Blazor doesn't work in a Docker container

Question

I have an ASP.NET Core 8.0 MVC (upgraded from .NET 6.0) project; it's working fine in a Docker container except for the pages that contain Blazor code. I'm getting an error

blazor.server.js:1 [2025-04-01T04:53:37.291Z] Error: System.Net.Http.HttpRequestException: Connection refused (localhost:32784)

After investigation, I found that HttpRequest in .razor page was causing the issue.

protected async override void OnInitialized()
{
    var request = new HttpRequestMessage(HttpMethod.Get, uri);
    var response = await client.SendAsync(request);
}

Program.cs:

builder.Services.AddServerSideBlazor().AddCircuitOptions(options => { options.DetailedErrors = true; });

builder.Services.AddControllersWithViews();

builder.Services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();

builder.Services.AddDistributedMemoryCache();

builder.Services.AddHttpClient();

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    app.UseDeveloperExceptionPage();
    app.UseMigrationsEndPoint();
}
else
{
    app.UseExceptionHandler("/Home/Error");
    app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseRouting();

app.UseAuthentication();
app.UseAuthorization();

app.UseSession();

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

app.MapRazorPages();

app.MapBlazorHub();

.csproj:

<PackageReference Include="HtmlAgilityPack" Version="1.11.43" />
<PackageReference Include="Microsoft.AspNetCore.Components.WebAssembly.Server" Version="8.0.14" />
<PackageReference Include="Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore" Version="8.0.14" />
<PackageReference Include="Microsoft.AspNetCore.Identity.EntityFrameworkCore" Version="8.0.14" />
<PackageReference Include="Microsoft.AspNetCore.Identity.UI" Version="8.0.14" />
<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="8.0.14" />
<PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="8.0.14">
  <PrivateAssets>all</PrivateAssets>
  <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
</PackageReference>
<PackageReference Include="Microsoft.VisualStudio.Azure.Containers.Tools.Targets" Version="1.21.0" />
<PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="8.0.7" />
<PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
<PackageReference Include="System.Linq.Dynamic.Core" Version="1.2.19" />

Hi msd, does your problem only occur in docker? I tested it and vs2022 can also reproduce the problem. — buymeacoffee
– buymeacoffee, Commented Apr 1 at 4:18
After analyzing your scenario, I think you want to reload the page to reconnect after the websocket is disconnected. So I don't think your current solution is appropriate. Imagine that your website user is filling in the form information. When the websocket is disconnected, the page is reloaded, which is very unfriendly. — buymeacoffee
– buymeacoffee, Commented Apr 1 at 4:21
I honestly don’t remember why there’s a reload. As I recall, I just copied this code. Fortunately, the page doesn’t include any input; it only displays text and a few buttons. — msd
– msd, Commented Apr 1 at 4:31
Wait a minute, I just discovered that this error occurs regardless of whether I run it in Docker or not. It seems unrelated to the issue. However, a new error has occurred only in Docker. My bad, I will edit my question now. — msd
– msd, Commented Apr 1 at 5:00

buymeacoffee · Accepted Answer · 2025-04-01 06:45:01Z

1

We can find the issue is related to the httpclient from the error message.

System.Net.Http.HttpRequestException: Connection refused (localhost:32784)

We can fix it by using configurations like below.

builder.Services.AddHttpClient("MyClient", client =>
{
    // you can use host.docker.internal in docker environment
    client.BaseAddress = new Uri("http://host.docker.internal:your_port/");
    // or use below setting according to our needs
    // client.BaseAddress = new Uri("http://api-service:8080/");
});

answered Apr 1 at 6:45

buymeacoffee

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msd · Accepted Answer · 2025-04-01 06:32:54Z

0

I found it! It turns out I wasn’t using the Docker ports (EXPOSE 8080, EXPOSE 8081) in the HttpRequest URI.

answered Apr 1 at 6:32

msd

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