Load balancing MSSQL

NetScaler is the only certified load balancer that can load balance the MySQL and MSSQL services. It can be quite complex and there are many requirements that need to be in place in order to set up a proper load-balanced SQL server.

Let us go through how to set up a load-balanced Microsoft SQL Server running on 2008 R2. Now, it is important to remember that using load balancing between the end clients and SQL Server requires that the databases on the SQL server are synchronized. This is to ensure that the content that the user is requesting is available on all the backend servers. Microsoft SQL Server supports different types of availability solutions, such as replication. You can read more about it at http://technet.microsoft.com/en-us/library/ms152565(v=sql.105).aspx. Using transactional replication is recommended, as this replicates changes to different SQL servers as they occur.

As of now, the load balancing solution for MSSQL, also called DataStream, supports only certain versions of SQL Server. They can be viewed at http://support.citrix.com/proddocs/topic/netscaler-traffic-management-10-map/ns-dbproxy-reference-protocol-con.html. Also, only certain authentication methods are supported. As of now, only SQL authentication is supported for MSSQL.

The steps to set up load balancing are as follows:

1. We need to add the backend SQL servers to the list of servers.
2. Next, we need to create a custom monitor that we are going to use against the backend servers.
3. Before we create the monitor, we can create a custom database within SQL Server that NetScaler can query.
4. Open Object Explorer in the SQL Management Studio, and right-click on the Database folder. Then, select New Database, as shown in the following screenshot:
   
5. We can name it ns and leave the rest at their default values, and then click on OK. After that is done, go to the Database folder in Object Explorer.
6. Then, right-click on Tables, and click on Create New Table. Here, we need to enter a column name (for example, test), and choose nchar(10) as the data type. Then, click on Save Table and we are presented with a dialog box, which gives us the option to change the table name. Here, we can type test again.
7. We have now created a database called ns with a table called test, which contains a column also called test. This is an empty database that NetScaler will query to verify connectivity to the SQL server.

Now, we can go back to NetScaler and continue with the set up. First, we need to add a DBA user. This can be done by going to System | User Administration | Database Users, and clicking on Add. Here, we need to enter a username and password for a SQL user who is allowed to log in and query the database.

After that is done, we can create a monitor. Go to Traffic Management | Load Balancing | Monitors, and click on Add. As the type, choose MSSQL-ECV, and then go to the Special Parameters pane.

Here, we need to enter the following information:

• Database: This is ns in this example.
• Query: This is a SQL query, which is run against the database. In our example, we type select * from test.
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• User Name: Here we need to enter the name of the DBA user we created earlier. In my case, it is sa.
• Rule: Here, we enter an expression that defines how NetScaler will verify whether the SQL server is up or not. In our example, it is MSSQL.RES. ATLEAST_ROWS_COUNT(0), which means that when NetScaler runs the query against the database, it should return zero rows from that table.
• Protocol Version: Here, we need to choose the one that works with the SQL Server version we are running. In my case, I have SQL Server 2012.

So, the monitor now looks like the following screenshot:

It is important that the database we created earlier should be created on all the SQL servers we are going to load balance using NetScaler. So, now that we are done with the monitor, we can bind it to a service. When setting up the services against the SQL servers, remember to choose MSSQL as the protocol and 1433 as the port, and then bind the custom-made monitor to it. After that, we need to create a virtual load-balanced service. An important point to note here is that we choose MSSQL as the protocol and use the same port nr as we used before 1433.

We can use NetScaler to proxy connections between different versions of SQL Server. As our backend servers are not set up to connect the SQL 2012 version, we can present the vServer as a 2008 server. For example, if we have an application that runs on SQL Server 2008, we can make some custom changes to the vServer. To create the load-balanced vServer, go to Advanced | MSSQL | Server Options. Here, we can choose different versions, as shown in the following screenshot:

After we are done with the creation of the vServer, we can test it by opening a connection using the SQL Management Server to the VIP address. We can verify whether the connection is load balancing properly by running the following CLI command:

Stat lb vserver nameofvserver

Summary

In this article, we followed steps for setting up a load-balanced Microsoft SQL Server running on 2008 R2 remembering that using load balancing between the end clients and SQL Server requires that the databases on the SQL server are synchronized to ensure that the content that the user is requesting is available on all the backend servers.

Resources for Article:

• Understanding Citrix Provisioning Services 7.0
• Getting Started with the Citrix Access Gateway Product Family
• Managing Citrix Policies