Access hosting environment before building WebHost - asp.net-core

Question

In my Program.cs Main method, I would like to read user secrets, configure a logger and then build the WebHost.
public static Main(string[] args)
{
string instrumentationKey = null; // read from UserSecrets
Log.Logger = new LoggerConfiguration()
.MinimumLevel.Debug()
.WriteTo.ApplicationInsightsEvents(instrumentationKey)
.CreateLogger();
BuildWebHost(args).Run();
}
I can get to the configuration by building my own, but I quickly end up in a mess trying to access hosting environment properties:
public static Main(string[] args)
{
var envName = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") ?? "Production";
var configBuilder = new ConfigurationBuilder()
.SetBasePath(Directory.GetCurrentDirectory())
.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
.AddJsonFile($"appsettings.{envName}.json", optional: true, reloadOnChange: true);
// Add user secrets if env.IsDevelopment().
// Normally this convenience IsDevelopment method would be available
// from HostingEnvironmentExtensions I'm using a private method here.
if (IsDevelopment(envName))
{
string assemblyName = "<I would like the hosting environment here too>"; // e.g env.ApplicationName
var appAssembly = Assembly.Load(new AssemblyName(assemblyName));
if (appAssembly != null)
{
configBuilder.AddUserSecrets(appAssembly, optional: true); // finally, user secrets \o/
}
}
var config = configBuilder.Build();
string instrumentationKey = config["MySecretFromUserSecretsIfDevEnv"];
Log.Logger = new LoggerConfiguration()
.MinimumLevel.Debug()
.WriteTo.ApplicationInsightsEvents(instrumentationKey) // that.. escallated quickly
.CreateLogger();
// webHostBuilder.UseConfiguration(config) later on..
BuildWebHost(args, config).Run();
}
Is there an easier way to access IHostingEnvironment before building the WebHost?

Answer 1

In the main method, you cannot get the IHostingEnvironment instance before building the WebHost, as hosting is not yet created. And you cannot create a new valid instance properly, as it must be initialized using WebHostOptions`.
For application name you may use Assembly.GetEntryAssembly()?.GetName().Name
For environment name use what you currently do (I assume something like this is used in your IsDevelopment() method):
var environmentName = System.Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");
bool isDevelopment = string.Equals(
"Development",
environmentName,
StringComparison.OrdinalIgnoreCase);
See, methods like IHostingEnvironment.IsDevelopment() are extension methods that simply do string comparison internally:
public static bool IsDevelopment(this IHostingEnvironment hostingEnvironment)
{
if (hostingEnvironment == null)
{
throw new ArgumentNullException(nameof(hostingEnvironment));
}
return hostingEnvironment.IsEnvironment(EnvironmentName.Development);
}
public static bool IsEnvironment(
this IHostingEnvironment hostingEnvironment,
string environmentName)
{
if (hostingEnvironment == null)
{
throw new ArgumentNullException(nameof(hostingEnvironment));
}
return string.Equals(
hostingEnvironment.EnvironmentName,
environmentName,
StringComparison.OrdinalIgnoreCase);
}
Note regarding AddJsonFile: as file name is sensitive in Unix OS, sometimes it's better to use $"appsettings.{envName.ToLower()}.json" instead of.

Answer 2

I wanted to do something similar. I wanted to set Kestrel listen options based on the environment. I just save the IHostingEnvironment to a local variable while I am configuring the apps configuration. Then later on I use that variable to make a decision based on the environment. You should be able to follow this pattern to accomplish your goal.
public class Program
{
public static void Main(string[] args)
{
BuildWebHost(args).Run();
}
public static IWebHost BuildWebHost(string[] args)
{
IHostingEnvironment env = null;
return WebHost.CreateDefaultBuilder(args)
.UseStartup<Startup>()
.ConfigureAppConfiguration((hostingContext, config) =>
{
env = hostingContext.HostingEnvironment;
config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
.AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true);
if (env.IsDevelopment())
{
var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName));
if (appAssembly != null)
{
config.AddUserSecrets(appAssembly, optional: true);
}
}
config.AddEnvironmentVariables();
if (args != null)
{
config.AddCommandLine(args);
}
})
.UseKestrel(options =>
{
if (env.IsDevelopment())
{
options.Listen(IPAddress.Loopback, 44321, listenOptions =>
{
listenOptions.UseHttps("testcert.pfx", "ordinary");
});
}
else
{
options.Listen(IPAddress.Loopback, 5000);
}
})
.Build();
}
}

Answer 3

In .Net Core 2.0 you can do like this
var webHostBuilder = WebHost.CreateDefaultBuilder(args);
var environment = webHostBuilder.GetSetting("environment");