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Pass target platform to DCP for Dockerfile builds #16700

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Pass target platform to DCP for Dockerfile builds #16700

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8208c44
Pass target platform to DCP for Dockerfile builds
McDonaldSean May 2, 2026
b61de7e
Address review feedback
McDonaldSean May 2, 2026
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17 changes: 15 additions & 2 deletions src/Aspire.Hosting/Dcp/ContainerCreator.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@
using System.Net.Sockets;
using Aspire.Hosting.ApplicationModel;
using Aspire.Hosting.Dcp.Model;
using Aspire.Hosting.Publishing;
using Aspire.Hosting.Utils;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
Expand Down Expand Up @@ -260,7 +261,7 @@ private async Task BuildAndCreateContainerAsync(RenderedModelResource<Container>
var dcpContainer = cr.DcpResource;
var modelContainer = cr.ModelResource;

await ApplyBuildArgumentsAsync(dcpContainer, cr.ModelResource, _executionContext.ServiceProvider, cToken).ConfigureAwait(false);
await ApplyBuildArgumentsAsync(dcpContainer, cr.ModelResource, _executionContext.ServiceProvider, logger, cToken).ConfigureAwait(false);

var spec = dcpContainer.Spec;

Expand Down Expand Up @@ -732,7 +733,7 @@ await modelResource.ProcessContainerRuntimeArgValues(
return (runArgs, failedToApplyArgs);
}

private static async Task ApplyBuildArgumentsAsync(Container dcpContainerResource, IResource modelContainerResource, IServiceProvider serviceProvider, CancellationToken cancellationToken)
private static async Task ApplyBuildArgumentsAsync(Container dcpContainerResource, IResource modelContainerResource, IServiceProvider serviceProvider, ILogger logger, CancellationToken cancellationToken)
{
if (modelContainerResource.Annotations.OfType<DockerfileBuildAnnotation>().SingleOrDefault() is { } dockerfileBuildAnnotation)
{
Expand Down Expand Up @@ -783,6 +784,18 @@ private static async Task ApplyBuildArgumentsAsync(Container dcpContainerResourc
Args = dcpBuildArgs,
Secrets = dcpBuildSecrets
};

#pragma warning disable ASPIREPIPELINES003 // ContainerBuildOptions APIs are experimental.
var buildOptionsContext = await modelContainerResource.ProcessContainerBuildOptionsCallbackAsync(
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@danegsta danegsta May 2, 2026

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This would need to be done in a way that doesn't take a dependency on the publish types in DCP (no Aspire.Hosting.Publishing dependency).

serviceProvider,
logger,
cancellationToken: cancellationToken).ConfigureAwait(false);

if (buildOptionsContext.TargetPlatform is { } targetPlatform)
{
dcpContainerResource.Spec.Build.Platform = targetPlatform.ToRuntimePlatformString();
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@danegsta danegsta May 2, 2026

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I'm nervous about us overriding the default run time platform to linux/amd64 regardless of the host architecture at run time when building a Dockerfile just because I've seen enough cases where the emulation layers fail. I'd want to consider supporting separate publish and runtime defaults (stick with linux/amd64 as the default publish platform, but continue to use the current machine architecture as the default at runtime.

}
#pragma warning restore ASPIREPIPELINES003
}
}

Expand Down
4 changes: 4 additions & 0 deletions src/Aspire.Hosting/Dcp/Model/Container.cs
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Expand Up @@ -126,6 +126,10 @@ internal sealed class BuildContext
// Optional labels to apply to the built image
[JsonPropertyName("labels")]
public List<ContainerLabel>? Labels { get; set; }

// Optional target platform for the build (e.g. "linux/amd64")
[JsonPropertyName("platform")]
public string? Platform { get; set; }
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@danegsta danegsta May 2, 2026

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There isn't a platform field in the DCP types (https://github.com/microsoft/dcp/blob/main/api/v1/container_types.go#L140), so any proposed change would need to start there.

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@McDonaldSean McDonaldSean May 5, 2026

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Opened initial PR -> microsoft/dcp#140

}

internal sealed class BuildContextSecret
Expand Down
26 changes: 26 additions & 0 deletions tests/Aspire.Hosting.Tests/Dcp/DcpExecutorTests.cs
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Expand Up @@ -12,6 +12,7 @@
using Aspire.Dashboard.Model;
using Aspire.Hosting.Dcp;
using Aspire.Hosting.Dcp.Model;
using Aspire.Hosting.Publishing;
using Aspire.Hosting.Tests.Utils;
using k8s.Models;
using Microsoft.AspNetCore.InternalTesting;
Expand Down Expand Up @@ -51,6 +52,31 @@ public async Task ContainersArePassedOtelServiceName()
Assert.Equal("CustomName", container.Metadata.Annotations["otel-service-name"]);
}

[Fact]
public async Task DockerfileContainerBuildSpecIncludesPlatform()
{
using var tempDockerfileContext = await DockerfileUtils.CreateTemporaryDockerfileAsync();

var builder = DistributedApplication.CreateBuilder();
#pragma warning disable ASPIREPIPELINES003 // ContainerBuildOptions APIs are experimental.
builder.AddDockerfile("mycontainer", tempDockerfileContext.ContextPath, tempDockerfileContext.DockerfilePath)
.WithContainerBuildOptions(ctx => ctx.TargetPlatform = ContainerTargetPlatform.LinuxArm64);
#pragma warning restore ASPIREPIPELINES003

var kubernetesService = new TestKubernetesService();

using var app = builder.Build();
var distributedAppModel = app.Services.GetRequiredService<DistributedApplicationModel>();

var appExecutor = CreateAppExecutor(distributedAppModel, kubernetesService: kubernetesService);

await appExecutor.RunApplicationAsync();

var container = Assert.Single(kubernetesService.CreatedResources.OfType<Container>());
Assert.NotNull(container.Spec.Build);
Assert.Equal("linux/arm64", container.Spec.Build!.Platform);
}

[Fact]
public async Task ResourceStarted_ProjectHasReplicas_EventRaisedOnce()
{
Expand Down
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