Azure App Service: Sessions Management in Load Balancing Environment Using Redis Cache

Clicking on the Login button will NOT guarantee that the form will be posted to 10.202.174.84. It might post the data to the other server which in my case is “10.202.116.91”.

In my case, when I clicked on the “Login” button of the above screen capture, it took me to the Default page with the following values.

• IP Address is 10.202.174.84 (this is the same in my login Page).
• Session is NULL. The reason is, when login is clicked, the request might have gone to the other instance (“10.202.116.91”) where my session got stored.
• Refresh the page a couple of times.
  

Please observe the following.

• Session has some value “admin”.
• IPAddress is 10.202.116.91.

So, the conclusion here is “Sessions” wouldn’t work as expected in the Azure App Service when you configure Load Balancer using the auto-scaling feature.

Here comes the savior. The Redis Cache provider. Below is the definition from the Azure Official Web site.

Azure Redis Cache is based on the popular open-source Redis cache. It gives you access to a secure, dedicated Redis cache, managed by Microsoft and accessible from any application within Azure.

Below are the steps required to make our sessions work as expected.

• Create the Redis Cache from the Azure Management Portal.
• Configure the Application to use the Azure Redis Cache.
• Use the Sessions.

Create the Redis Cache from the Azure Management Portal.

Let’s start creating the Redis Cache using the Azure Management Portal as shown below.

Provide the details of the Redis Cache as shown below.

Click on the “Create” button of the above screen capture. It will take a couple of minutes to create the Redis Cache.

Configure the Application to use the Azure Redis Cache

Let’s configure the application to use the Redis Cache that we have just created.

As shown in the above screen capture, go-to Package Manager Console and type the command “Install-Package StackExchange.Redis” and click “Enter”.

Now, we have successfully installed the required packages. (Please note that your .NET framework should be 4 or higher.)

In order to use the assemblies, we need to first added the following namespace to both our Login.aspx page and Default.aspx page.

Using StackExchange.Redis;

Let’s add a new class named “RedisConnection” to the project. Please refer the attached Project.

In order to connect to Redis Cache, we need to pass the following information to the ConnectionMultiplexer.Connect function. Let’s grab them from the Portal.

• Redis Cache URL.
• Keys.

Please don’t save the Keys in Code. To make things simple, I am storing the keys in the Source Code. Please refer this page which provides information on how to store the credentials.

We are now ready with the class that could be used to connect to the Redis Cache. Let’s use the class to create session in the Redis Cache.

Open your Login.aspx.cs file and replace the following line of code.

Session["login"] = this.txtUsername.Text.Trim();

With.

IDatabase cache = RedisConnection.Connection.GetDatabase();
cache.StringSet("login", this.txtUsername.Text.Trim());

Open the Default.aspx.cs and replace the following line of code.

protected void Page_Load(object sender, EventArgs e)
{
    if (Session["login"] == null)
    {
        Response.Write("Session is NULL. You are in " + Request.ServerVariables["LOCAL_ADDR"]);
    }
    else
    {
        Response.Write("Logged in user is " + Session["login"] + ". You are in " + Request.ServerVariables["LOCAL_ADDR"]);
    }
}

With.

protected void Page_Load(object sender, EventArgs e)
{
    IDatabase cache = RedisConnection.Connection.GetDatabase();
    string strLoginValue = cache.StringGet("login");

    if (strLoginValue == null)
    {
        Response.Write("Session is NULL. You are in " + Request.ServerVariables["LOCAL_ADDR"]);
    }
    else
    {
        Response.Write("Logged in user is " + strLoginValue + ". You are in " + Request.ServerVariables["LOCAL_ADDR"]);
    }
}

Let’s deploy the code to the Azure App Service and review the changes and navigate to the Login Page as shown below.

Notice the IPAddress. It’s 10.202.174.84. Now click on “Login” button. You will be taken to the Default.aspx page as shown below.

Notice that in the above screen capture, though the IPAddress is different, still we are able to see the username “admin” because the sessions are now stored in a distributed location “Redis Cache” which is accessible for both the instances.

Now, keep refreshing the page multiple times. You will notice that the IP Addresses are changing but not the value of the username.

That’s it. We have learned how to store the sessions in a load Balancing Environment. You can store any kind of data in Redis Cache.

Hope you enjoyed reading the article. Your feedback is really appreciated.