rserver SC111
inservice
rserver SC112
inservice
rserver SC113
inservice
rserver SC114
inservice
rserver SC120
inservice
rserver SC131
inservice
And then use the following command to see the average response time from your rserver as follows:
ACE1/prod# show serverfarm AAA_FARM detail
serverfarm     : AAA_FARM, type: HOST
total rservers : 11
active rservers: 11
description    : ServerFarm AAA
state          : ACTIVE
predictor      : RESPONSE
method            : syn-to-synack
samples           : 8
failaction     : -
back-inservice    : 0
partial-threshold : 0
num times failover       : 0
num times back inservice : 0
total conn-dropcount : 0
Probe(s) :
HTTP_PROBE,  type = HTTP
TCP9001_PROBE,  type = TCP
----------connections-----------
real                  weight state        current    total      failures
---+---------------------+------+------------+----------+----------+---------
rserver: SC106
x.x.x.x.:0        8      OPERATIONAL  2          1125       0
max-conns            : 4000000   , out-of-rotation count : 0
min-conns            : 4000000
conn-rate-limit      : -         , out-of-rotation count : -
bandwidth-rate-limit : -         , out-of-rotation count : -
retcode out-of-rotation count : -
load value           : 0
average response time (usecs) : 81   ----> thats what you might be looking for
From other day :
rserver: SC114
x.x.x.x:0        8      OPERATIONAL  70         10903      2
max-conns            : 4000000   , out-of-rotation count : 0
min-conns            : 4000000
conn-rate-limit      : -         , out-of-rotation count : -
bandwidth-rate-limit : -         , out-of-rotation count : -
retcode out-of-rotation count : -
load value           : 0
         average response time (usecs) : 1334                       ----> thats what you might be looking for
For Serverfarm BBB_FARM
serverfarm     : BBB_FARM, type: HOST
total rservers : 1
active rservers: 1
description    : ServerFarm BBB
state          : ACTIVE
predictor      : RESPONSE
method            : syn-to-synack
samples           : 8
failaction     : -
back-inservice    : 0
partial-threshold : 0
num times failover       : 1
num times back inservice : 1
total conn-dropcount : 0
Probe(s) :
----------connections-----------
real                  weight state        current    total      failures
---+---------------------+------+------------+----------+----------+---------
rserver: SC208
x.x.x.x:0        8      OPERATIONAL  0          0          0
max-conns            : 4000000   , out-of-rotation count : 0
min-conns            : 4000000
conn-rate-limit      : -         , out-of-rotation count : -
bandwidth-rate-limit : -         , out-of-rotation count : -
retcode out-of-rotation count : -
load value           : 0
         average response time (usecs) : 0   ----> thats what you might be looking for
Use more detials for response predictor:
http://www.cisco.com/en/US/docs/app_ntwk_services/data_center_app_services/ace_appliances/vA3_1_0/configuration/slb/guide/rsfarms.html#wp1068831
Configuring the Application Response Predictor
To instruct the ACE to select the server with the lowest average response time for the specified response-time measurement based on the current connection count and server weight (if configured), use the predictor response command in server farm host or redirect configuration mode. This predictor is considered adaptive because the ACE continuously provides feedback to the load-balancing algorithm based on the behavior of the real server.
To select the appropriate server, the ACE measures the absolute response time for each server in the server farm and averages the result over a specified number of samples (if configured). With the default weight connection option configured, the ACE also takes into account the server's average response time and current connection count. This calculation results in a connection distribution that is proportional to the average response time of the server.
The syntax of this command is as follows:
predictor response {app-req-to-resp | syn-to-close | syn-to-synack}[samples number]
The keywords and arguments are as follows:
•app-request-to-resp—Measures the response time from when the ACE sends an HTTP request to a server to the time that the ACE receives a response from the server for that request.
•syn-to-close—Measures the response time from when the ACE sends a TCP SYN to a server to the time that the ACE receives a CLOSE from the server.
•syn-to-synack—Measures the response time from when the ACE sends a TCP SYN to a server to the time that the ACE receives the SYN-ACK from the server.
•samples number—(Optional) Specifies the number of samples over which you want to average the results of the response time measurement. Enter an integer from 1 to 16 in powers of 2. Valid values are 1, 2, 4, 8, and 16. The default is 8.
For example, to configure the response predictor to load balance a request based on the response time from when the ACE sends an HTTP request to a server to when the ACE receives a response back from the server and average the results over four samples, enter:
host1/Admin(config)# serverfarm SFARM1
host1/Admin(config-sfarm-host)# predictor response app-req-to-resp
samples 4
To reset the predictor method to the default of round-robin, enter:
host1/Admin(config-sfarm-host)# no predictor
To configure an additional parameter to take into account the current connection count of the servers in a server farm, use the weight connection command in server farm host predictor configuration mode. By default, this command is enabled. The syntax of this command is as follows:
weight connection
For example, enter:
host1/Admin(config)# serverfarm SF1
host1/Admin(config-sfarm-host)# predictor response app-request-to-resp
samples 4
host1/Admin(config-sfarm-host-predictor)# weight connection
To remove the current connection count from the calculation of the average server response time, enter:
host1/Admin(config-sfarm-host-predictor)# no weight connection
You can use threshold milliseconds parameter which is optional Specifies the required minimum average response time for a server. If the server response time is greater than the specified threshold value, the ACE removes the server from the load-balancing decision process (takes the server out of service).
Enter an integer from 1 to 300000 milliseconds (5 minutes). The default is no threshold (servers are not taken out of service).
In case if you have measures the response time from  when the ACE sends a TCP SYN to a server to the time that the ACE receives a CLOSE from the server  use syn-to-close      (already discussed previously)
If you have to measures the response time from when the ACE sends a TCP SYN to a server to the time that the ACE receives the SYN-ACK from the server use syn-to-synack   (already discussed previously)
SAMPLES parameter is optional and  specifies the number of samples that you want to average from the results of the response time measurement and response time is used to select the server with the lowest response time for the requested response-time measurement. If you do not specify a response-time measurement method, the ACE uses the HTTP app-req-to-response method.
Whenever a server's load reaches zero, by default, the ACE uses the autoadjust feature to assign a maximum load value of 16000 to that server to prevent it from being flooded with new incoming connections. The ACE periodically adjusts this load value based on feedback from the server's SNMP probe and other configured options.
Using the least-loaded predictor with the configured server weight and the current connection count option enabled, the ACE calculates the final load of a real server as follows:
final load = weighted load × static weight × current connection count
where:
•weighted load is the load reported by the SNMP probe
•static weight is the configured weight of the real server
•current connection count is the total number of active connections to the real server
The ACE recalculates the final load whenever the connection count changes, provided that the (config-sfarm-host-predictor) weight connection command is configured. If the (config-sfarm-host-predictor) weight connection command is not configured, the ACE updates the final load when the next load update arrives from the SNMP probe.
If two servers have the same lowest load (either zero or nonzero), the ACE load balances the connections between the two servers in a round-robin manner.
HTH
Plz rate if u find it useful.
Sachin