From c42a416af0105d6b048428790f7855ca3d4a65d0 Mon Sep 17 00:00:00 2001
From: Rahul Raj <rahurja@amazon.com>
Date: Fri, 6 Mar 2026 10:47:55 +0000
Subject: [PATCH] Fix EFA interface count for instances where
 MaximumNetworkCards exceeds EFA limit

---
 pkg/cfn/builder/network_interfaces.go      |  6 ++-
 pkg/cfn/builder/network_interfaces_test.go | 44 ++++++++++++++++++++++
 2 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/pkg/cfn/builder/network_interfaces.go b/pkg/cfn/builder/network_interfaces.go
index 21805511da..3f95d4ae24 100644
--- a/pkg/cfn/builder/network_interfaces.go
+++ b/pkg/cfn/builder/network_interfaces.go
@@ -51,10 +51,14 @@ func buildNetworkInterfaces(
 		var numEFAs = math.MaxFloat64
 		for _, it := range info.InstanceTypes {
 			networkInfo := it.NetworkInfo
-			numEFAs = math.Min(float64(aws.ToInt32(networkInfo.MaximumNetworkCards)), numEFAs)
 			if !aws.ToBool(networkInfo.EfaSupported) {
 				return fmt.Errorf("instance type %s does not support EFA", it.InstanceType)
 			}
+			if networkInfo.EfaInfo != nil && networkInfo.EfaInfo.MaximumEfaInterfaces != nil {
+				numEFAs = math.Min(float64(aws.ToInt32(networkInfo.EfaInfo.MaximumEfaInterfaces)), numEFAs)
+			} else {
+				numEFAs = math.Min(float64(aws.ToInt32(networkInfo.MaximumNetworkCards)), numEFAs)
+			}
 		}
 
 		firstNI.InterfaceType = gfnt.NewString("efa")
diff --git a/pkg/cfn/builder/network_interfaces_test.go b/pkg/cfn/builder/network_interfaces_test.go
index fa2a791c25..7462d2da4a 100644
--- a/pkg/cfn/builder/network_interfaces_test.go
+++ b/pkg/cfn/builder/network_interfaces_test.go
@@ -142,6 +142,50 @@ func TestBuildNetworkInterfaces(t *testing.T) {
 			expectedNetworkInterfaces: 4,
 			expectedInterfaceType:     "efa",
 		},
+		{
+			name:          "EFA nodegroup with MaximumEfaInterfaces less than MaximumNetworkCards",
+			instanceTypes: []string{"p6-b300.48xlarge"},
+			efaEnabled:    true,
+			securityGroups: []*gfnt.Value{
+				gfnt.NewString("sg-12345"),
+			},
+			mockInstanceTypes: []ec2types.InstanceTypeInfo{
+				{
+					InstanceType: "p6-b300.48xlarge",
+					NetworkInfo: &ec2types.NetworkInfo{
+						MaximumNetworkCards: aws.Int32(17),
+						EfaSupported:        aws.Bool(true),
+						EfaInfo: &ec2types.EfaInfo{
+							MaximumEfaInterfaces: aws.Int32(8),
+						},
+					},
+				},
+			},
+			expectedNetworkInterfaces: 8,
+			expectedInterfaceType:     "efa",
+		},
+		{
+			name:          "EFA nodegroup with EfaInfo present and matching MaximumNetworkCards",
+			instanceTypes: []string{"p5.48xlarge"},
+			efaEnabled:    true,
+			securityGroups: []*gfnt.Value{
+				gfnt.NewString("sg-12345"),
+			},
+			mockInstanceTypes: []ec2types.InstanceTypeInfo{
+				{
+					InstanceType: "p5.48xlarge",
+					NetworkInfo: &ec2types.NetworkInfo{
+						MaximumNetworkCards: aws.Int32(32),
+						EfaSupported:        aws.Bool(true),
+						EfaInfo: &ec2types.EfaInfo{
+							MaximumEfaInterfaces: aws.Int32(32),
+						},
+					},
+				},
+			},
+			expectedNetworkInterfaces: 32,
+			expectedInterfaceType:     "efa",
+		},
 		{
 			name:          "EFA nodegroup with custom EFA security groups (1.32 scenario)",
 			instanceTypes: []string{"c5n.18xlarge"},