Azure Cloud Service - Configure Session from RoleEnvironment - asp.net-mvc

Question

Our application is hosted as a Cloud Service in Azure and we have all our connection strings and other connection-like settings defined in the ServiceConfiguration files. We are also using a Redis Cache as the session state store. We are trying to specify the Redis Cache host and access key in the ServiceConfig and then use those values for the deployment depending on where the bits land. The problem is session is defined in the web.config and we can't pull RoleEnvironment settings into the web.config.
We tried altering the web.config in the Application_Startup method but get errors that access is denied to the web.config on startup, which makes sense.
We don't really want to write deployment scripts to give the Network Service user access to the web.config.
Is there a way to setup session to use a different Redis Cache at runtime of the application?
The error that we are getting is "Access to the path 'E:\sitesroot\0\web.config' is denied'. I read an article that gave some examples on how to give the Network Service user access to the web.config as part of the role starting process and did that and then now we have access to the file but now get the following error "Unable to save config to file 'E:\sitesroot\0\web.config'."

Answer 1

We ended up being able to solve this using the ServerManager API in the WebRole.OnStart method. We did something like this:
using (var server = new ServerManager())
{
try
{
Site site = server.Sites[RoleEnvironment.CurrentRoleInstance.Id + "_Web"];
string physicalPath = site.Applications["/"].VirtualDirectories["/"].PhysicalPath;
string webConfigPath = Path.Combine(physicalPath, "web.config");
var doc = System.Xml.Linq.XDocument.Load(webConfigPath);
var redisCacheProviderSettings = doc.Descendants("sessionState").Single().Descendants("providers").Single().Descendants("add").Single();
redisCacheProviderSettings.SetAttributeValue("host", RoleEnvironment.GetConfigurationSettingValue("SessionRedisCacheHost"));
redisCacheProviderSettings.SetAttributeValue("accessKey", RoleEnvironment.GetConfigurationSettingValue("SessionRedisCacheAccessKey"));
redisCacheProviderSettings.SetAttributeValue("ssl", "true");
redisCacheProviderSettings.SetAttributeValue("throwOnError", "false");
doc.Save(webConfigPath);
}
catch (Exception ex)
{
// Log error
}
}