Fix Azure roles resources always redeploying

src/Aspire.Hosting.Azure/Provisioning/BicepUtilities.cs

@@ -14,17 +14,34 @@ namespace Aspire.Hosting.Azure.Provisioning;
 /// </summary>
 internal static class BicepUtilities
 {
+    // Known values since they will be filled in by the provisioner
+    private static readonly string[] s_knownParameterNames =
+    [
+        AzureBicepResource.KnownParameters.PrincipalName,
+        AzureBicepResource.KnownParameters.PrincipalId,
+        AzureBicepResource.KnownParameters.PrincipalType,
+        AzureBicepResource.KnownParameters.UserPrincipalId,
+        AzureBicepResource.KnownParameters.Location,
+    ];
+
     /// <summary>
     /// Converts the parameters to a JSON object compatible with the ARM template.
     /// </summary>
-    public static async Task SetParametersAsync(JsonObject parameters, AzureBicepResource resource, CancellationToken cancellationToken = default)
+    public static async Task SetParametersAsync(JsonObject parameters, AzureBicepResource resource, bool skipKnownValues = false, CancellationToken cancellationToken = default)
     {
         // Convert the parameters to a JSON object
         foreach (var parameter in resource.Parameters)
         {
             // Execute parameter values which are deferred.
             var parameterValue = parameter.Value is Func<object?> f ? f() : parameter.Value;
 
+            // Skip known parameters with 'null' values, like PrincipalType and PrincipalId, since they are filled in by the provisioner
+            // and are not available at this time. If we don't do this, the "roles" resources will be re-deployed every run.
+            if (skipKnownValues && s_knownParameterNames.Contains(parameter.Key) && parameterValue is null)
+            {
+                continue;
+            }
+
             parameters[parameter.Key] = new JsonObject()
             {
                 ["value"] = parameterValue switch
@@ -109,7 +126,7 @@ public static string GetChecksum(AzureBicepResource resource, JsonObject paramet
             _ = resource.GetBicepTemplateString();
 
             // Now overwrite with live object values skipping known values.
-            await SetParametersAsync(parameters, resource, cancellationToken: cancellationToken).ConfigureAwait(false);
+            await SetParametersAsync(parameters, resource, skipKnownValues: true, cancellationToken: cancellationToken).ConfigureAwait(false);
             if (scope is not null)
             {
                 await SetScopeAsync(scope, resource, cancellationToken).ConfigureAwait(false);
@@ -130,4 +147,4 @@ public static string GetChecksum(AzureBicepResource resource, JsonObject paramet
             (resource.TryGetLastAnnotation<ExistingAzureResourceAnnotation>(out var existingResource) ?
                 existingResource.ResourceGroup :
                 null);
-}
+}

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

@@ -428,11 +428,49 @@ public async Task GetCurrentChecksumAsync_ReturnsValidChecksumForValidParameters
         Assert.NotEmpty(result);
     }
 
+    /// <summary>
+    /// Ensures that known parameters are not overwritten when calculating the checksum.
+    /// This is important because if these known parameters are overwritten, it means the "roles"
+    /// resources will be redeployed every time the app is run.
+    /// </summary>
+    [Fact]
+    public async Task GetCurrentChecksumAsync_DoesNotOverwriteKnownParameters()
+    {
+        // Arrange
+        using var builder = TestDistributedApplicationBuilder.Create();
+        var bicep = builder.AddBicepTemplateString("test", "param name string").Resource;
+        bicep.Parameters[AzureBicepResource.KnownParameters.PrincipalType] = null;
+        bicep.Parameters[AzureBicepResource.KnownParameters.PrincipalId] = null;
+
+        var parameters = new JsonObject
+        {
+            [AzureBicepResource.KnownParameters.PrincipalType] = new JsonObject { ["value"] = "User" },
+            [AzureBicepResource.KnownParameters.PrincipalId] = new JsonObject { ["value"] = "1234" },
+        };
+
+        var configurationBuilder = new ConfigurationBuilder();
+        configurationBuilder.AddInMemoryCollection(new Dictionary<string, string?>
+        {
+            ["Parameters"] = parameters.ToJsonString()
+        });
+        var config = configurationBuilder.Build();
+
+        // Act
+        var result = await BicepUtilities.GetCurrentChecksumAsync(bicep, config);
+
+        // Assert
+        Assert.NotNull(result);
+
+        // verify the checksum is the same as using the config parameters directly
+        var expected = BicepUtilities.GetChecksum(bicep, parameters, scope: null);
+        Assert.Equal(expected, result);
+    }
+
     private sealed class ResourceWithConnectionString(string name, string connectionString) :
         Resource(name),
         IResourceWithConnectionString
     {
         public ReferenceExpression ConnectionStringExpression =>
            ReferenceExpression.Create($"{connectionString}");
     }
-}
+}