Invalid View State error While expanding your Web Farm

Last few days back, I faced one peculiar issue, while adding a new system in my Web Farm. My users started facing an issue “InValid View State” intermittently.

First, I could not guess what is the issue and thought of some programming issue. But later after analysis I found the issue is caused by the changes in the Web Farm.

Just before discuss the solution, Let’s analyse this.

First,  What is Web Farm?

A Web Farm is used in highly available applications and which have a lot of users that cannot be served by a single server. They provides better performance and are easily scalable. It means we’ll have multiple web servers behind a Network Load Balancer (NLB). Whenever a request comes, it first goes to the load balancer, which checks all the available web servers and finds the web server which has comparatively less requests to serve, and passes the request to that web server. Continue reading…

How to store custom objects in web.config

In this Post, I am going to discuss about web.config. Normally in our daily life, we used to have some data in appSettings section of web.config and read it when required. That is in string form. But there are lot more than this. We can update the data in web.config  programmatically as well .

Now another main point is, we can store some object of custom type in web.config as well, which we normally don’t do it. But this can be very useful in several scenarios.

Have anyone tried to update some value or add some value in web.config?  W’ll have brief discussion on this.

First, This is very common to have some constant data at appSettings section of web.config and read it whenever required. So how to read this ( for beginners).

//The data is stored in web.config as
<appSettings>
		<add key="WelcomeMessage" value="Hello All, Welcome to my Website." />
</appSettings>

// To read it
string message = ConfigurationManager.AppSettings["WelcomeMessage"];

Now if we want to update some data of appSettings programatically. One can do like this.

//Update header at config
        Configuration config = WebConfigurationManager.OpenWebConfiguration(Request.ApplicationPath);
        config.AppSettings.Settings["WelcomeMessage"].Value = "Hello All, Welcome to my updated site.";
        config.Save();

Now what do you do,  if you want to add some data in appSettings . You can add some app.config data as below.

//Update header at config
        Configuration config = WebConfigurationManager.OpenWebConfiguration(Request.ApplicationPath);
        config.AppSettings.Settings.Add("ErrorMessage", "An error has been occured during processing this request.");
        config.Save();

The above code is adding one new key value pair in web.config file.  Now this can be read anywhere in the application.

Now, the question is, Can we store some custom data at config?

Yes…

We can store some object. Let’s see how

I have created a sample example. In this example, I have saved an  object of my custom class NewError in web.config file. And also updating it whenever required.

To do this, Follow the below steps.

a) Create a Class that inherit From ConfigurationSection (It is available under namespace System.Configuration ).  Every property must have an attribute ConfigurationProperty, having attribute name and some more parameters. This name is directly mapped to web.config. Let’s see the NewError class

public class NewError:ConfigurationSection
{
    [ConfigurationProperty ("Id",IsRequired = true)]
    public string ErrorId {
        get { return (string)this["Id"]; }
        set { this["Id"] = value; }
    }
    [ConfigurationProperty("Message", IsRequired = false)]
    public string Message {
        get { return (string)this["Message"]; }
        set { this["Message"] = value; }
    }
    [ConfigurationProperty("RedirectURL", IsRequired = false)]
    public string RedirectionPage
    {
        get { return (string)this["RedirectURL"]; }
        set { this["RedirectURL"] = value; }
    }
    [ConfigurationProperty("MailId", IsRequired = false)]
    public string EmailId
    {
        get { return (string)this["MailId"]; }
        set { this["MailId"] = value; }
    }
    [ConfigurationProperty("DateAdded", IsRequired = false)]
    public DateTime DateAdded
    {
        get { return (DateTime)this["DateAdded"]; }
        set { this["DateAdded"] = value; }
    }
}

as you can see every property has attribute ConfigurationProperty with some value. As you can see the property ErrorId has attribute

 [ConfigurationProperty ("Id",IsRequired = true)]

it means ErrorId will be saved as Id in web.config file and it is required value. There are more elements in this attribute that you can set based on your requirement.
Now if you’ll see the property closely, it is bit different.

public string ErrorId {
get { return (string)this["Id"]; }
set { this["Id"] = value; }
}

Here the value is saved as the key “id”, that is mapped with web.config file.

b) Now you are required to add/register a section in the section group to tell the web.config that you are going  to have this kind of data. This must be in <configSections/>  and will be as

<section name="errorList"  type="NewError" allowLocation="true"
     allowDefinition="Everywhere"/>

c) Now one can add that object in your config file directly as

<errorList Id="1" Message="ErrorMessage" RedirectURL="www.google.com" MailId="xyz@hotmail.com" ></errorList>

d) And to read it at your page. Read it as follows.

NewError objNewError = (NewError)ConfigurationManager.GetSection("errorList");

And also a new object can be saved programmatically as

 NewError objNewError = new NewError()
        {
          RedirectionPage="www.rediff.com",
          Message = "New Message",
          ErrorId="0",
          DateAdded= DateTime.Now.Date
        };
        Configuration config =
            WebConfigurationManager.OpenWebConfiguration(Request.ApplicationPath);

        config.Sections.Add("errorList", objNewError);
        config.Save();

Even one can add a custom group and have some custom elements in in this section.

ASP.NET provides very powerfull APIs to read/edit the web.config file easily.

Hope you all must have enjoyed this, and I will appreciate your feedback.

Thanks