ASP.NET Core WebAPI 500 Internal error in IIS 7.5

Question

I'm struggling to get this WebAPI to work. Well, work with IIS. Everything works fine in IIS express, but when I publish it, specifically 1 api request doesn't work. I'm trying to access a url of API/[Controller]/{date}/{integer}. I keep getting the 500 server error. My other route of API/[Controller]/{date} works.

Here's my API Controller:

[Route("api/[controller]")]
    public class PostingsController : Controller
    {
        // GET: api/Postings/5
        [HttpGet("{date}")]
        public string Get(string date)
        {
            return date;
        }

        // GET api/Postings/20160407/2
        [HttpGet("{date}/{modeID}")]
        public List<TruckPosting> Get(string date, int modeID)
        {
            TruckPosting tp = new TruckPosting();
            List<TruckPosting> truckPostings = tp.GetTruckPostings(date, modeID);
            return truckPostings;
        }
    }

Could the reason be that I'm trying to return a List<>? I'm stumped considering it works fine in VS's IIS Express.

Edit

Here's my startup.cs page:

public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc();
        }

public void Configure1(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
            {
                app.UseIISPlatformHandler();
                app.UseDefaultFiles();
                app.UseStaticFiles();
                app.UseFileServer(true);
                app.UseMvc();
            }

            // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
            {
                app.Map("/appRoot", (app1) => this.Configure1(app1, env, loggerFactory));
            }

Answer 1

That's a good thought that it might that fact that you're returning a List. We have working Core Web API methods and all of them return Task<IEnumerable<Foo>>. Try changing the return type List<TruckPosting> to Task<IEnumerable<TruckPosting>>

EDIT: To view the details for 500 (internal server) errors you will need to put the following line of code at the beginning of your Configure (or Configure1) method:

app.UseDeveloperExceptionPage();   

And obviously this is not something you want in a production environment.

EDIT2: When running in VS you can use the code below to show exception details as long as the Hosting:Environment variable in the Debug section of Properties is set to "Development". After publishing you will need to create a System Environment variable named ASPNET_ENV and set its value to "Development" or the code will not call the UseDeveloperExceptionPage() method.

if (env.IsDevelopment())
{
    app.UseDeveloperExceptionPage();
}