Do not set TargetPort to Port when IsProxying is also set

src/Aspire.Hosting/ApplicationModel/EndpointAnnotation.cs

@@ -44,7 +44,16 @@ public EndpointAnnotation(ProtocolType protocol, string? uriScheme = null, strin
         _transport = transport;
         Name = name;
         Port = port;
-        TargetPort = targetPort ?? port;
+
+        TargetPort = targetPort;
+
+        // If the target port was not explicitly set and the service is not being proxied,
+        // we can set the target port to the port.
+        if (TargetPort is null && !isProxied)
+        {
+            TargetPort = port;
+        }
+
         IsExternal = isExternal ?? false;
         IsProxied = isProxied;
     }

src/Aspire.Hosting/Dcp/ApplicationExecutor.cs

@@ -1692,7 +1692,7 @@ private void AddServicesProducedInfo(IResource modelResource, IAnnotationHolder
             {
                 if (sp.EndpointAnnotation.TargetPort is null)
                 {
-                    throw new InvalidOperationException($"The endpoint for container resource {modelResourceName} must specify the ContainerPort");
+                    throw new InvalidOperationException($"The endpoint for container resource '{modelResourceName}' must specify the TargetPort");
                 }
 
                 sp.DcpServiceProducerAnnotation.Port = sp.EndpointAnnotation.TargetPort;
@@ -1708,6 +1708,17 @@ private void AddServicesProducedInfo(IResource modelResource, IAnnotationHolder
                 // so we need to specify what the port is so DCP is aware of it.
                 sp.DcpServiceProducerAnnotation.Port = sp.EndpointAnnotation.Port;
             }
+            else
+            {
+                Debug.Assert(sp.EndpointAnnotation.IsProxied);
+
+                var ep = sp.EndpointAnnotation;
+                if (ep.TargetPort is int && ep.Port is int && ep.TargetPort == ep.Port)
+                {
+                    throw new InvalidOperationException(
+                        $"The endpoint for non-container resource '{modelResourceName}' requested a proxy ({nameof(ep.IsProxied)} is true). Non-container resources cannot be proxied when both {nameof(ep.TargetPort)} and {nameof(ep.Port)} are specified with the same value.");
+                }
+            }
 
             dcpResource.AnnotateAsObjectList(CustomResource.ServiceProducerAnnotation, sp.DcpServiceProducerAnnotation);
             appResource.ServicesProduced.Add(sp);

src/Aspire.Hosting/Publishing/ManifestPublishingContext.cs

@@ -278,14 +278,17 @@ public void WriteBindings(IResource resource)
                 Writer.WriteString("protocol", endpoint.Protocol.ToString().ToLowerInvariant());
                 Writer.WriteString("transport", endpoint.Transport);
 
-                int? targetPort = (resource, endpoint.UriScheme, endpoint.TargetPort) switch
+                int? targetPort = (resource, endpoint.UriScheme, endpoint.TargetPort, endpoint.Port) switch
                 {
                     // The port was specified so use it
-                    (_, _, int port) => port,
+                    (_, _, int target, _) => target,
 
-                    // Project resources get their default port from the deployment tool
+                    // Container resources get their default listening port from the exposed port.
+                    (ContainerResource, _, null, int port) => port,
+
+                    // Project resources get their default listening port from the deployment tool
                     // ideally we would default to a known port but we don't know it at this point
-                    (ProjectResource, var scheme, null) when scheme is "http" or "https" => null,
+                    (ProjectResource, var scheme, null, _) when scheme is "http" or "https" => null,
 
                     // Allocate a dynamic port
                     _ => PortAllocator.AllocatePort()