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Leastconns predictor and multiple serverfarms?

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A.Swinnen
Level 1
Level 1

‎10-28-2010 04:12 AM

Hi,

I have some real servers that are configured into multiple serverfarms. If I configure the pedictor of a serverfarm as leastconns, does it take into account only the connections within this serverfarm to a particular real server or does it take into account all connections towards a particular real server over the different serverfarms?

For example:

serverfarm host SF1

predictor roundrobin

rserver RS1

  inservice

rserver RS2

  inservice

serverfarm host SF2

predictor leastconns

rserver RS1

  inservice

rserver RS2

  inservice

Let's assume the following situation:

SF1:

     RS1: 100 connections active

     RS2: 120 connections active

SF2:

     RS1: 60 connections active

     RS2: 50 connections active

What will then happen for a new connection on SF2:

     a. RS1 is chosen, because (100 + 60) < (120 + 50)

     b. RS2 is chosen, because 50 < 60

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Accepted Solutions

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yushimaz
Cisco Employee
Cisco Employee

‎10-28-2010 10:58 PM

>     b. RS2 is chosen, because 50 < 60

The answer is b as a matter of logic since ACE handles predictor each serverfarm, not real server.

This means connection counts in SF1 don't affect the predictor for SF2.

FYI, The following is my test result.

### Test 1 (RS1 and RS2 in SF2 have same connection.)

ACE/Admin# sh rserver

rserver              : sv1, type: HOST

state                : OPERATIONAL (verified by arp response)

---------------------------------

                                                ----------connections-----------

       real                  weight state        current    total

   ---+---------------------+------+------------+----------+--------------------

   serverfarm: sf1

       192.168.72.1:0        8      OPERATIONAL  10         162

   serverfarm: sf2

       192.168.72.1:0        8      OPERATIONAL  18         25 <<==

rserver              : sv2, type: HOST

state                : OPERATIONAL (verified by arp response)

---------------------------------

                                                ----------connections-----------

       real                  weight state        current    total

   ---+---------------------+------+------------+----------+--------------------

   serverfarm: sf1

       192.168.72.2:0        8      OPERATIONAL  20         164

   serverfarm: sf2

       192.168.72.2:0        8      OPERATIONAL  18         18  <<==

ACE/Admin#

## After 4 connections were established, both RS1 and RS2 in SF2 were counted.

ACE/Admin# sh rserver

rserver              : sv1, type: HOST

state                : OPERATIONAL (verified by arp response)

---------------------------------

                                                ----------connections-----------

       real                  weight state        current    total

   ---+---------------------+------+------------+----------+--------------------

   serverfarm: sf1

       192.168.72.1:0        8      OPERATIONAL  10         162

   serverfarm: sf2

       192.168.72.1:0        8      OPERATIONAL  20         27  <<== 18 conns -> 20 conns

rserver              : sv2, type: HOST

state                : OPERATIONAL (verified by arp response)

---------------------------------

                                                ----------connections-----------

       real                  weight state        current    total

   ---+---------------------+------+------------+----------+--------------------

   serverfarm: sf1

       192.168.72.2:0        8      OPERATIONAL  20         164

   serverfarm: sf2

       192.168.72.2:0        8      OPERATIONAL  20         20  <<== 18 conns -> 20 conns

ACE/Admin#

### Test 2 (RS1 in SF2 > RS2 in SF2, sum of SF1 = sum of SF2)

ACE/Admin# sh rserver
rserver              : sv1, type: HOST
state                : OPERATIONAL (verified by arp response)
---------------------------------
                                                ----------connections-----------
       real                  weight state        current    total
   ---+---------------------+------+------------+----------+--------------------
   serverfarm: sf1
       192.168.72.1:0        8      OPERATIONAL  10         162
   serverfarm: sf2
       192.168.72.1:0        8      OPERATIONAL  22         32  <<==
rserver              : sv2, type: HOST
state                : OPERATIONAL (verified by arp response)
---------------------------------
                                                ----------connections-----------
       real                  weight state        current    total
   ---+---------------------+------+------------+----------+--------------------
   serverfarm: sf1
       192.168.72.2:0        8      OPERATIONAL  20         164
   serverfarm: sf2
       192.168.72.2:0        8      OPERATIONAL  12         28  <<==
ACE/Admin#

## When 8 connections were established, only RS2 in SF2 were counted.

ACE/Admin# sh rserver
rserver              : sv1, type: HOST
state                : OPERATIONAL (verified by arp response)
---------------------------------
                                                ----------connections-----------
       real                  weight state        current    total
   ---+---------------------+------+------------+----------+--------------------
   serverfarm: sf1
       192.168.72.1:0        8      OPERATIONAL  10         162
   serverfarm: sf2
       192.168.72.1:0        8      OPERATIONAL  22         32  <<==
rserver              : sv2, type: HOST
state                : OPERATIONAL (verified by arp response)
---------------------------------
                                                ----------connections-----------
       real                  weight state        current    total
   ---+---------------------+------+------------+----------+--------------------
   serverfarm: sf1
       192.168.72.2:0        8      OPERATIONAL  20         164
   serverfarm: sf2
       192.168.72.2:0        8      OPERATIONAL  20         36  <<== 12 conns -> 20 conns
ACE/Admin#
Regards,

Yuji

View solution in original post

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2 Replies 2

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yushimaz
Cisco Employee
Cisco Employee

‎10-28-2010 10:58 PM

>     b. RS2 is chosen, because 50 < 60

The answer is b as a matter of logic since ACE handles predictor each serverfarm, not real server.

This means connection counts in SF1 don't affect the predictor for SF2.

FYI, The following is my test result.

### Test 1 (RS1 and RS2 in SF2 have same connection.)

ACE/Admin# sh rserver

rserver              : sv1, type: HOST

state                : OPERATIONAL (verified by arp response)

---------------------------------

                                                ----------connections-----------

       real                  weight state        current    total

   ---+---------------------+------+------------+----------+--------------------

   serverfarm: sf1

       192.168.72.1:0        8      OPERATIONAL  10         162

   serverfarm: sf2

       192.168.72.1:0        8      OPERATIONAL  18         25 <<==

rserver              : sv2, type: HOST

state                : OPERATIONAL (verified by arp response)

---------------------------------

                                                ----------connections-----------

       real                  weight state        current    total

   ---+---------------------+------+------------+----------+--------------------

   serverfarm: sf1

       192.168.72.2:0        8      OPERATIONAL  20         164

   serverfarm: sf2

       192.168.72.2:0        8      OPERATIONAL  18         18  <<==

ACE/Admin#

## After 4 connections were established, both RS1 and RS2 in SF2 were counted.

ACE/Admin# sh rserver

rserver              : sv1, type: HOST

state                : OPERATIONAL (verified by arp response)

---------------------------------

                                                ----------connections-----------

       real                  weight state        current    total

   ---+---------------------+------+------------+----------+--------------------

   serverfarm: sf1

       192.168.72.1:0        8      OPERATIONAL  10         162

   serverfarm: sf2

       192.168.72.1:0        8      OPERATIONAL  20         27  <<== 18 conns -> 20 conns

rserver              : sv2, type: HOST

state                : OPERATIONAL (verified by arp response)

---------------------------------

                                                ----------connections-----------

       real                  weight state        current    total

   ---+---------------------+------+------------+----------+--------------------

   serverfarm: sf1

       192.168.72.2:0        8      OPERATIONAL  20         164

   serverfarm: sf2

       192.168.72.2:0        8      OPERATIONAL  20         20  <<== 18 conns -> 20 conns

ACE/Admin#

### Test 2 (RS1 in SF2 > RS2 in SF2, sum of SF1 = sum of SF2)

ACE/Admin# sh rserver
rserver              : sv1, type: HOST
state                : OPERATIONAL (verified by arp response)
---------------------------------
                                                ----------connections-----------
       real                  weight state        current    total
   ---+---------------------+------+------------+----------+--------------------
   serverfarm: sf1
       192.168.72.1:0        8      OPERATIONAL  10         162
   serverfarm: sf2
       192.168.72.1:0        8      OPERATIONAL  22         32  <<==
rserver              : sv2, type: HOST
state                : OPERATIONAL (verified by arp response)
---------------------------------
                                                ----------connections-----------
       real                  weight state        current    total
   ---+---------------------+------+------------+----------+--------------------
   serverfarm: sf1
       192.168.72.2:0        8      OPERATIONAL  20         164
   serverfarm: sf2
       192.168.72.2:0        8      OPERATIONAL  12         28  <<==
ACE/Admin#

## When 8 connections were established, only RS2 in SF2 were counted.

ACE/Admin# sh rserver
rserver              : sv1, type: HOST
state                : OPERATIONAL (verified by arp response)
---------------------------------
                                                ----------connections-----------
       real                  weight state        current    total
   ---+---------------------+------+------------+----------+--------------------
   serverfarm: sf1
       192.168.72.1:0        8      OPERATIONAL  10         162
   serverfarm: sf2
       192.168.72.1:0        8      OPERATIONAL  22         32  <<==
rserver              : sv2, type: HOST
state                : OPERATIONAL (verified by arp response)
---------------------------------
                                                ----------connections-----------
       real                  weight state        current    total
   ---+---------------------+------+------------+----------+--------------------
   serverfarm: sf1
       192.168.72.2:0        8      OPERATIONAL  20         164
   serverfarm: sf2
       192.168.72.2:0        8      OPERATIONAL  20         36  <<== 12 conns -> 20 conns
ACE/Admin#
Regards,

Yuji

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Go to solution
A.Swinnen
Level 1
Level 1
In response to yushimaz

‎10-29-2010 01:29 AM

Hi,

This makes sense and is also what I expected. However it is not completely what I desired for a particular application

Kind Regards,

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