Fix cluster process update on metadata change

cluster/leader.go

@@ -1,7 +1,9 @@
 package cluster
 
 import (
+	"bytes"
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"sort"
@@ -571,7 +573,7 @@ func (c *cluster) doSynchronize(emergency bool) {
 
 	opStack, _, reality := synchronize(wish, want, have, nodesMap, c.nodeRecoverTimeout)
 
-	if !emergency {
+	if !emergency && len(opStack) != 0 {
 		cmd := &store.Command{
 			Operation: store.OpSetProcessNodeMap,
 			Data: store.CommandSetProcessNodeMap{
@@ -606,6 +608,55 @@ func (c *cluster) doRebalance(emergency bool) {
 	c.applyOpStack(opStack)
 }
 
+// isMetadataUpdateRequired compares two metadata. It relies on the documents property that json.Marshal
+// sorts the map keys prior encoding.
+func isMetadataUpdateRequired(wantMap map[string]interface{}, haveMap map[string]interface{}) (bool, map[string]interface{}) {
+	hasChanges := false
+	changeMap := map[string]interface{}{}
+
+	haveMapKeys := map[string]struct{}{}
+
+	for key := range haveMap {
+		haveMapKeys[key] = struct{}{}
+	}
+
+	for key, wantMapValue := range wantMap {
+		haveMapValue, ok := haveMap[key]
+		if !ok {
+			// A key in map1 exists, that doesn't exist in map2, we need to update
+			hasChanges = true
+		}
+
+		// Compare the values
+		changesData, err := json.Marshal(wantMapValue)
+		if err != nil {
+			continue
+		}
+
+		completeData, err := json.Marshal(haveMapValue)
+		if err != nil {
+			continue
+		}
+
+		if !bytes.Equal(changesData, completeData) {
+			// The values are not equal, we need to update
+			hasChanges = true
+		}
+
+		delete(haveMapKeys, key)
+
+		changeMap[key] = wantMapValue
+	}
+
+	for key := range haveMapKeys {
+		// If there keys in map2 that are not in map1, we have to update
+		hasChanges = true
+		changeMap[key] = nil
+	}
+
+	return hasChanges, changeMap
+}
+
 // synchronize returns a list of operations in order to adjust the "have" list to the "want" list
 // with taking the available resources on each node into account.
 func synchronize(wish map[string]string, want []store.Process, have []proxy.Process, nodes map[string]proxy.NodeAbout, nodeRecoverTimeout time.Duration) ([]interface{}, map[string]proxy.NodeResources, map[string]string) {
@@ -654,13 +705,15 @@ func synchronize(wish map[string]string, want []store.Process, have []proxy.Proc
 
 			continue
 		} else {
-			// The process is on the wantMap. Update the process if the configuration differ.
-			if !wantP.Config.Equal(haveP.Config) {
+			// The process is on the wantMap. Update the process if the configuration and/or metadata differ.
+			hasConfigChanges := !wantP.Config.Equal(haveP.Config)
+			hasMetadataChanges, metadata := isMetadataUpdateRequired(wantP.Metadata, haveP.Metadata)
+			if hasConfigChanges || hasMetadataChanges {
 				opStack = append(opStack, processOpUpdate{
 					nodeid:    haveP.NodeID,
 					processid: haveP.Config.ProcessID(),
 					config:    wantP.Config,
-					metadata:  wantP.Metadata,
+					metadata:  metadata,
 				})
 			}
 		}