Recently
worked on Load Monitors and it was quite tricky as there is no proper
explanation for same. Sharing my knowledge based on that
Custom
Load Monitors:-
When you
have a scenario where you need to do load balancing based on the Load then we
go for the CUSTOMLOAD Method and Load monitors.
Load
monitors use SNMP polled OIDs to calculate load. The load monitor uses the IP
address of the service to which it is bound (the destination IP address) for
polling. It sends an SNMP query to the service, specifying the OID for a
metric. The metrics can be CPU, memory, or number of server connections. The
server responds to the query with a metric value. The metric value in the
response is compared with the threshold value. The NetScaler appliance
considers the service for load balancing only if the metric is less than the
threshold value. The service with the lowest load value is considered first.
Use Case
Scenario:- GSLB
load balancing method doesn’t understand the Actual load on the Server but the
load on the loadbalancer. So if you need to do a GSLB loadbalancing based on
the Load on the Server then you go for this method.
Another Scenario would be when you want to load balance based on cpu of the server or Memory load on the server or traffic load. i.e any value which can be fetched via SNMP.
Note:-
The backend server should be SNMP compatible so that Netscaler can fetch the value using SNMP
Lab
Method:-
LB on the
Netscaler
Service 1
is the NS1
Service 2
is the NS2
Method is
based on the number of client connection on the NS1 and NS2
Configuration:-
First need
to create a Metric Table for the SNMP, Here I am using the Inbuilt Netscaler
Metric Table
Then Create
A Load Monitor and give the destination ip as the IP of the Server
Under the
Special Parameters select the Metric Table and provide the type ( Here I am
using the client connection) and Give the Threshold ( I have given 50 here).
SNMP
Community name should be based on the name you are using for SNMP. Here I am
using public so my server SNMP community name should also be “public”
Similarly
Create the other Load Monitor for Second Server
Now We need
to create the Services for same
Create the
first service as NS1 and bind the Load Monitor 1
And for
Second Service NS2 bind the Load Monitor 2
Now on the
LB Vserver bind the 2 services
And select
the Method as CUSTOMLOAD
This all
scenario works based on the SNMP Value received. This should be an Integer
Value. So make sure the Backend server are giving proper response for the SNMP
Query.
FLOW and
Design :-
Initially
when you will configure this method the present method you will notice will be
Round Robin
> sh lb
vserver lb
lb (10.104.23.72:80) - HTTP Type: ADDRESS
State: UP
Last state change was at Sat Apr 4 10:36:35 2015
Time since last state change: 0 days, 00:14:25.870
Effective State: UP
Client Idle Timeout: 180 sec
Down state flush: ENABLED
Disable Primary Vserver On Down : DISABLED
Appflow logging: ENABLED
Port Rewrite : DISABLED
No. of Bound Services : 2 (Total) 2
(Active)
Configured Method: CUSTOMLOAD
Current Method: Round
Robin, Reason: A new service is bound
Mode: IP
Persistence: NONE
Vserver IP and Port insertion: OFF
Push: DISABLED Push VServer:
Push Multi Clients: NO
Push Label Rule: none
L2Conn: OFF
Skip Persistency: None
IcmpResponse: PASSIVE
New Service Startup Request Rate: 0 PER_SECOND, Increment Interval: 0
TD: 0
Mac mode Retain Vlan: DISABLED
DBS_LB: DISABLED
DNS64 Synth: DISABLED Bypass AAAA: NO
1) NS1
(10.104.23.131: 80) - HTTP State: UP Weight: 1
2) NS2 (10.104.40.43:
80) - HTTP State: UP Weight: 1
In stat lb
connection you can notice the number of Hits to the site and connection
> stat
lb vserver lb
Virtual
Server Summary
vsvrIP
port Protocol
State Health actSvcs
lb
10.104.23.72
80
HTTP
UP 100
2
inactSvcs
lb
0
Virtual
Server Statistics
Rate (/s)
Total
Vserver
hits
0
0
Requests
0
0
Responses
0
0
Request
bytes
0
0
Response
bytes
0
0
Total
Packets
rcvd
0
0
Total
Packets
sent
0
0
Current
client connections
--
25
Current
Client Est
connections
--
25
Current
server
connections
--
0
Requests in
surge
queue
--
0
Requests in
vserver's
surgeQ
--
0
Requests in
service's
surgeQs
--
0
Spill Over
Threshold
--
0
Spill Over
Hits
--
0
Labeled
Connection
--
0
Push
Labeled
Connection
-- 0
Deferred
Request
0
0
Invalid
Request/Response
--
0
Invalid
Request/Response
Dropped
--
0
Bound
Service(s) Summary
IP port
Type State
Hits Hits/s
NS1
10.104.23.131
80
HTTP UP
0 0/s
NS2
10.104.40.43
80
HTTP UP
0 0/s
Req
Req/s Rsp Rsp/s Throughp
ClntConn SurgeQ
NS1
0 0/s
0 0/s 0
0 0
NS2
0 0/s
0 0/s 0
0 0
SvrConn ReuseP MaxConn ActvTran
SvrTTFB Load
NS1
9
0 0
0
0 42
NS2
9
0
0 0
0 82
In the
Wireshark You can see the number of Connections based on SNMP to the Service
Initial
Method will show Round Robin unless the Server receives enough number of
Request. The CustomLoad method will start when the number of Hits exceeds the
Threshold value ( 50) for both the value.
I do see
that in my lab the number of Hits Reached 102/103 but still the Method was
Round Robin, So I suspect it takes some number of request which should be
greater then threshold when it triggers the Custom Load.
> stat
lb vserver lb
Bound
Service(s) Summary
IP port
Type State
Hits Hits/s
NS1
10.104.23.131
80
HTTP
UP 138 5/s
NS2
10.104.40.43 80
HTTP
UP 137 5/s
Done
> sh lb
vserver lb
lb (10.104.23.72:80) - HTTP Type: ADDRESS
State: UP
Last state change was at Sat Apr 4 10:36:35 2015
Time since last state change: 0 days, 00:15:17.800
Effective State: UP
Client Idle Timeout: 180 sec
Down state flush: ENABLED
Disable Primary Vserver On Down : DISABLED
Appflow logging: ENABLED
Port Rewrite : DISABLED
No. of Bound Services : 2 (Total) 2
(Active)
Configured Method: CUSTOMLOAD
Current Method: Round
Robin, Reason: A new service is bound
Mode: IP
Persistence: NONE
I do see
when the Request reached enough Numbers like 265 then the CUSTOM Load was
Triggered
> stat
lb vserver lb
Virtual
Server Summary
vsvrIP port
Protocol State
Health actSvcs
lb
10.104.23.72
80
HTTP
UP 100
2
inactSvcs
lb
0
Virtual
Server Statistics
Rate (/s)
Total
Bound
Service(s) Summary
IP port
Type State
Hits Hits/s
NS1
10.104.23.131
80
HTTP
UP 265 10/s
NS2
10.104.40.43
80
HTTP
UP 150 0/s
> sh lb
vserver lb
lb (10.104.23.72:80) - HTTP Type: ADDRESS
State: UP
Last state change was at Sat Apr 4 10:36:35 2015
Time since last state change: 0 days, 00:15:39.240
Effective State: UP
Client Idle Timeout: 180 sec
Down state flush: ENABLED
Disable Primary Vserver On Down : DISABLED
Appflow logging: ENABLED
Port Rewrite : DISABLED
No. of Bound Services : 2 (Total) 2
(Active)
Configured Method:
CUSTOMLOAD
Mode: IP
Persistence: NONE
Vserver IP and Port insertion: OFF
Push: DISABLED Push VServer:
Push Multi Clients: NO
Push Label Rule: none
L2Conn: OFF
Skip Persistency: None
IcmpResponse: PASSIVE
New Service Startup Request Rate: 0 PER_SECOND, Increment Interval: 0
TD: 0
Mac mode Retain Vlan: DISABLED
DBS_LB: DISABLED
DNS64 Synth: DISABLED Bypass AAAA: NO
1) NS1
(10.104.23.131: 80) - HTTP State: UP Weight: 1
2) NS2
(10.104.40.43: 80) - HTTP State: UP Weight: 1
Now the
Netscaler Will See the SNMP Response Returned by both the Service and the load
will be shared based on the low value
As we
notice that NS1 service is giving a response as 30 and NS2 is giving a response
as 23. So More load will be given to NS2. We can confirm that in stat lb
> stat
lb vserver lb
Virtual
Server Summary
vsvrIP
port Protocol
State Health actSvcs
lb
10.104.23.72
80 HTTP
UP 100
2
inactSvcs
lb
0
Virtual
Server Statistics
Rate (/s)
Total
Vserver
hits
52
1050
Requests
52
1050
Responses
52
1048
Request
bytes
5689
115060
Response
bytes
897924
18392716
Total
Packets
rcvd
485
9840
Total
Packets
sent
798
16264
Current
client
connections
--
7
Current
Client Est
connections
--
7
Current
server
connections
--
2
Requests in
surge
queue
--
0
Requests in
vserver's surgeQ
--
0
Requests in
service's
surgeQs
--
0
Spill Over
Threshold
--
0
Spill Over
Hits
--
0
Labeled
Connection
--
0
Push
Labeled
Connection
--
0
Deferred
Request
0
0
Invalid
Request/Response
--
0
Invalid
Request/Response
Dropped
--
0
Bound
Service(s) Summary
IP port
Type
State Hits Hits/s
NS1
10.104.23.131
80
HTTP
UP 850 45/s
NS2
10.104.40.43
80
HTTP
UP 200 7/s
Req
Req/s Rsp Rsp/s Throughp
ClntConn SurgeQ
NS1
850 45/s
849 45/s
6 1
0
NS2
200 7/s
199 7/s
1
1 0
SvrConn ReuseP MaxConn ActvTran
SvrTTFB Load
NS1
4
3
0 1
18 54
NS2
8
1
0 1
59 102
Now this
will continue untill we are not reaching the Threshold of 50 provided in the LB
Monitor
Now if any
of the Backend Server reaches the Threshold of 50 and reply with a Value of
more than 50 then LB will Skip that service.
As we see
if there are more connection on the server then we receive following Response
from the Backend Servers on SNMP which is exceeding the Threshold we have
configured.
Then the
Netscaler will skip the service
> sh lb
vserver lb
lb (10.104.23.72:80) - HTTP Type: ADDRESS
State: UP
Last state change was at Sat Apr 4 10:36:35 2015
Time since last state change: 0 days, 00:17:25.590
Effective State: UP
Client Idle Timeout: 180 sec
Down state flush: ENABLED
Disable Primary Vserver On Down : DISABLED
Appflow logging: ENABLED
Port Rewrite : DISABLED
No. of Bound Services : 2 (Total) 2
(Active)
Configured Method: CUSTOMLOAD
Mode: IP
Persistence: NONE
Vserver IP and Port insertion: OFF
Push: DISABLED Push VServer:
Push Multi Clients: NO
Push Label Rule: none
L2Conn: OFF
Skip Persistency: None
IcmpResponse: PASSIVE
New Service Startup Request Rate: 0 PER_SECOND, Increment Interval: 0
TD: 0
Mac mode Retain Vlan: DISABLED
DBS_LB: DISABLED
DNS64 Synth: DISABLED Bypass AAAA: NO
1) NS1 (10.104.23.131: 80) - HTTP State:
UP Weight: 1
Warning: Service will be skipped in LB as it has reached threshold
2) NS2
(10.104.40.43: 80) - HTTP State: UP Weight: 1
Warning: Service will be
skipped in LB as it has reached threshold
1)
Policy : appfw Priority:100 GotoPriority Expression:
END
Done
