Handle multiple web.configs based on URL - asp.net

Question

We currently have an application which is used against multiple regional databases. The codebase is exactly the same but it is rolled out on the webserver in 3 different directories each with its own web.config (to hit the correct database and get correct app settings). Each with its own IIS environment.
However, my manager wants this changed i.e. One IIS application which will dynamically load up the correct web.config file for each region.
I will attempt to load the correct web.config file based on a query parameter when logging in but I have no idea on how to load the web.config file when logging in.
Anyone with experience doing this .... is there a better solution?

Answer 1

Based on your comment here's a different approach. You have a little work to do.
Routing all the domains to the same web site
I'm assuming you have one domain name per region (e.g. Region1.WebSite.com, Region2.WebSite.com, etc.) Combining these into one physical web site is a little tricky because of SSL certificate required. Has to match.
Two options:
Drive all three domains to the same web server via three different internal IP addresses. This means three sets of bindings in IIS and three different certs.
Use SSL offloading and terminate SSL at the load balancer. Direct all three sites to the same internal IP address on IIS. Make sure you have configured the LB to forward the original host header.
Detect where the request came from
In ASP.NET code, you can use the host header to see what domain the request was submitted over, e.g.
var siteRequested = Request.Headers["Host"];
Use the host header to pick a connection string
You will need several entries in web.config, one for each connection string. Format the name of the connection string to include the host name, so that you can obtain the right string by using something like this:
var configItemName = "ConnectionString." + Request.Headers["Host"];
var connectionString = System.Configuration.ConfigurationManager.ConnectionStrings[configItemName].ConnectionString;
Your web.config connection strings should look something like this:
<connectionStrings>
<add name="ConnectionString.Region1.WebSite.com" connectionString="Data Source=serverNameForRegion1;Et Cetera" />
<add name="ConnectionString.Region2.WebSite.com" connectionString="Data Source=serverNameForRegion2;Et Cetera" />
<add name="ConnectionString.Region3.WebSite.com" connectionString="Data Source=serverNameForRegion3;Et Cetera" />
</connectionStrings>
Store any remaining region-specific configuration in the database
Each database will have its own copy of configs, so you just need to retrieve them using the correct connection string and you'll get the right configs.

Answer 2

You can keep a common web.config, but then move a portion of it to a separate file, using ConfigSource. See this question for details.
Once you have some configs in a separate file, you can choose a different file at runtime:
In ASP.NET applications, at run time you can assign to the ConfigSource property the name of an alternative configuration file.
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