diff --git a/internal/datacoord/cluster.go b/internal/datacoord/cluster.go
index 3c8af986f4..cdc20d2baa 100644
--- a/internal/datacoord/cluster.go
+++ b/internal/datacoord/cluster.go
@@ -71,7 +71,7 @@ func defaultRegisterPolicy() dataNodeRegisterPolicy {
 }
 
 func defaultUnregisterPolicy() dataNodeUnregisterPolicy {
-	return &randomAssignUnregisterPolicy{}
+	return randomAssignRegisterFunc
 }
 
 func defaultAssignPolicy() channelAssignPolicy {
diff --git a/internal/datacoord/policy.go b/internal/datacoord/policy.go
index b27451e0f4..0a2571eaeb 100644
--- a/internal/datacoord/policy.go
+++ b/internal/datacoord/policy.go
@@ -8,6 +8,7 @@
 // Unless required by applicable law or agreed to in writing, software distributed under the License
 // is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 // or implied. See the License for the specific language governing permissions and limitations under the License.
+
 package datacoord
 
 import (
@@ -25,6 +26,8 @@ type clusterDeltaChange struct {
 	offlines []string
 	restarts []string
 }
+
+// clusterStartupPolicy defines the behavior when datacoord starts/restarts
 type clusterStartupPolicy interface {
 	// apply accept all nodes and new/offline/restarts nodes and returns datanodes whose status need to be changed
 	apply(oldCluster map[string]*datapb.DataNodeInfo, delta *clusterDeltaChange, buffer []*datapb.ChannelStatus) ([]*datapb.DataNodeInfo, []*datapb.ChannelStatus)
@@ -34,10 +37,20 @@ type watchRestartsStartupPolicy struct {
 }
 
 func newWatchRestartsStartupPolicy() clusterStartupPolicy {
-	return &watchRestartsStartupPolicy{}
+	return watchRestartStartup
 }
 
-func (p *watchRestartsStartupPolicy) apply(cluster map[string]*datapb.DataNodeInfo, delta *clusterDeltaChange,
+// startup func
+type startupFunc func(cluster map[string]*datapb.DataNodeInfo, delta *clusterDeltaChange,
+	buffer []*datapb.ChannelStatus) ([]*datapb.DataNodeInfo, []*datapb.ChannelStatus)
+
+// implement watchRestartsStartupPolicy for startupFunc
+func (f startupFunc) apply(cluster map[string]*datapb.DataNodeInfo, delta *clusterDeltaChange,
+	buffer []*datapb.ChannelStatus) ([]*datapb.DataNodeInfo, []*datapb.ChannelStatus) {
+	return f(cluster, delta, buffer)
+}
+
+var watchRestartStartup startupFunc = func(cluster map[string]*datapb.DataNodeInfo, delta *clusterDeltaChange,
 	buffer []*datapb.ChannelStatus) ([]*datapb.DataNodeInfo, []*datapb.ChannelStatus) {
 	ret := make([]*datapb.DataNodeInfo, 0)
 	for _, addr := range delta.restarts {
@@ -90,54 +103,64 @@ func (p *watchRestartsStartupPolicy) apply(cluster map[string]*datapb.DataNodeIn
 	return ret, buffer
 }
 
+// dataNodeRegisterPolicy defines the behavior when a datanode is registered
 type dataNodeRegisterPolicy interface {
 	// apply accept all online nodes and new created node, returns nodes needed to be changed
 	apply(cluster map[string]*datapb.DataNodeInfo, session *datapb.DataNodeInfo, buffer []*datapb.ChannelStatus) ([]*datapb.DataNodeInfo, []*datapb.ChannelStatus)
 }
 
-type emptyRegisterPolicy struct {
+// data node register func, simple func wrapping policy
+type dataNodeRegisterFunc func(cluster map[string]*datapb.DataNodeInfo, session *datapb.DataNodeInfo, buffer []*datapb.ChannelStatus) ([]*datapb.DataNodeInfo, []*datapb.ChannelStatus)
+
+// implement dataNodeRegisterPolicy for dataNodeRegisterFunc
+func (f dataNodeRegisterFunc) apply(cluster map[string]*datapb.DataNodeInfo, session *datapb.DataNodeInfo,
+	buffer []*datapb.ChannelStatus) ([]*datapb.DataNodeInfo, []*datapb.ChannelStatus) {
+	return f(cluster, session, buffer)
 }
 
-func newEmptyRegisterPolicy() dataNodeRegisterPolicy {
-	return &emptyRegisterPolicy{}
-}
-
-func (p *emptyRegisterPolicy) apply(cluster map[string]*datapb.DataNodeInfo, session *datapb.DataNodeInfo,
+// test logic, register and do nothing
+var emptyRegister dataNodeRegisterFunc = func(cluster map[string]*datapb.DataNodeInfo, session *datapb.DataNodeInfo,
 	buffer []*datapb.ChannelStatus) ([]*datapb.DataNodeInfo, []*datapb.ChannelStatus) {
 	return []*datapb.DataNodeInfo{session}, buffer
 }
 
-type assignBufferRegisterPolicy struct{}
-
-func newAssiggBufferRegisterPolicy() dataNodeRegisterPolicy {
-	return &assignBufferRegisterPolicy{}
-}
-
-func (p *assignBufferRegisterPolicy) apply(cluster map[string]*datapb.DataNodeInfo, session *datapb.DataNodeInfo,
+// assign existing buffered channels into newly registered data node session
+var registerAssignWithBuffer dataNodeRegisterFunc = func(cluster map[string]*datapb.DataNodeInfo, session *datapb.DataNodeInfo,
 	buffer []*datapb.ChannelStatus) ([]*datapb.DataNodeInfo, []*datapb.ChannelStatus) {
 	session.Channels = append(session.Channels, buffer...)
 	return []*datapb.DataNodeInfo{session}, []*datapb.ChannelStatus{}
 }
 
+func newEmptyRegisterPolicy() dataNodeRegisterPolicy {
+	return emptyRegister
+}
+
+func newAssiggBufferRegisterPolicy() dataNodeRegisterPolicy {
+	return registerAssignWithBuffer
+}
+
+// dataNodeUnregisterPolicy defines the behavior when datanode unregisters
 type dataNodeUnregisterPolicy interface {
 	// apply accept all online nodes and unregistered node, returns nodes needed to be changed
 	apply(cluster map[string]*datapb.DataNodeInfo, session *datapb.DataNodeInfo) []*datapb.DataNodeInfo
 }
 
-type emptyUnregisterPolicy struct {
+// unregisterNodeFunc, short cut for functions implement policy
+type unregisterNodeFunc func(cluster map[string]*datapb.DataNodeInfo, session *datapb.DataNodeInfo) []*datapb.DataNodeInfo
+
+// implement dataNodeUnregisterPolicy for unregisterNodeFunc
+func (f unregisterNodeFunc) apply(cluster map[string]*datapb.DataNodeInfo, session *datapb.DataNodeInfo) []*datapb.DataNodeInfo {
+	return f(cluster, session)
 }
 
-func newEmptyUnregisterPolicy() dataNodeUnregisterPolicy {
-	return &emptyUnregisterPolicy{}
-}
-
-func (p *emptyUnregisterPolicy) apply(cluster map[string]*datapb.DataNodeInfo, session *datapb.DataNodeInfo) []*datapb.DataNodeInfo {
+// test logic, do nothing when node unregister
+var emptyUnregisterFunc unregisterNodeFunc = func(cluster map[string]*datapb.DataNodeInfo, session *datapb.DataNodeInfo) []*datapb.DataNodeInfo {
 	return nil
 }
 
-type randomAssignUnregisterPolicy struct{}
-
-func (p *randomAssignUnregisterPolicy) apply(cluster map[string]*datapb.DataNodeInfo, session *datapb.DataNodeInfo) []*datapb.DataNodeInfo {
+// randomly assign channels from unregistered node into existing nodes
+// if there is no nodes online, this func will not be invoked, buffer will be filled outside this func
+var randomAssignRegisterFunc unregisterNodeFunc = func(cluster map[string]*datapb.DataNodeInfo, session *datapb.DataNodeInfo) []*datapb.DataNodeInfo {
 	if len(cluster) == 0 || // no available node
 		session == nil ||
 		len(session.Channels) == 0 { // lost node not watching any channels
@@ -178,19 +201,27 @@ func (p *randomAssignUnregisterPolicy) apply(cluster map[string]*datapb.DataNode
 	return appliedNodes
 }
 
+func newEmptyUnregisterPolicy() dataNodeUnregisterPolicy {
+	return emptyUnregisterFunc
+}
+
+// channelAssignPolicy defines the behavior when a new channel needs to be assigned
 type channelAssignPolicy interface {
 	// apply accept all online nodes and new created channel with collectionID, returns node needed to be changed
 	apply(cluster map[string]*datapb.DataNodeInfo, channel string, collectionID UniqueID) []*datapb.DataNodeInfo
 }
 
-type assignAllPolicy struct {
+// channelAssignFunc, function shortcut for policy
+type channelAssignFunc func(cluster map[string]*datapb.DataNodeInfo, channel string, collectionID UniqueID) []*datapb.DataNodeInfo
+
+// implement channelAssignPolicy for channelAssign func
+func (f channelAssignFunc) apply(cluster map[string]*datapb.DataNodeInfo, channel string, collectionID UniqueID) []*datapb.DataNodeInfo {
+	return f(cluster, channel, collectionID)
 }
 
-func newAssignAllPolicy() channelAssignPolicy {
-	return &assignAllPolicy{}
-}
-
-func (p *assignAllPolicy) apply(cluster map[string]*datapb.DataNodeInfo, channel string, collectionID UniqueID) []*datapb.DataNodeInfo {
+// deprecated
+// test logic, assign channel to all existing data node, works fine only when there is only one data node!
+var assignAllFunc channelAssignFunc = func(cluster map[string]*datapb.DataNodeInfo, channel string, collectionID UniqueID) []*datapb.DataNodeInfo {
 	ret := make([]*datapb.DataNodeInfo, 0)
 	for _, node := range cluster {
 		has := false
@@ -214,13 +245,8 @@ func (p *assignAllPolicy) apply(cluster map[string]*datapb.DataNodeInfo, channel
 	return ret
 }
 
-type balancedAssignPolicy struct{}
-
-func newBalancedAssignPolicy() channelAssignPolicy {
-	return &balancedAssignPolicy{}
-}
-
-func (p *balancedAssignPolicy) apply(cluster map[string]*datapb.DataNodeInfo, channel string, collectionID UniqueID) []*datapb.DataNodeInfo {
+// balanced assign channel, select the datanode with least amount of channels to assign
+var balancedAssignFunc channelAssignFunc = func(cluster map[string]*datapb.DataNodeInfo, channel string, collectionID UniqueID) []*datapb.DataNodeInfo {
 	if len(cluster) == 0 {
 		return []*datapb.DataNodeInfo{}
 	}
@@ -249,3 +275,11 @@ func (p *balancedAssignPolicy) apply(cluster map[string]*datapb.DataNodeInfo, ch
 	ret = append(ret, cluster[target])
 	return ret
 }
+
+func newAssignAllPolicy() channelAssignPolicy {
+	return assignAllFunc
+}
+
+func newBalancedAssignPolicy() channelAssignPolicy {
+	return balancedAssignFunc
+}
diff --git a/internal/datacoord/policy_test.go b/internal/datacoord/policy_test.go
index fa0ad6c35a..546bccdf1d 100644
--- a/internal/datacoord/policy_test.go
+++ b/internal/datacoord/policy_test.go
@@ -57,7 +57,7 @@ func TestWatchRestartsPolicy(t *testing.T) {
 }
 
 func TestRandomReassign(t *testing.T) {
-	p := randomAssignUnregisterPolicy{}
+	p := randomAssignRegisterFunc
 
 	clusters := make(map[string]*datapb.DataNodeInfo)
 	clusters["addr1"] = &datapb.DataNodeInfo{