Transforming Web.config appSettings for Microsoft Azure Cloud service

WebRole.cs

using System.Linq;
using Microsoft.Web.Administration;
using Microsoft.WindowsAzure.ServiceRuntime;

namespace Microsoft.Portal.Extensions.NewRelic_AzurePortal_APM
{

    // Credit goes to Andy Cross, azurecoder, and Beth Martin from the Elastacloud blog and Steven Kuhn:
    // http://blog.elastacloud.com/2011/05/13/azure-howto-programmatically-modify-web-config-on-webrole-startup/
    
    /*
    In your ServiceConfiguration.csdef you'll need to have two things:
    1. A setting defined inside the WebRole element
      <ConfigurationSettings>
		    <Setting name="NewRelic.AppName" />
      </ConfigurationSettings>
    
    2. <Runtime executionContext="elevated" /> for executing the transform
    
    In any *.cscfg you need to specify a setting with the same name you did in the WebRole.cs
    <ConfigurationSettings>
      <Setting name="MySetting" value="MyValue" />
    </ConfigurationSettings>
    */
    
    public class WebRole : RoleEntryPoint
    {
        public override bool OnStart()
        {
            ConfigureNewRelic();

            return base.OnStart();
        }

        private static void ConfigureNewRelic()
        {
            if (RoleEnvironment.IsAvailable && !RoleEnvironment.IsEmulated)
            {
                string settingValue;
                try
                {
                    settingValue = RoleEnvironment.GetConfigurationSettingValue("[SETTING_NAME]");
                }
                catch (RoleEnvironmentException)
                {
                    /*nothing we can do so just return*/
                    return;
                }

                if (string.IsNullOrWhiteSpace(settingValue))
                    return;

                using (var server = new ServerManager())
                {
                    // get the site's web configuration
                    const string siteNameFromServiceModel = "Web";
                    var siteName = string.Format("{0}_{1}", RoleEnvironment.CurrentRoleInstance.Id, siteNameFromServiceModel);
                    var siteConfig = server.Sites[siteName].GetWebConfiguration();

                    // get the appSettings section
                    var appSettings = siteConfig.GetSection("appSettings").GetCollection();
                    AddConfigElement(appSettings, "[APP_SETTING_NAME]", settingValue);
                    server.CommitChanges();
                }
            }
        }

        private static void AddConfigElement(ConfigurationElementCollection appSettings, string key, string value)
        {
            if (appSettings.Any(t => t.GetAttributeValue("key").ToString() == key))
            {
                appSettings.Remove(appSettings.First(t => t.GetAttributeValue("key").ToString() == key));
            }

            var addElement = appSettings.CreateElement("add");
            addElement["key"] = key;
            addElement["value"] = value;
            appSettings.Add(addElement);
        }

    }
}

@bkrauska

Sorry to be so obscure there. A web role will always have a suffix of "_web" so the actual value coming out from the formatter will look something like: MyWebRoleName_IN_0_web - it's a convention used by Microsoft to segment settings.