Allow Azure VNet subnet name to be a parameter

src/Aspire.Hosting.Azure.Kubernetes/AzureKubernetesEnvironmentExtensions.cs

@@ -5,6 +5,7 @@
 #pragma warning disable ASPIREAZURE001 // AzureEnvironmentResource.ProvisionInfrastructureStepName for pipeline ordering
 #pragma warning disable ASPIREAZURE003 // AzureSubnetResource used in WithSubnet extensions
 
+using System.Diagnostics;
 using Aspire.Hosting.ApplicationModel;
 using Aspire.Hosting.Azure;
 using Aspire.Hosting.Azure.Kubernetes;
@@ -763,7 +764,20 @@ private static void ConfigureAksInfrastructure(AzureResourceInfrastructure infra
                 {
                     existingSubnet = SubnetResource.FromExisting(subnetIdentifier);
                     existingSubnet.Parent = existingVnet;
-                    existingSubnet.Name = subnet.SubnetName;
+
+                    if (subnet.SubnetName is not null)
+                    {
+                        existingSubnet.Name = subnet.SubnetName;
+                    }
+                    else if (subnet.SubnetNameParameter is not null)
+                    {
+                        existingSubnet.Name = subnet.SubnetNameParameter.AsProvisioningParameter(infrastructure);
+                    }
+                    else
+                    {
+                        throw new UnreachableException("Subnet name must be set.");
+                    }
+
                     infrastructure.Add(existingSubnet);
                     subnetExistingByKey[subnetIdentifier] = existingSubnet;
                 }

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

@@ -22,6 +22,7 @@ namespace Aspire.Hosting.Azure;
 public class AzureSubnetResource : Resource, IResourceWithParent<AzureVirtualNetworkResource>
 {
     // Backing field holds either string or ParameterResource
+    private readonly object _subnetName;
     private readonly object _addressPrefix;
 
     /// <summary>
@@ -34,7 +35,7 @@ public class AzureSubnetResource : Resource, IResourceWithParent<AzureVirtualNet
     public AzureSubnetResource(string name, string subnetName, string addressPrefix, AzureVirtualNetworkResource parent)
         : base(name)
     {
-        SubnetName = ThrowIfNullOrEmpty(subnetName);
+        _subnetName = ThrowIfNullOrEmpty(subnetName);
         _addressPrefix = ThrowIfNullOrEmpty(addressPrefix);
         Parent = parent ?? throw new ArgumentNullException(nameof(parent));
     }
@@ -49,21 +50,41 @@ public AzureSubnetResource(string name, string subnetName, string addressPrefix,
     public AzureSubnetResource(string name, string subnetName, ParameterResource addressPrefix, AzureVirtualNetworkResource parent)
         : base(name)
     {
-        SubnetName = ThrowIfNullOrEmpty(subnetName);
+        _subnetName = ThrowIfNullOrEmpty(subnetName);
         _addressPrefix = addressPrefix ?? throw new ArgumentNullException(nameof(addressPrefix));
         Parent = parent ?? throw new ArgumentNullException(nameof(parent));
     }
 
     /// <summary>
-    /// Gets the subnet name.
+    /// Initializes a new instance of the <see cref="AzureSubnetResource"/> class with parameterized subnet name and address prefix.
     /// </summary>
-    public string SubnetName { get; }
+    /// <param name="name">The name of the resource.</param>
+    /// <param name="subnetName">The parameter resource containing 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, ParameterResource subnetName, ParameterResource addressPrefix, AzureVirtualNetworkResource parent)
+        : base(name)
+    {
+        _subnetName = subnetName ?? throw new ArgumentNullException(nameof(subnetName));
+        _addressPrefix = addressPrefix ?? throw new ArgumentNullException(nameof(addressPrefix));
+        Parent = parent ?? throw new ArgumentNullException(nameof(parent));
+    }
+
+    /// <summary>
+    /// Gets the subnet name, or <c>null</c> if the subnet name is provided via a <see cref="ParameterResource"/>.
+    /// </summary>
+    public string? SubnetName => _subnetName as string;
 
     /// <summary>
     /// 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 => _addressPrefix as string;
 
+    /// <summary>
+    /// Gets the parameter resource containing the subnet name, or <c>null</c> if the subnet name is provided as a literal string.
+    /// </summary>
+    public ParameterResource? SubnetNameParameter => _subnetName as ParameterResource;
+
     /// <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>
@@ -97,10 +118,21 @@ private static string ThrowIfNullOrEmpty([NotNull] string? argument, [CallerArgu
     /// </summary>
     internal SubnetResource ToProvisioningEntity(AzureResourceInfrastructure infra, ProvisionableResource? dependsOn)
     {
-        var subnet = new SubnetResource(Infrastructure.NormalizeBicepIdentifier(Name))
+        var subnet = new SubnetResource(Infrastructure.NormalizeBicepIdentifier(Name));
+
+        // Set the subnet name from either the literal string or the parameter
+        if (_subnetName is string subnetName)
+        {
+            subnet.Name = subnetName;
+        }
+        else if (_subnetName is ParameterResource subnetNameParameter)
         {
-            Name = SubnetName,
-        };
+            subnet.Name = subnetNameParameter.AsProvisioningParameter(infra);
+        }
+        else
+        {
+            throw new UnreachableException("SubnetName must be set either as a string or a ParameterResource.");
+        }
 
         // Set the address prefix from either the literal string or the parameter
         if (_addressPrefix is string addressPrefix)

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

@@ -239,6 +239,40 @@ public static IResourceBuilder<AzureSubnetResource> AddSubnet(
         return AddSubnetCore(builder, subnet);
     }
 
+    /// <summary>
+    /// Adds an Azure Subnet to the Virtual Network with parameterized address prefix and subnet name.
+    /// </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 parameter resource containing the subnet name in Azure.</param>
+    /// <returns>A reference to the <see cref="IResourceBuilder{AzureSubnetResource}"/>.</returns>
+    /// <example>
+    /// This example adds a subnet with parameterized address prefix and subnet name:
+    /// <code>
+    /// var subnetName = builder.AddParameter("subnetName");
+    /// var subnetPrefix = builder.AddParameter("subnetPrefix");
+    /// var vnet = builder.AddAzureVirtualNetwork("vnet");
+    /// var subnet = vnet.AddSubnet("my-subnet", subnetPrefix, subnetName);
+    /// </code>
+    /// </example>
+    [AspireExportIgnore(Reason = "Polyglot app hosts use the internal addSubnet dispatcher export.")]
+    public static IResourceBuilder<AzureSubnetResource> AddSubnet(
+        this IResourceBuilder<AzureVirtualNetworkResource> builder,
+        [ResourceName] string name,
+        IResourceBuilder<ParameterResource> addressPrefix,
+        IResourceBuilder<ParameterResource> subnetName)
+    {
+        ArgumentNullException.ThrowIfNull(builder);
+        ArgumentException.ThrowIfNullOrEmpty(name);
+        ArgumentNullException.ThrowIfNull(addressPrefix);
+        ArgumentNullException.ThrowIfNull(subnetName);
+
+        var subnet = new AzureSubnetResource(name, subnetName.Resource, addressPrefix.Resource, builder.Resource);
+
+        return AddSubnetCore(builder, subnet);
+    }
+
     /// <summary>
     /// Adds an Azure subnet resource to an Azure Virtual Network resource.
     /// </summary>