Introduction to Multi-Tenant Architecture

The following code listing shows a page sending an email after a user registers for the site. Typically upon registration, some sort of email is sent to give that sense of confirmation or welcome message to the new user. If I had multiple tenants, I couldn't store the email settings in the Web.config because each site may want a different subject, body, and so forth. And, you definitely do not want to hard code for each case!!

namespace MultiTenantSite
{
   public partial class _Default : System.Web.UI.Page
   {
      protected void Page_Load(object sender, EventArgs e)
      {

      }

      protected void CreateUserWizardControl_CreatedUser(object
         sender, EventArgs e)
      {
         // Create the Mail Message from the Cached App Settings
         // For the Tenant
         MailMessage confirmEmail = new MailMessage()
         {
            From = new MailAddress(new Data.AppSettings()
               ["Site.Registration.Email.From"]),
            Subject = new Data.AppSettings()
               ["Site.Reigstration.Email.Subject"],
            Body = new Data.AppSettings()
               ["Site.Registration.Email.Body"],
         };

         // Create the SMTP Client and Send the Message
         SmtpClient emailSender = new SmtpClient("Some SMTP Host");

         emailSender.Send(confirmEmail);

      }
   }
}

Using a Content Management System

The next component to a multi-tenant application, a Content Management System (CMS), is optional but will help to display content dynamically on-demand for tenants that use the site. Designing a CMS can be an article within itself. Really, in this situation, you would want to use the CMS system to create content in a web-part format. You then can use these web parts interchangeably and on demand as you design your pages for a tenant. Typically, if the content is static with only different app settings and different App Themes, a CMS may not be needed.

To illustrate what I am talking about, assume I have a CMS system for a Multi-Tenant site where a database drives the system and stores web parts that are created are stored through some web part manager on the site. Now, in the actual solution, I have a footer control that is rendered on the master page, and on the footer I have three links: FAQ, Contact Us, and About. Each tenant that is using this base website may have different text that will need to be displayed for each link. With a Multi-Tenant site powered by CMS, I could create web parts for each different link for each tenant and set the PostBackUrl Property of each link button through the app settings.

Footer Markup

<table width="100%">
   <tr>
      <td align="center">
         <asp:LinkButton runat="server" ID="lnFAQ">
         </asp:LinkButton>
      </td>
      <td align="center">
         <asp:LinkButton runat="server" ID="lnContactUs">
         </asp:LinkButton>
      </td>
      <td align="center"><asp:LinkButton runat="server"
                                         ID="lnAbout">
         </asp:LinkButton>
      </td>
   </tr>
</table>

Code Behind (Setup Links)

public partial class Footer : System.Web.UI.UserControl
   {
      protected void Page_Load(object sender, EventArgs e)
      {
         // Set the Post Back URLs for each link
         lnContactUs.PostBackUrl =
            GetRelativeCmsUrl("Site.Link.ContactUs");
         lnFAQ.PostBackUrl = GetRelativeCmsUrl("Site.Link.FAQ");
      }

      public static string GetRelativeCmsUrl(string configKeyName)
      {
         // return link to the CMS Page that Handles Web Parts,
         // Retrieve the ID of the Web Part from the
         // Cached App Settings
         return (String.Format("~/cms/page.aspx?ContentID={0}",
                 new Data.AppSettings()[configKeyName]));
      }
   }

IIS Setup

The last piece to successfully implement a Multi-Tenant Web Site is setting up IIS to handle each website. This is a relatively simple concept, especially if you have already set up a basic ASP.NET website in IIS. To make this a little more complex and really demonstrate where Multi-Tenant architecture is handy, assume your server has only one public facing IP to register a website under. First, you will need to create a new website for each tenant. One problem with this: You need to assign an IP to each site but you only have one. A solution to this is to use host headers for each site, map each host header to the single IP, and then register the host headers with your respective DNS server.