Question on ASP.NET SQL Server Session clustering with external load balancer (BIG F5)

Satheeshkumar Thirugnanam 1 Reputation point
2022-05-10T21:06:47.303+00:00

Our Current Setup
We have 4 IIS Servers where our ASP .NET application has been deployed.
In IIS, the session state is configured as SQL Server (External )
All the 4 IIS servers are configured as active pool members in the BIG F5 load balancer
On a normal scenario/traffic, we could see almost equal number of connections established across all the 4 members of the big F5 pool.

Problem Statement
If there is an issue with one of the IIS servers, we disable that server from the F5 pool. Even after disabling we don't see the connections are going down in the F5 pool.
Now we will restart that IIS server and the strange thing we have noticed during the restart is: the TCP active connections in the other active servers in the big F5 is drastically increasing (nearly 10 times) and at the same time the CPUs reached out to 100% in all those 3 active servers.
We would need your help to find out what would have caused this issue or if anyone else come across this scenario before.

.NET Framework Version: 4.6
IIS Version: 8.5.9600.16384
SQL Server Version: MS SQL 2016 SP2

Internet Information Services
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4 answers

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  1. Bruce (SqlWork.com) 61,181 Reputation points
    2022-05-10T22:41:29.767+00:00

    which load balancing algorithm are you using? is the IIS server up and running before adding to the pool? are you using server affinity?


  2. Satheeshkumar Thirugnanam 1 Reputation point
    2022-05-11T00:39:21.343+00:00

    Which load balancing algorithm are you using? Round robin
    Is the IIS server up and running before adding to the pool? Yes
    Are you using server affinity? SQL Server session management


  3. Satheeshkumar Thirugnanam 1 Reputation point
    2022-05-12T15:57:42.443+00:00

    Hi Bruce, i have responded to your questions. Do you have further updates

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  4. Satheeshkumar Thirugnanam 1 Reputation point
    2022-05-12T21:28:32.697+00:00

    Yes, Its the IIS server which we are adding back into pool. There are no server affinity setup on the F5 side

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