feat(plugin): DC/rack/node filtering for volume balance (#8621)

* feat(plugin): add DC/rack/node filtering for volume balance detection

Add scoping filters so balance detection can be limited to specific data
centers, racks, or nodes. Filters are applied both at the metrics level
(in the handler) and at the topology seeding level (in detection) to
ensure only the targeted infrastructure participates in balancing.

* address PR review: use set lookups, deduplicate test helpers, add target checks

* address review: assert non-empty tasks in filter tests

Prevent vacuous test passes by requiring len(tasks) > 0
before checking source/target exclusions.

* address review: enforce filter scope in fallback, clarify DC filter

- Thread allowedServers into createBalanceTask so the fallback
  planner cannot produce out-of-scope targets when DC/rack/node
  filters are active
- Update data_center_filter description to clarify single-DC usage

* address review: centralize parseCSVSet, fix filter scope leak, iterate all targets

- Extract ParseCSVSet to shared weed/worker/tasks/util package,
  remove duplicates from detection.go and volume_balance_handler.go
- Fix metric accumulation re-introducing filtered-out servers by
  only counting metrics for servers that passed DC/rack/node filters
- Trim DataCenterFilter before matching to handle trailing spaces
- Iterate all task.TypedParams.Targets in filter tests, not just [0]

* remove useless descriptor string test

weed/worker/tasks/balance/config.go

@@ -14,6 +14,9 @@ type Config struct {
 	base.BaseConfig
 	ImbalanceThreshold float64 `json:"imbalance_threshold"`
 	MinServerCount     int     `json:"min_server_count"`
+	DataCenterFilter   string  `json:"-"` // per-detection-run, not persisted
+	RackFilter         string  `json:"-"` // per-detection-run, not persisted
+	NodeFilter         string  `json:"-"` // per-detection-run, not persisted
 }
 
 // NewDefaultConfig creates a new default balance configuration

weed/worker/tasks/balance/detection.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"math"
 	"sort"
+	"strings"
 	"time"
 
 	"github.com/seaweedfs/seaweedfs/weed/admin/topology"
@@ -86,9 +87,21 @@ func detectForDiskType(diskType string, diskMetrics []*types.VolumeHealthMetrics
 	if clusterInfo.ActiveTopology != nil {
 		topologyInfo := clusterInfo.ActiveTopology.GetTopologyInfo()
 		if topologyInfo != nil {
+			rackFilterSet := util.ParseCSVSet(balanceConfig.RackFilter)
+			nodeFilterSet := util.ParseCSVSet(balanceConfig.NodeFilter)
+			dcFilter := strings.TrimSpace(balanceConfig.DataCenterFilter)
 			for _, dc := range topologyInfo.DataCenterInfos {
+				if dcFilter != "" && dc.Id != dcFilter {
+					continue
+				}
 				for _, rack := range dc.RackInfos {
+					if rackFilterSet != nil && !rackFilterSet[rack.Id] {
+						continue
+					}
 					for _, node := range rack.DataNodeInfos {
+						if nodeFilterSet != nil && !nodeFilterSet[node.Id] {
+							continue
+						}
 						for diskTypeName, diskInfo := range node.DiskInfos {
 							if diskTypeName == diskType {
 								serverVolumeCounts[node.Id] = 0
@@ -100,7 +113,15 @@ func detectForDiskType(diskType string, diskMetrics []*types.VolumeHealthMetrics
 			}
 		}
 	}
+	hasLocationFilter := balanceConfig.DataCenterFilter != "" || balanceConfig.RackFilter != "" || balanceConfig.NodeFilter != ""
 	for _, metric := range diskMetrics {
+		if hasLocationFilter {
+			// Only count metrics for servers that passed filtering.
+			// Without this guard, out-of-scope servers are re-introduced.
+			if _, allowed := serverVolumeCounts[metric.Server]; !allowed {
+				continue
+			}
+		}
 		serverVolumeCounts[metric.Server]++
 	}
 
@@ -285,7 +306,7 @@ func detectForDiskType(diskType string, diskMetrics []*types.VolumeHealthMetrics
 		// and the destination selection stay in sync. Without this, the topology's
 		// LoadCount-based scoring can diverge from the adjustment-based effective
 		// counts, causing moves to pile onto one server or oscillate (A→B, B→A).
-		task, destServerID := createBalanceTask(diskType, selectedVolume, clusterInfo, minServer)
+		task, destServerID := createBalanceTask(diskType, selectedVolume, clusterInfo, minServer, serverVolumeCounts)
 		if task == nil {
 			glog.V(1).Infof("BALANCE [%s]: Cannot plan task for volume %d on server %s, trying next volume", diskType, selectedVolume.VolumeID, maxServer)
 			continue
@@ -317,7 +338,10 @@ func detectForDiskType(diskType string, diskMetrics []*types.VolumeHealthMetrics
 // targetServer is the server ID chosen by the detection loop's greedy algorithm.
 // Returns (nil, "") if destination planning fails.
 // On success, returns the task result and the canonical destination server ID.
-func createBalanceTask(diskType string, selectedVolume *types.VolumeHealthMetrics, clusterInfo *types.ClusterInfo, targetServer string) (*types.TaskDetectionResult, string) {
+// allowedServers is the set of servers that passed DC/rack/node filtering in
+// the detection loop. When non-empty, the fallback destination planner is
+// checked against this set so that filter scope cannot leak.
+func createBalanceTask(diskType string, selectedVolume *types.VolumeHealthMetrics, clusterInfo *types.ClusterInfo, targetServer string, allowedServers map[string]int) (*types.TaskDetectionResult, string) {
 	taskID := fmt.Sprintf("balance_vol_%d_%d", selectedVolume.VolumeID, time.Now().UnixNano())
 
 	task := &types.TaskDetectionResult{
@@ -353,6 +377,18 @@ func createBalanceTask(diskType string, selectedVolume *types.VolumeHealthMetric
 		}
 	}
 
+	// Verify the destination is within the filtered scope. When DC/rack/node
+	// filters are active, allowedServers contains only the servers that passed
+	// filtering. The fallback planner queries the full topology, so this check
+	// prevents out-of-scope targets from leaking through.
+	if len(allowedServers) > 0 {
+		if _, ok := allowedServers[destinationPlan.TargetNode]; !ok {
+			glog.V(1).Infof("BALANCE [%s]: Planned destination %s for volume %d is outside filtered scope, skipping",
+				diskType, destinationPlan.TargetNode, selectedVolume.VolumeID)
+			return nil, ""
+		}
+	}
+
 	// Find the actual disk containing the volume on the source server
 	sourceDisk, found := base.FindVolumeDisk(clusterInfo.ActiveTopology, selectedVolume.VolumeID, selectedVolume.Collection, selectedVolume.Server)
 	if !found {
@@ -587,3 +623,5 @@ func calculateBalanceScore(disk *topology.DiskInfo, sourceRack, sourceDC string,
 
 	return score
 }
+
+// parseCSVSet splits a comma-separated string into a set of trimmed, non-empty values.

weed/worker/tasks/balance/detection_test.go

@@ -2,6 +2,7 @@ package balance
 
 import (
 	"fmt"
+	"strings"
 	"testing"
 
 	"github.com/seaweedfs/seaweedfs/weed/admin/topology"
@@ -1000,3 +1001,112 @@ func TestDetection_ZeroVolumeServerIncludedInBalance(t *testing.T) {
 	t.Logf("Distribution 8/2/1/0 → %v after %d moves (imbalance=%.1f%%)",
 		effective, len(tasks), imbalance*100)
 }
+
+func TestDetection_DataCenterFilter(t *testing.T) {
+	servers := []serverSpec{
+		{id: "node-a", diskType: "hdd", diskID: 1, dc: "dc1", rack: "rack1"},
+		{id: "node-b", diskType: "hdd", diskID: 2, dc: "dc1", rack: "rack1"},
+		{id: "node-c", diskType: "hdd", diskID: 3, dc: "dc2", rack: "rack1"},
+	}
+
+	var metrics []*types.VolumeHealthMetrics
+	metrics = append(metrics, makeVolumes("node-a", "hdd", "dc1", "rack1", "c1", 1, 50)...)
+	metrics = append(metrics, makeVolumes("node-b", "hdd", "dc1", "rack1", "c1", 100, 10)...)
+	// node-c is in dc2, should be excluded by filter
+	metrics = append(metrics, makeVolumes("node-c", "hdd", "dc2", "rack1", "c1", 200, 30)...)
+
+	// Only include metrics from dc1
+	dc1Metrics := make([]*types.VolumeHealthMetrics, 0)
+	for _, m := range metrics {
+		if m.DataCenter == "dc1" {
+			dc1Metrics = append(dc1Metrics, m)
+		}
+	}
+
+	at := buildTopology(servers, metrics)
+	clusterInfo := &types.ClusterInfo{ActiveTopology: at}
+
+	conf := defaultConf()
+	conf.DataCenterFilter = "dc1"
+
+	tasks, _, err := Detection(dc1Metrics, clusterInfo, conf, 100)
+	if err != nil {
+		t.Fatalf("Detection failed: %v", err)
+	}
+
+	// Ensure detection produced tasks so the following checks are not vacuous.
+	if len(tasks) == 0 {
+		t.Fatal("Expected balance tasks for 50/10 imbalance within dc1, got 0")
+	}
+
+	// With DC filter, only node-a and node-b are considered in topology seeding.
+	// node-c should never appear as source or destination.
+	for _, task := range tasks {
+		if task.Server == "node-c" {
+			t.Errorf("node-c (dc2) should not be a source with dc1 filter")
+		}
+		if task.TypedParams != nil {
+			for _, tgt := range task.TypedParams.Targets {
+				if strings.Contains(tgt.Node, "node-c") {
+					t.Errorf("node-c (dc2) should not be a target with dc1 filter")
+				}
+			}
+		}
+	}
+
+	if len(tasks) > 0 {
+		t.Logf("Created %d tasks within dc1 scope", len(tasks))
+	}
+}
+
+func TestDetection_NodeFilter(t *testing.T) {
+	servers := []serverSpec{
+		{id: "node-a", diskType: "hdd", diskID: 1, dc: "dc1", rack: "rack1"},
+		{id: "node-b", diskType: "hdd", diskID: 2, dc: "dc1", rack: "rack1"},
+		{id: "node-c", diskType: "hdd", diskID: 3, dc: "dc1", rack: "rack1"},
+	}
+
+	var metrics []*types.VolumeHealthMetrics
+	metrics = append(metrics, makeVolumes("node-a", "hdd", "dc1", "rack1", "c1", 1, 50)...)
+	metrics = append(metrics, makeVolumes("node-b", "hdd", "dc1", "rack1", "c1", 100, 10)...)
+	metrics = append(metrics, makeVolumes("node-c", "hdd", "dc1", "rack1", "c1", 200, 5)...)
+
+	// Only include metrics from node-a and node-b
+	filteredMetrics := make([]*types.VolumeHealthMetrics, 0)
+	for _, m := range metrics {
+		if m.Server == "node-a" || m.Server == "node-b" {
+			filteredMetrics = append(filteredMetrics, m)
+		}
+	}
+
+	at := buildTopology(servers, metrics)
+	clusterInfo := &types.ClusterInfo{ActiveTopology: at}
+
+	conf := defaultConf()
+	conf.NodeFilter = "node-a,node-b"
+
+	tasks, _, err := Detection(filteredMetrics, clusterInfo, conf, 100)
+	if err != nil {
+		t.Fatalf("Detection failed: %v", err)
+	}
+
+	// Ensure detection produced tasks so the following checks are not vacuous.
+	if len(tasks) == 0 {
+		t.Fatal("Expected balance tasks for 50/10 imbalance within node-a,node-b scope, got 0")
+	}
+
+	for _, task := range tasks {
+		if task.Server == "node-c" {
+			t.Errorf("node-c should not be a source with node filter")
+		}
+		if task.TypedParams != nil {
+			for _, tgt := range task.TypedParams.Targets {
+				if strings.Contains(tgt.Node, "node-c") {
+					t.Errorf("node-c should not be a target with node filter")
+				}
+			}
+		}
+	}
+
+	t.Logf("Created %d tasks within node-a,node-b scope", len(tasks))
+}

weed/worker/tasks/util/csv.go

@@ -0,0 +1,20 @@
+package util
+
+import "strings"
+
+// ParseCSVSet splits a comma-separated string into a set of trimmed,
+// non-empty values. Returns nil if the input is empty.
+func ParseCSVSet(csv string) map[string]bool {
+	csv = strings.TrimSpace(csv)
+	if csv == "" {
+		return nil
+	}
+	set := make(map[string]bool)
+	for _, item := range strings.Split(csv, ",") {
+		trimmed := strings.TrimSpace(item)
+		if trimmed != "" {
+			set[trimmed] = true
+		}
+	}
+	return set
+}