For IISExpress it will use the settings in launchSettings.json in the Properties folder of the web app.
If you launch the web command using VS (ie debugging) I think it will also use settings from that file.
But if you use the web command from the command line without VS I think it will use the default runtime from your user profile as shown by the dnvm list command.
Example launchSettings.json from my project:
{
"iisSettings": {
"windowsAuthentication": false,
"anonymousAuthentication": true,
"iisExpress": {
"applicationUrl": "http://localhost:54671/",
"sslPort": 0
}
},
"profiles": {
"IIS Express": {
"commandName": "IISExpress",
"launchBrowser": true,
"environmentVariables": {
"ASPNET_ENV": "Development"
},
"sdkVersion": "dnx-coreclr-win-x86.1.0.0-rc1-update1"
},
"web": {
"commandName": "web",
"environmentVariables": {
"Hosting:Environment": "Development"
},
"sdkVersion": "dnx-coreclr-win-x86.1.0.0-rc1-update1"
}
}
}