How do environment variables and appSettings file(s) get used during publish? - visual-studio

Question

If I have two settings files
appSettings.json and appSettings.Development.json
When I use publish from Visual Studio, are both supposed to be copied to the target folder? I'm not sure, because they both show up in the target folder (on a dev server) when I publish. I was under the impression that they combined at build time and ONLY the appSettings.json file was published. If not, then do I need to consider manually coding for these differences as Ive seen in a few examples ?
eg. This example is loading the settings via code (NOT how Im doing it)
Note - they are using the environment name, ASPNETCORE_ENVIRONMENT setting
public Startup(IHostingEnvironment env)
{
var builder = new ConfigurationBuilder()
.SetBasePath(env.ContentRootPath)
.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
.AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true)
.AddEnvironmentVariables();
Configuration = builder.Build();
}
Some of my Startup class is shown below.
Note: I am not referencing the environment setting.
public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
public IConfiguration Configuration { get; }
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
// In production, the Angular files will be served from this directory
services.AddSpaStaticFiles(configuration =>
{
configuration.RootPath = "ClientApp/dist";
});
}
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseExceptionHandler("/Error");
// The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
app.UseHsts();
}
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseSpaStaticFiles();
app.UseMvc(routes =>
{
routes.MapRoute(
name: "default",
template: "{controller}/{action=Index}/{id?}");
});
app.UseSpa(spa =>
{
// To learn more about options for serving an Angular SPA from ASP.NET Core,
// see https://go.microsoft.com/fwlink/?linkid=864501
spa.Options.SourcePath = "ClientApp";
if (env.IsDevelopment())
{
spa.UseAngularCliServer(npmScript: "start");
}
});
}
[ Update ]
I found my answer here - the key I was missing was updating the csproj file for the publish settings related to environment.
https://learn.microsoft.com/en-us/aspnet/core/host-and-deploy/aspnet-core-module?view=aspnetcore-2.2#configuration-with-webconfig
So I assume that if I have several different environments, each with its own settings file, that a publish would result in putting ALL of them out to the target dir?

Answer 1

It's a bit confusing with ASP.NET Core, especially if you're coming from having worked with ASP.NET previously. The build configurations (Debug, Release) really have no bearing on anything that happens with ASP.NET Core. An ASP.NET Core app is technically environment-agnostic. Whereas with an older ASP.NET app, you'd have to publish for a specific environment, you can theoretically take the same ASP.NET Core publish and run it in any of your environments. This is of course aided by the fact that Web.config is not utilized by ASP.NET Core.
This, then, is the reason why all the environment-specific JSON files come along for the ride. Which is ultimately used is based on the value of the ASPNETCORE_ENVIRONMENT environment variable set at runtime, not which build configuration you chose when publishing. Which is actually really nice when you think about it. You can take the same published app, run it in your "staging" environment to ensure everything is working and then deploy it to your "production" environment, simply by ensuring that each environment has the appropriate value for ASPNETCORE_ENVIRONMENT set. This makes release pipelines trivial.
That said, it's still possible to use things like the #if DEBUG compiler directives, and if you do that then there will be differences in your ASP.NET Core app depending on the build configuration chosen, but you should really avoid doing that in the first place. In general, you should rely only on the IHostingEnvironment abstraction in an ASP.NET Core app to determine what happens in what environment.