ASP.NET Core MVC : static file response with prefix when using nginx ingress rewrite

Question

I'm not a .NET developer but gotta provide a sample ASP.NET Core Web App (Model-View-Controller) to a client. But I have a problem when deploying it onto Kubernetes.

For example, when I click Privacy button, I get 404 errors.

//ex.
// root
www.example.com/custom/path

// Desired
www.example.com/custom/path/Home/Privacy

// Actual - 404 error as ingress cannot route it.
www.example.com/Home/Privacy

Code

I'm using nginx-ingress for routing traffics.

The ingress looks like (using rewrite)

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  annotations:
    //...
    // I have to use rewrite
    nginx.ingress.kubernetes.io/rewrite-target: /$1
    //...

spec:
  ingressClassName: nginx
  rules:
    - host: www.example.com
      http:
        paths:
          - backend:
              service:
                name: dotnet-service
                port:
                  number: 8080
            path: /custom/path/?(.*)
            pathType: ImplementationSpecific

Program.cs

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddControllersWithViews();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Home/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.UseRouting();

app.UseAuthorization();

app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}");

app.Run();

Views/Shared/_Layout.cshtml

<!DOCTYPE html>
<html lang="en">
<head>
    @* Add below line for setting prefix for href in link tag *@
    <base href="/custom/path/">
    @* ... *@
    <link rel="stylesheet" href="lib/bootstrap/dist/css/bootstrap.min.css" />
    <link rel="stylesheet" href="css/site.css" asp-append-version="true" />
    <link rel="stylesheet" href="MVPPractice.styles.css" asp-append-version="true" />
</head>
<body>
    <header>
        <nav class="navbar navbar-expand-sm navbar-toggleable-sm navbar-light bg-white border-bottom box-shadow mb-3">
            <div class="container-fluid">
                <a class="navbar-brand" asp-area="" asp-controller="Home" asp-action="Index">MVPPractice</a>
                <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target=".navbar-collapse" aria-controls="navbarSupportedContent"
                        aria-expanded="false" aria-label="Toggle navigation">
                    <span class="navbar-toggler-icon"></span>
                </button>
                <div class="navbar-collapse collapse d-sm-inline-flex justify-content-between">
                    <ul class="navbar-nav flex-grow-1">
                        <li class="nav-item">
                            <a class="nav-link text-dark" asp-area="" asp-controller="Home" asp-action="Index">Home</a>
                        </li>
                        <li class="nav-item">
                            <a class="nav-link text-dark" asp-area="" asp-controller="Home" asp-action="Privacy">Privacy</a>
                        </li>
                    </ul>
                </div>
            </div>
        </nav>
    </header>

    @* ... *@

    <script src="lib/jquery/dist/jquery.min.js"></script>
    <script src="lib/bootstrap/dist/js/bootstrap.bundle.min.js"></script>
    <script src="js/site.js" asp-append-version="true"></script>
    @await RenderSectionAsync("Scripts", required: false)
</body>
</html>

Traffic flow

ASP.NET program's base is root(/) not /custom/path, that's why I use nginx-ingress's rewrite.

Current Issue

Request www.example.com/custom/path/

Response 200
href of <a> is /Home/Privacy which leads to www.example.com/Home/Privacy, it is supposed to be /custom/path/Home/Privacy so that it leads to www.example.com/custom/path/Home/Privacy.

Click the link <a>

Requests www.example.com/Home/Privacy
Response 404 (because nginx-ingress cannot route it)

How do I set prefix for static file responses?

Can you show us your program.cs file? You should have a line something like app.UseStaticFiles(); in there - do you? — marc_s
– marc_s, Commented Nov 25, 2024 at 15:31
@marc_s thx I'ved added Program.cs and _Layout.cshtml. I've got that line as I barely changed the code. — song2park
– song2park, Commented Nov 26, 2024 at 0:17
I suspect something is off with the url rewrite in the ingress. Can you see in the aspnet core logs what url is being requested from the app? — ESG
– ESG, Commented Nov 26, 2024 at 1:33
Make sure you read learn.microsoft.com/en-us/aspnet/core/host-and-deploy/… So long as your proxy sets X-Forwarded-Prefix and you configure the server to trust it, then everything should work without hard-coding anything. — Jeremy Lakeman
– Jeremy Lakeman, Commented Nov 26, 2024 at 4:31
@ESG No logs as nginx-ingress failed the route the request, it couldn't even reach asp.net program. The requested url need be based on root from dotnet's perspective. — song2park
– song2park, Commented Nov 26, 2024 at 4:32

Jalpa Panchal · Accepted Answer · 2024-11-26 02:53:04Z

0

You could try this below code to rewrite the url to your custom path to avoid the 404 error:

Program.cs:

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddControllersWithViews();
var app = builder.Build();

// Configure the application to use a base path
app.UsePathBase("/custom/path"); 

if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Home/Error");
    app.UseHsts();
}
app.UseHttpsRedirection();

app.UseStaticFiles();
app.UseRouting();
app.UseAuthorization();
app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}");
app.Run();

YAML:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: dotnet-ingress
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target: /custom/path/$1
    nginx.ingress.kubernetes.io/use-regex: "true"
spec:
  ingressClassName: nginx
  rules:
    - host: www.example.com
      http:
        paths:
          - path: /custom/path/?(.*)
            pathType: ImplementationSpecific
            backend:
              service:
                name: dotnet-service
                port:
                  number: 8080

If you only would like to serve the static file you could use the RequestPath something like below:

app.UseStaticFiles(new StaticFileOptions
{
    RequestPath = "/StaticFiles"
});

If you would like entire application, including routes, controllers, and static files use the path like /custom/path use app.UsePathBase("/custom/path");

answered Nov 26, 2024 at 2:53

Jalpa Panchal

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1 Comment

song2park Nov 26, 2024 at 4:29

The rewrite-target can't be changed as it is intended. Inside the container(ASP.NET), the base is root but outside the kubernetes, it's /custom/path (from user's perspective)

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