From 877592194b76ddfd472cde71e56f434fd73a8eb4 Mon Sep 17 00:00:00 2001
From: Lyndon-Li <lyonghui@vmware.com>
Date: Tue, 10 Oct 2023 11:04:04 +0800
Subject: [PATCH] issue 6734: spread backup pod evenly

Signed-off-by: Lyndon-Li <lyonghui@vmware.com>
---
 changelogs/unreleased/6935-Lyndon-Li |  1 +
 pkg/exposer/csi_snapshot.go          | 18 ++++++++++++++++++
 pkg/exposer/types.go                 |  2 ++
 3 files changed, 21 insertions(+)
 create mode 100644 changelogs/unreleased/6935-Lyndon-Li

diff --git a/changelogs/unreleased/6935-Lyndon-Li b/changelogs/unreleased/6935-Lyndon-Li
new file mode 100644
index 0000000000..b14c4f3cce
--- /dev/null
+++ b/changelogs/unreleased/6935-Lyndon-Li
@@ -0,0 +1 @@
+Partially fix #6734, guide Kubernetes' scheduler to spread backup pods evenly across nodes as much as possible, so that data mover backup could achieve better parallelism
\ No newline at end of file
diff --git a/pkg/exposer/csi_snapshot.go b/pkg/exposer/csi_snapshot.go
index a0492d5233..85f511524c 100644
--- a/pkg/exposer/csi_snapshot.go
+++ b/pkg/exposer/csi_snapshot.go
@@ -361,6 +361,12 @@ func (e *csiSnapshotExposer) createBackupPod(ctx context.Context, ownerObject co
 	var gracePeriod int64 = 0
 	volumeMounts, volumeDevices := kube.MakePodPVCAttachment(volumeName, backupPVC.Spec.VolumeMode)
 
+	if label == nil {
+		label = make(map[string]string)
+	}
+
+	label[podGroupLabel] = podGroupSnapshot
+
 	pod := &corev1.Pod{
 		ObjectMeta: metav1.ObjectMeta{
 			Name:      podName,
@@ -377,6 +383,18 @@ func (e *csiSnapshotExposer) createBackupPod(ctx context.Context, ownerObject co
 			Labels: label,
 		},
 		Spec: corev1.PodSpec{
+			TopologySpreadConstraints: []corev1.TopologySpreadConstraint{
+				{
+					MaxSkew:           1,
+					TopologyKey:       "kubernetes.io/hostname",
+					WhenUnsatisfiable: corev1.ScheduleAnyway,
+					LabelSelector: &metav1.LabelSelector{
+						MatchLabels: map[string]string{
+							podGroupLabel: podGroupSnapshot,
+						},
+					},
+				},
+			},
 			Containers: []corev1.Container{
 				{
 					Name:            containerName,
diff --git a/pkg/exposer/types.go b/pkg/exposer/types.go
index 21c473366d..f87620e8f8 100644
--- a/pkg/exposer/types.go
+++ b/pkg/exposer/types.go
@@ -23,6 +23,8 @@ import (
 const (
 	AccessModeFileSystem = "by-file-system"
 	AccessModeBlock      = "by-block-device"
+	podGroupLabel        = "velero.io/exposer-pod-group"
+	podGroupSnapshot     = "snapshot-exposer"
 )
 
 // ExposeResult defines the result of expose.