asp.net core 2 web api set hosting url from appsettings

Question

On an asp.net core 2 web api, I want to be able to set the url on which my api will listen (api run as windows service) based on a value in appsettings.json file. I can't find a way to achive it, how can I have acces to an instance of IConfiguration ?

var pathToExe = Process.GetCurrentProcess().MainModule.FileName;
var pathToContentRoot = Path.GetDirectoryName(pathToExe);

return WebHost.CreateDefaultBuilder(args)
    .UseContentRoot(pathToContentRoot)
    .UseStartup<Startup>()
    .UseUrls({value_from_appsettings})
    .Build()
    .RunAsService();

This might be helpful. Ultimately, you have to create your own instance of IConfiguration. — Kirk Larkin
– Kirk Larkin, Commented Feb 16, 2018 at 16:47

Kirk Larkin · Accepted Answer · 2018-02-16 20:01:08Z

2

In order to gain access to the configuration before you go down the WebHost.CreateDefaultBuilder path, you'll need to build your own IConfiguration instance using ConfigurationBuilder.

Taking the example from your question, you can use something like the following:

var pathToExe = Process.GetCurrentProcess().MainModule.FileName;
var pathToContentRoot = Path.GetDirectoryName(pathToExe);

var appSettingsConfiguration = new ConfigurationBuilder()
    .SetBasePath(pathToContentRoot)
    .AddJsonFile("appsettings.json")
    .Build();

return WebHost.CreateDefaultBuilder(args)
    .UseContentRoot(pathToContentRoot)
    .UseStartup<Startup>()
    .UseUrls(appSettingsConfiguration["Your:Value"])
    .Build()
    .RunAsService();

This is somewhat explained in the docs where the example uses instead a hosting.json file to set this up. It also makes use of UseConfiguration, which allows you to specify a value for e.g. urls, which will be picked up automatically.

edited Feb 16, 2018 at 20:01

answered Feb 16, 2018 at 18:49

Kirk Larkin

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3 Comments

Nicolas Boisvert Over a year ago

I have a hard time to have access to environment name to add appSettings.{environment}.json file, how can I have access to it ?

Kirk Larkin Over a year ago

Try this for inspiration. i.e. Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT")

Kirk Larkin Over a year ago

An alternative would be to do it the same way WebHostBuilder does it, but that involves creating yet another IConfiguration first.

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