Allow subnet addressprefix to be a parameter.

src/Aspire.Hosting.Azure.Network/AzureSubnetResource.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using Aspire.Hosting.ApplicationModel;
@@ -13,35 +14,68 @@ namespace Aspire.Hosting.Azure;
 /// <summary>
 /// Represents an Azure Subnet resource.
 /// </summary>
-/// <param name="name">The name of the resource.</param>
-/// <param name="subnetName">The subnet name.</param>
-/// <param name="addressPrefix">The address prefix for the subnet.</param>
-/// <param name="parent">The parent Virtual Network resource.</param>
 /// <remarks>
 /// Use <see cref="AzureProvisioningResourceExtensions.ConfigureInfrastructure{T}(ApplicationModel.IResourceBuilder{T}, Action{AzureResourceInfrastructure})"/> to configure specific <see cref="Azure.Provisioning"/> properties.
 /// </remarks>
-public class AzureSubnetResource(string name, string subnetName, string addressPrefix, AzureVirtualNetworkResource parent)
-    : Resource(name), IResourceWithParent<AzureVirtualNetworkResource>
+public class AzureSubnetResource : Resource, IResourceWithParent<AzureVirtualNetworkResource>
 {
+    // Backing field holds either string or ParameterResource
+    private readonly object _addressPrefix;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="AzureSubnetResource"/> class.
+    /// </summary>
+    /// <param name="name">The name of the resource.</param>
+    /// <param name="subnetName">The subnet name.</param>
+    /// <param name="addressPrefix">The address prefix for the subnet.</param>
+    /// <param name="parent">The parent Virtual Network resource.</param>
+    public AzureSubnetResource(string name, string subnetName, string addressPrefix, AzureVirtualNetworkResource parent)
+        : base(name)
+    {
+        SubnetName = ThrowIfNullOrEmpty(subnetName);
+        _addressPrefix = ThrowIfNullOrEmpty(addressPrefix);
+        Parent = parent ?? throw new ArgumentNullException(nameof(parent));
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="AzureSubnetResource"/> class with a parameterized address prefix.
+    /// </summary>
+    /// <param name="name">The name of the resource.</param>
+    /// <param name="subnetName">The subnet name.</param>
+    /// <param name="addressPrefix">The parameter resource containing the address prefix for the subnet.</param>
+    /// <param name="parent">The parent Virtual Network resource.</param>
+    public AzureSubnetResource(string name, string subnetName, ParameterResource addressPrefix, AzureVirtualNetworkResource parent)
+        : base(name)
+    {
+        SubnetName = ThrowIfNullOrEmpty(subnetName);
+        _addressPrefix = addressPrefix ?? throw new ArgumentNullException(nameof(addressPrefix));
+        Parent = parent ?? throw new ArgumentNullException(nameof(parent));
+    }
+
     /// <summary>
     /// Gets the subnet name.
     /// </summary>
-    public string SubnetName { get; } = ThrowIfNullOrEmpty(subnetName);
+    public string SubnetName { get; }
 
     /// <summary>
-    /// Gets the address prefix for the subnet (e.g., "10.0.1.0/24").
+    /// Gets the address prefix for the subnet (e.g., "10.0.1.0/24"), or <c>null</c> if the address prefix is provided via a <see cref="ParameterResource"/>.
     /// </summary>
-    public string AddressPrefix { get; } = ThrowIfNullOrEmpty(addressPrefix);
+    public string? AddressPrefix => _addressPrefix as string;
+
+    /// <summary>
+    /// Gets the parameter resource containing the address prefix for the subnet, or <c>null</c> if the address prefix is provided as a literal string.
+    /// </summary>
+    public ParameterResource? AddressPrefixParameter => _addressPrefix as ParameterResource;
 
     /// <summary>
     /// Gets the subnet Id output reference.
     /// </summary>
-    public BicepOutputReference Id => new($"{Infrastructure.NormalizeBicepIdentifier(Name)}_Id", parent);
+    public BicepOutputReference Id => new($"{Infrastructure.NormalizeBicepIdentifier(Name)}_Id", Parent);
 
     /// <summary>
     /// Gets the parent Azure Virtual Network resource.
     /// </summary>
-    public AzureVirtualNetworkResource Parent { get; } = parent ?? throw new ArgumentNullException(nameof(parent));
+    public AzureVirtualNetworkResource Parent { get; }
 
     private static string ThrowIfNullOrEmpty([NotNull] string? argument, [CallerArgumentExpression(nameof(argument))] string? paramName = null)
         => !string.IsNullOrEmpty(argument) ? argument : throw new ArgumentNullException(paramName);
@@ -54,9 +88,22 @@ internal SubnetResource ToProvisioningEntity(AzureResourceInfrastructure infra,
         var subnet = new SubnetResource(Infrastructure.NormalizeBicepIdentifier(Name))
         {
             Name = SubnetName,
-            AddressPrefix = AddressPrefix,
         };
 
+        // Set the address prefix from either the literal string or the parameter
+        if (_addressPrefix is string addressPrefix)
+        {
+            subnet.AddressPrefix = addressPrefix;
+        }
+        else if (_addressPrefix is ParameterResource addressPrefixParameter)
+        {
+            subnet.AddressPrefix = addressPrefixParameter.AsProvisioningParameter(infra);
+        }
+        else
+        {
+            throw new UnreachableException("AddressPrefix must be set either as a string or a ParameterResource.");
+        }
+
         if (dependsOn is not null)
         {
             subnet.DependsOn.Add(dependsOn);

src/Aspire.Hosting.Azure.Network/AzureVirtualNetworkExtensions.cs

@@ -129,6 +129,46 @@ public static IResourceBuilder<AzureSubnetResource> AddSubnet(
 
         var subnet = new AzureSubnetResource(name, subnetName, addressPrefix, builder.Resource);
 
+        return AddSubnetCore(builder, subnet);
+    }
+
+    /// <summary>
+    /// Adds an Azure Subnet to the Virtual Network with a parameterized address prefix.
+    /// </summary>
+    /// <param name="builder">The Virtual Network resource builder.</param>
+    /// <param name="name">The name of the subnet resource.</param>
+    /// <param name="addressPrefix">The parameter resource containing the address prefix for the subnet (e.g., "10.0.1.0/24").</param>
+    /// <param name="subnetName">The subnet name in Azure. If null, the resource name is used.</param>
+    /// <returns>A reference to the <see cref="IResourceBuilder{AzureSubnetResource}"/>.</returns>
+    /// <example>
+    /// This example adds a subnet with a parameterized address prefix:
+    /// <code>
+    /// var subnetPrefix = builder.AddParameter("subnetPrefix");
+    /// var vnet = builder.AddAzureVirtualNetwork("vnet");
+    /// var subnet = vnet.AddSubnet("my-subnet", subnetPrefix);
+    /// </code>
+    /// </example>
+    public static IResourceBuilder<AzureSubnetResource> AddSubnet(
+        this IResourceBuilder<AzureVirtualNetworkResource> builder,
+        [ResourceName] string name,
+        IResourceBuilder<ParameterResource> addressPrefix,
+        string? subnetName = null)
+    {
+        ArgumentNullException.ThrowIfNull(builder);
+        ArgumentException.ThrowIfNullOrEmpty(name);
+        ArgumentNullException.ThrowIfNull(addressPrefix);
+
+        subnetName ??= name;
+
+        var subnet = new AzureSubnetResource(name, subnetName, addressPrefix.Resource, builder.Resource);
+
+        return AddSubnetCore(builder, subnet);
+    }
+
+    private static IResourceBuilder<AzureSubnetResource> AddSubnetCore(
+        IResourceBuilder<AzureVirtualNetworkResource> builder,
+        AzureSubnetResource subnet)
+    {
         builder.Resource.Subnets.Add(subnet);
 
         if (builder.ApplicationBuilder.ExecutionContext.IsRunMode)

tests/Aspire.Hosting.Azure.Tests/AzureVirtualNetworkExtensionsTests.cs

@@ -126,4 +126,50 @@ public void WithDelegatedSubnet_AddsAnnotationsToSubnetAndTarget()
         Assert.NotNull(delegationAnnotation);
         Assert.Equal("Microsoft.App/environments", delegationAnnotation.ServiceName);
     }
+
+    [Fact]
+    public void AddSubnet_WithParameterResource_CreatesSubnetResource()
+    {
+        using var builder = TestDistributedApplicationBuilder.Create(DistributedApplicationOperation.Publish);
+
+        var addressPrefixParam = builder.AddParameter("subnetPrefix");
+        var vnet = builder.AddAzureVirtualNetwork("myvnet");
+        var subnet = vnet.AddSubnet("mysubnet", addressPrefixParam);
+
+        Assert.NotNull(subnet);
+        Assert.Equal("mysubnet", subnet.Resource.Name);
+        Assert.Equal("mysubnet", subnet.Resource.SubnetName);
+        Assert.Null(subnet.Resource.AddressPrefix);
+        Assert.Same(addressPrefixParam.Resource, subnet.Resource.AddressPrefixParameter);
+        Assert.Same(vnet.Resource, subnet.Resource.Parent);
+    }
+
+    [Fact]
+    public void AddSubnet_WithParameterResource_AndCustomSubnetName()
+    {
+        using var builder = TestDistributedApplicationBuilder.Create(DistributedApplicationOperation.Publish);
+
+        var addressPrefixParam = builder.AddParameter("subnetPrefix");
+        var vnet = builder.AddAzureVirtualNetwork("myvnet");
+        var subnet = vnet.AddSubnet("mysubnet", addressPrefixParam, subnetName: "custom-subnet-name");
+
+        Assert.Equal("mysubnet", subnet.Resource.Name);
+        Assert.Equal("custom-subnet-name", subnet.Resource.SubnetName);
+        Assert.Null(subnet.Resource.AddressPrefix);
+        Assert.Same(addressPrefixParam.Resource, subnet.Resource.AddressPrefixParameter);
+    }
+
+    [Fact]
+    public async Task AddSubnet_WithParameterResource_GeneratesBicep()
+    {
+        using var builder = TestDistributedApplicationBuilder.Create(DistributedApplicationOperation.Publish);
+
+        var addressPrefixParam = builder.AddParameter("subnetPrefix");
+        var vnet = builder.AddAzureVirtualNetwork("myvnet");
+        vnet.AddSubnet("mysubnet", addressPrefixParam);
+
+        var manifest = await AzureManifestUtils.GetManifestWithBicep(vnet.Resource);
+
+        await Verify(manifest.BicepText, extension: "bicep");
+    }
 }

tests/Aspire.Hosting.Azure.Tests/Snapshots/AzureVirtualNetworkExtensionsTests.AddSubnet_WithParameterResource_GeneratesBicep.verified.bicep

@@ -0,0 +1,33 @@
+@description('The location for the resource(s) to be deployed.')
+param location string = resourceGroup().location
+
+param subnetPrefix string
+
+resource myvnet 'Microsoft.Network/virtualNetworks@2025-05-01' = {
+  name: take('myvnet-${uniqueString(resourceGroup().id)}', 64)
+  properties: {
+    addressSpace: {
+      addressPrefixes: [
+        '10.0.0.0/16'
+      ]
+    }
+  }
+  location: location
+  tags: {
+    'aspire-resource-name': 'myvnet'
+  }
+}
+
+resource mysubnet 'Microsoft.Network/virtualNetworks/subnets@2025-05-01' = {
+  name: 'mysubnet'
+  properties: {
+    addressPrefix: subnetPrefix
+  }
+  parent: myvnet
+}
+
+output mysubnet_Id string = mysubnet.id
+
+output id string = myvnet.id
+
+output name string = myvnet.name