"No such host is known" when publishing locally, but not when debugging in Visual Studio

Question

Related: No such host is known —> System.Net.Http.HttpRequestException:

So, I have an odd problem: whenever I perform any call to a RESTful API using HttpClient, I get a the following error: System.Net.Http.HttpRequestException: No such host is known

I've seen several other Q&As that discuss this, but many of these (such as the one I link to) discuss it specifically in the context of an Azure VM. Many of them suggest that this is caused by a DNS issue.

My situation is a little different the other Q&As I've read, though: when I run my web site by debugging in Visual Studio 2019, it runs just fine. However, when I publish to IIS locally, I get this exception whenever I try to do a call to HttpClient.

Also, unlike some of the other articles I've read about this, this does not happen intermittently for me - it happens every single time I try to do an API call.

If this is caused by a DNS issue like some of the other Q&As suggest, that suggests that there must be some difference between when I publish locally and when I debug in Visual Studio.

Here's how I configure my Publish (summary of the image below for those who prefer text):

Image summary:

Web Deploy with WebPublishMethod MSDeploy
TargetFramework netcoreapp3.1
LastUsedBuildConfiguration Release
LastUsedPlatform x86
SelfContained false
MSDeployPublishMethod InProc
MSDeployServiceURL localhost

Additional details: - Destination URL http://localhost:80 - IIS Application Pool is set to "No managed code", as is usually suggested

Also, this occurs regardless of how I create the HttpClient instance and the code works just fine when debugging, so I think that this is more likely to be a configuration issue than a code issue, but for what it's worth, I use the following code in my Startup class to create it. (See also here for reference).

       services.AddHttpClient("MyNamedClient", (sp, c) =>
        {
            c.BaseAddress = new Uri("https://api.smartrecruiters.com/");

            c.Timeout = new TimeSpan(4, 0, 0);

            c.DefaultRequestHeaders.Accept.Clear();

            c.DefaultRequestHeaders.Add("Accept", "application/json");

            var ctx = sp.GetService<DatabaseContext>();

            Security security = ctx.Security.First();

            c.DefaultRequestHeaders.Add("APIToken", security.Apikey);
        });

I then use ASP.NET Core's Dependency Injection to get a HttpClient instance whenever I need it.

I also tried creating HttpClient as a singleton (which I know is not the recommended way of doing this in an ASP.NET Core application), but I had the same problem with that approach.

Here's the full error details from Event Viewer from when I try to do a GetAsync call using HttpClient:

Category: Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware
EventId: 1
RequestId: 8000000c-0006-ff00-b63f-84710c7967bb
RequestPath: /UsersObject/GetUsersAPICall
SpanId: |f32bc4b9-41d453941179fa9f.
TraceId: f32bc4b9-41d453941179fa9f
ParentId: 

An unhandled exception has occurred while executing the request.

Exception: 
System.Net.Http.HttpRequestException: No such host is known.
 ---> System.Net.Sockets.SocketException (11001): No such host is known.
   at System.Net.Http.ConnectHelper.ConnectAsync(String host, Int32 port, CancellationToken cancellationToken)
   --- End of inner exception stack trace ---
   at System.Net.Http.ConnectHelper.ConnectAsync(String host, Int32 port, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.ConnectAsync(HttpRequestMessage request, Boolean allowHttp2, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.CreateHttp11ConnectionAsync(HttpRequestMessage request, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.GetHttpConnectionAsync(HttpRequestMessage request, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.SendWithRetryAsync(HttpRequestMessage request, Boolean doRequestAuth, CancellationToken cancellationToken)
   at System.Net.Http.RedirectHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
   at System.Net.Http.DiagnosticsHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
   at Microsoft.Extensions.Http.Logging.LoggingHttpMessageHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
   at Microsoft.Extensions.Http.Logging.LoggingScopeHttpMessageHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
   at System.Net.Http.HttpClient.FinishSendAsyncBuffered(Task`1 sendTask, HttpRequestMessage request, CancellationTokenSource cts, Boolean disposeCts)
   at [Namespace].MyHttpClient.GetAsyncWithRetries(HttpClient client, String url) in C:\Users\[Removed]\source\repos\[Removed]\MyhHttpClient.cs:line 54
   at SR_Interaction.Models.SRUser.Search(String emailAddress, HttpClient client) in C:\Users\[Removed]\Models\SRUser.cs:line 100
   at Bosch_Live_Docs.Controllers.UsersObjectController.GetUsersAPICall(String query) in C:\Users\[Removed]\Controllers\UsersObjectController.cs:line 58
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterAsync>g__Awaited|13_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.<Invoke>g__Awaited|6_0(ExceptionHandlerMiddleware middleware, HttpContext context, Task task)

Anyone have any suggestions about how I might be able to fix this? I think it's probably either my IIS configuration or my publish settings - or am I on the wrong track entirely here?

Edit: As requested, here's the controller code:

    [HttpGet]
    [Authorize(Roles = "CreateUser,PatchUser")]
    public async Task<IActionResult> GetUsersAPICall([Bind("query")] [RegularExpression(@"^\w+(\.\w+)*@\w+(\.\w+)+|(\w+(\s\w+)*)$", ErrorMessage = "This does not look like a valid query")] string query)
    {
        if (query == null)
        {
            return BadRequest();
        }
        else if (!ModelState.IsValid)
        {
            // TODO: What to do with this? How do we actually show the validation error?
            return BadRequest("Does not look like a valid query");
        }

        List<SRUser> users = await SRUser.Search(query, clientFactory.CreateClient(Startup.srNamedClient));

        users = users.OrderBy(ur => ur.firstName).ToList();

        if (users.Any())
        {
            return PartialView("_UserList", users);
        }
        else
        {
            return NotFound();
        }
    }

And here's where I do the actual call:

public static async Task<List<SRUser>> Search(string emailAddress, HttpClient client)
    {
        string json;

        using (HttpResponseMessage msg = await client.GetAsync("user-api/v201804/users?limit=100&q=" + emailAddress))
        {
            json = await msg.Content.ReadAsStringAsync();
        }

        return JsonSerializer.Deserialize<NextPageContainer<SRUser>>(json).content;
    }

Further edit:

Here's the Application Pool:

Here are the modules I have installed:

I'm slightly confused about this particular one:

Is it necessary to include both? When I look at the Ordered view, the "old" one is actually higher:

However, I can't reorder it.

Are these problems?

Even further edit: For the version that was published locally, I found that this problem occurs when my App Pool runs under a built-in account (such as ApplicationPoolIdentity). However, it's fixed when I use a specific user account. However, this does not work on the server.

Post the full code, where do you make the call? How is the request? What headers? How is your controller? — Sxntk, Apr 21 '20 at 19:28
Do you mean that when you call the service from another client, for example Postman, you get a valid response, and have you added your iis website url to windows host file? — Aspram, Apr 21 '20 at 23:00
@Aspram I can call the API from multiple clients - I have a WPF application and a console application (both standard .NET, but the code is quite similar in both cases) that I use to call the endpoint regularly. I'm also able to call it when I'm running my web site by debugging in Visual Studio. Unfortunately, when I publish to IIS and run it that way, I get the error I mentioned in my question. — EJoshuaS - Stand with Ukraine, Apr 21 '20 at 23:10
Well, after that, only IIS configuration could be wrong, please show us how is the pool and the site is configured — Sxntk, Apr 22 '20 at 12:15
@Sxntk I updated with the modules. Is there any problem there, or am I looking at the wrong thing? — EJoshuaS - Stand with Ukraine, Apr 22 '20 at 13:52
I suggest remove "[Authorize(Roles = "CreateUser,PatchUser")]" and try againg, after that change the Managed pipeline mode to Classic and try again, as you can see, there is no clear why is failing ONLY when you deploy to IIS and make the request. — Sxntk, Apr 22 '20 at 14:04
@Sxntk I don't see why removing the authorization would help. That method gets called - it only fails when it does the web service call to an outside API. — EJoshuaS - Stand with Ukraine, Apr 22 '20 at 15:01
At a guess, there are a lot of IIS features in windows which aren't installed by default. If you haven't done so already, have a look in ***Turn Windows Features on or off*** in case there are any features which you think may be related. — Ben Cottrell, May 15 '20 at 20:48
Also make sure that IIS logs are enabled too so that you can see what's really happening with each request from the IIS logfile - https://learn.microsoft.com/en-us/iis/manage/provisioning-and-managing-iis/configure-logging-in-iis — Ben Cottrell, May 15 '20 at 20:54

EJoshuaS - Stand with Ukraine · Accepted Answer · 2020-05-16T01:27:21.820

It turns out that the requests being blocked by the corporate firewall. The server sits behind two firewalls, which is why changing the server's inbound or outbound rules didn't help me (because the other firewall was just blocking the call instead).

To resolve this, I needed to use a proxy server. I looked up the fully qualified name of the server in the appropriate documentation. In my Startup.cs, I added the following logic:

services.AddHttpClient("MyName", c =>
        {
            c.BaseAddress = new Uri("[Vendor API url]");

            c.Timeout = new TimeSpan(4, 0, 0);

            c.DefaultRequestHeaders.Accept.Clear();

            c.DefaultRequestHeaders.Add("Accept", "application/json");

            c.DefaultRequestHeaders.Add("ApiToken", RetrieveApiKey());
        })
            .ConfigurePrimaryHttpMessageHandler(() =>
            {
                return new HttpClientHandler()
                {
                    AllowAutoRedirect = true,
                    SslProtocols = SslProtocols.Tls13,
                    UseProxy = true,
                    Proxy = new WebProxy("ProxyServerName", 8080)
                    {
                        // The proxy server allows NTLM and Kerberos authentication
                        UseDefaultCredentials = true
                    }
                };
            });

"No such host is known" when publishing locally, but not when debugging in Visual Studio

1 Answers1