Reference same Connection String in Multiple .NET Applications

Question

I'm not sure if this is the correct medium for this question, so if it's not please inform me and I will correct.

As an example to illustrate my point, let's say I have 30 .NET applications that are published to 2-3 different web servers. Now, these applications are Intranet based, so I have a C# library that I reference in each of those applications. This library is comprised of methods that I use in each application to find out employee information if necessary. Now, the library has one connection string, but then I have to also reference that same connection string in all of the 30 applications... so if the database changes that the library is referencing, then I have to remember all 30 applications and change each of them individually.

Is there a way to put the connection string in some sort of file (text file, or something), and have each web.config in each of the 30 applications reference that specific file, so if the connection string needs to be changed, I can just change it in the file and then all 30 applications are still okay, or is there not something like that?

UPDATE

Okay, I now know how to reference a text file for connection string purposes.. but, it seems as though I only can do one of two options... either reference my primary connection string and library connection string individually within the web.config like so:

OPTION ONE

<connectionStrings>
  <add name="PrimaryCS" // more data />
  <add name="LibraryCS" // more data />
</connectionStrings>

This option would require me to change the LibraryCS connection string in each of the 30 applications if it were ever to be changed (NOT WHAT I WANT)

OPTION TWO

<connectionStrings configSource="MyConfig.config"></connectionStrings>

This option forces me to put both connection strings in the MyConfig.config file and not just the LibraryCS file.. so this would result in me having to change the LibraryCS connection string in every MyConfig.config file for each of the 30 applications (AGAIN, NOT WHAT I WANT).

WHAT I'M LOOKING FOR

I am looking for a mixture of the two options, but it seems this can't be done, so I'm hoping someone on this medium knows a work-around

<connectionStrings configSource="MyConfig.config">
  <add name="PrimaryCS" // more data />
</connectionStrings>

I want the MyConfig.config file to only hold the LibraryCS connection string and then have the main PrimaryCS connection string be separate.. so that if the LibraryCS connection string were ever needed to be changed, then I only have to do it in one place.

Answer 1

Microsoft has an amazing documentation about it. Hopefully that helps.

To store connection strings in an external configuration file, create a separate file that contains only the connectionStrings section. Do not include any additional elements, sections, or attributes. This example shows the syntax for an external configuration file.

<connectionStrings>  
  <add name="Name"   
   providerName="System.Data.ProviderName"   
   connectionString="Valid Connection String;" />  
</connectionStrings>

In the main application configuration file, you use the configSource attribute to specify the fully qualified name and location of the external file. This example refers to an external configuration file named connections.config.

<?xml version='1.0' encoding='utf-8'?>  
<configuration>  
    <connectionStrings configSource="connections.config"/>  
</configuration>

Source : https://learn.microsoft.com/en-us/dotnet/framework/data/adonet/connection-strings-and-configuration-files

Answer 2

One solution I came up with is to create a shared connection string file and reference it in the web.config of multiple web application projects.

So in my web configs I have this:

<connectionStrings configSource="configs\connectionStrings.local.config">

This file just contains the 'connectionStrings' portion of the config.

And I copy in the connectionStrings.local.config file into the configs folder on build of the project from a common solution folder (the config file is added to the solution as a solution item.

Other alternatives would be to use an environment variable on the servers to store the connection string or as people are mentioning a common file (just read the file as you would any text file).

Answer 3

Have you considered using Apache Zookeeper? Your use case seems to fit its' definition:

ZooKeeper is a centralized service for maintaining configuration information...

You can start a ZooKeeper instance somewhere and keep in it your configuration settings. Your settings will be organized in a structure similar to a file system structure. It may look like this (using zkCli.sh that comes with ZooKeeper to create the configuration, as an example):

create /common-settings
create /common-settings/connectionString 1.1.1.1:123
...
create /app-1-settings
create /app-1-settings/app-specific-setting myArbitrarySetting 

You can then set up your apps to include a ZooKeeper client, so that they are able to read the configuration you stored. For .NET, I have found https://github.com/shayhatsor/zookeeper, which seems to meticulously mimic the Java client: https://github.com/ewhauser/zookeeper.
I haven't used it extensively, but I got the following working (note C# 7.1+, due to async Main()):

using System;
using System.Text;
using System.Threading.Tasks;
using org.apache.zookeeper; // NuGet: ZooKeeperNetEx

namespace Example 
{
    // Watcher will notify us of events we get from ZooKeeper
    class MyWatcher : Watcher 
    {
        public override async Task process(WatchedEvent @event)
        {
            Console.WriteLine($"Process event: {@event}");
        }
    }   

    class Program 
    {
        async static Task Main()
        {
            // Create a new ZK client.
            var zookeeper = new ZooKeeper("<zookeeper-url>", sessionTimeout: 3000, new MyWatcher());
            // Use it to request a config setting.
            var connectionData = await zookeeper.getDataAsync("/common-settings/connectionString");
            // Convert the received data from bytes to string.
            var connectionString = Encoding.UTF8.GetString(connectionData.Data);

            Console.WriteLine($"Got connectionString '{connectionString}'."); // Got connectionString '1.1.1.1:123'
            Console.Read();
        }
    }
}

I'm sure that with little effort you can adapt it to your specific needs.
To get started with ZooKeeper, you could look into their Getting Started.
There's lots of info on the Internet too, of course.

Answer 4

A nifty solution is adding config file shortcuts in other projects so you only update one file:

It's similar to Sharing Assembly Files (demo'd in answer #2: https://stackoverflow.com/a/15319582/495455)

If you need more environments use Transforms:

I know this is a short answer, I like the really simple solutions. Let me know if you have any questions.

Answer 5

Don't know if this is what you are searching for, but when you overload the constructor of your ApplicationDbContext you can specify which connectionstring it should use:

public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{
    public ApplicationDbContext() : base(GetConnectionStringName(), throwIfV1Schema: false)
    {
    }

    static string GetConnectionStringName()
    {
         // Your logic for the connectionstring, I use the Request.Url here.
         return HttpContext.Current.Request.Url.Authority.ToLower().Split(new char[] { ':' }).FirstOrDefault().Replace("www.", "");
    }
}