Session management using SQL Azure and Update on automatic session clearance

Session management using InProc in azure roles is dangerous thing!!!

Why InProc is dangerous?

Create an azure cloud service project and add a web role in it. Then I added a sample page named as Session demo in it. To test the session data saving and retrieval I added following control in the <form> control present on the page –

<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>

<asp:Button ID="btnAddToSession" runat="server" OnClick="btnAddToSession_Click" Text="Add To Session!!" />

            <br />

            <br />

            <asp:Button ID="btnReadFromSession" runat="server" OnClick="btnReadFromSession_Click" Text="Read From Session!!" />

            <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>

            <br />

            <br />

            <asp:Label ID="lblInstanceId" runat="server" Text="Label"></asp:Label>

On the code behind I added below simple code to add values in session and retrieve it. Also in page load event I am retrieving the id of role instance to check that, my current request is being served from which instance.

public partial class SessionDemo : System.Web.UI.Page

    {

        protected void Page_Load(object sender, EventArgs e)

        {

            lblInstanceId.Text = "You are being served from - "+ RoleEnvironment.CurrentRoleInstance.Id;       

 } 

        protected void btnAddToSession_Click(object sender, EventArgs e)

        {

            Session["MySession"] = TextBox1.Text;

        } 

        protected void btnReadFromSession_Click(object sender, EventArgs e)

        {

            if (Session["MySession"] != null)

                Label1.Text = Session["MySession"].ToString();

        }

    }

In web.config file as shown below, I have configured my session state as InProc under <system.web> tag –

<sessionState mode="InProc"/>

Now right click on cloud Service project, select Properties and set the application to run in full emulator and full IIS as shown below -

 

Note – The option to run the cloud service project locally in Full Emulator mode is applicable till the Azure SDK 2.3 only. In Azure SDK 2.4, full emulator is deprecated. I don’t know the reason why they have deprecated full emulator mode in Azure SDK 2.4.

Now we always should set the number of instances for an azure role as minimum of 2. Therefore right click on web role node present in cloud service project and in properties set the instance count as 2.

 

 

 

We all set to see how InProc session management in Azure web role is devil. Set the cloud service project as startup project and I have set the Sessiondemo.aspx page as startup page and here I click F5. And here what I see on my page and in my IIS –

So as you can see, in IIS there are two instances got created as expected and below that the UI shows simple design to test sessions. Also if you see in IE, my current request is being server from INSTACE 0.

Now let’s say I add the value to session as “kunal” by clicking on button “Add to Session” and retrieve it from session by clicking on button “Read from Session” and I found that, my requests are still getting served from INSTACE 0 and session value is being retrieved correctly. Now I right click on instance 0 website in IIS and then I select the options as Manage Web Site | Stop. This actually stops the 0^th instance running in IIs. Remember, my project is still running in debug mode. I just stopped one of the role instances of my azure application.

Once the IIS website is stopped you can view the black icon on the web site as shown. This confirms that my website is stopped.

Now I refresh my browser 2-3 times. This means now my request will start getting served from INSTANCE 1 of IIS website because instance 0 is stopped and here is what I see –

As you can see above, my request is being served from INSTACE 1 and my Session value is not retrieved on refresh. Therefore I click on button “Read from session” again and DAMN!!!

I am not receiving the value “kunal” that I had added in my session. This is the problem!!! Ideally I should have received my session values irrespective from which instance of role my request is getting served.

In Azure environment there is always possibility that, the instance of role gets recycled due to hardware failures or other errors. Means if you configure only 1 instance for your role then there is possibility that, your role instance is down and you DON”T GET HIGH AVAILABILITY for your application. Therefore it is always BEST PRACTICE TO HAVE ATLEAST 2 INSTANCE for your azure role.

But again, if you have 2 instance configured for your web role then session management using INPROC will not work as shown above!!!

What is the Solution?

You should always store the session state outside your role environment. How do I do that?

Transient Fault Handling with SQL Azure and Entity Framework step by step guide

Communication errors are always a pain!! When you are working with cloud platform like Azure, communication errors makes you feel the pain even more!!

Thanks that Transient Fault Handling framework exists!!

Alright guys, so here I am going demonstrate how to configure transient fault handling application block of Enterprise Library 6 (and above hopefully, if they don’t change in next versionsJ) with SQL Azure and Entity framework. This going to be a long article that is what I think. So be ready!!

What are Transient Faults or Transient Errors?

These are mainly network issues. If you perform an operation in Azure and sometimes it does not work however if you try after some time, it works well. This odd and non-predictable behavior is nothing but transient faults.

When we talk about SQL Azure, transient faults are common. The article Azure SQL Database Resource Management - http://msdn.microsoft.com/library/azure/dn338083.aspx mentions the scenarios in which you may face transient fault of SQL Azure.  I highly recommend you to go through the all this documents and related links. Very informative!!

Now, very common transient error of SQL Azure is throttling.

What is throttling?

Throttle is very common term used in computing and networking. The dictionary meaning of throttle is to kill or stop something. Throttling can be of any type like, network throttling, bandwidth throttling, and email throttling and so on.  Throttling can be sometime good and sometime bad. When it is bad for you, it is your responsibility to handle it. Throttling is good when the database server engine is experiencing extreme load and it is well above the desired load. Then throttling brings down consumption of resource and frees some of the load of database engine. This is done via blocking the connections or denying the new connections to SQL Azure database engine. It is bad when you are trying to connect to SQL Azure and throttling occurs and you get connectivity errors with SQL Azure. To understand more about SQL Azure throttling refer to the link - http://msdn.microsoft.com/en-US/library/azure/dn338079.aspx.

Solution -

The solution is simple and you are advised to implement retry logic in your application. To implement retry logic in SQL Azure and entity framework, we use Transient Fault Handling block. It is simple and recommended to always use Transient Fault Handling framework to deal with SQL Azure connectivity errors and have retry logic in application.

Implementation –

Please note that, I am using Transient Fault Handling Block version 6.0.1304. This is the one available as of today (7^th July 2014). Also I am using Azure SDK 2.3 and visual stiudio 2013 for this sample.

First let’s create a server in SQL Azure and add a database in it. I created simple database named as Company and added only one table in it named as Customer with 3 columns and sample data as shown in below screenshot.