zhangmeng916 commented on a change in pull request #1043:
URL: https://github.com/apache/helix/pull/1043#discussion_r432998959



##########
File path: 
helix-core/src/main/java/org/apache/helix/controller/rebalancer/topology/Topology.java
##########
@@ -212,123 +186,106 @@ private static Node cloneTree(Node root, Map<Node, 
Integer> newNodeWeight, Set<N
     return newRoot;
   }
 
-  /**
-   * Creates a tree representing the cluster structure using default cluster 
topology definition
-   * (i,e no topology definition given and no domain id set).
-   */
-  private Node createClusterTreeWithDefaultTopologyDef() {
+  private Node createClusterTree() {
     // root
     Node root = new Node();
     root.setName("root");
     root.setId(computeId("root"));
     root.setType(Types.ROOT.name());
 
-    for (String ins : _allInstances) {
-      InstanceConfig config = _instanceConfigMap.get(ins);
-      Map<String, String> pathValueMap = new HashMap<>();
-      if (_topologyAwareEnabled) {
-        String zone = config.getZoneId();
+    for (String instance : _allInstances) {
+      InstanceConfig insConfig = _instanceConfigMap.get(instance);
+      LinkedHashMap<String, String> instanceTopologyMap = new 
LinkedHashMap<>();
+      if (computeInstanceTopologyMap(_clusterConfig, instance, insConfig, 
instanceTopologyMap)) {
+        int weight = insConfig.getWeight();
+        if (weight < 0 || weight == InstanceConfig.WEIGHT_NOT_SET) {
+          weight = DEFAULT_NODE_WEIGHT;
+        }
+        addEndNode(root, instance, instanceTopologyMap, weight, 
_liveInstances);
+      }
+    }
+    return root;
+  }
+
+  private boolean computeInstanceTopologyMap(ClusterConfig clusterConfig, 
String instance,
+      InstanceConfig instanceConfig, LinkedHashMap<String, String> 
instanceTopologyMap) {
+    if (clusterConfig.isTopologyAwareEnabled()) {
+      String topologyDef = clusterConfig.getTopology();
+      if (topologyDef == null) {
+        // Return a map using default cluster topology definition, i,e. 
/root/zone/instance
+        String zone = instanceConfig.getZoneId();
         if (zone == null) {
           // we have the hierarchy style of domain id for instance.
-          if (config.getInstanceEnabled() && 
(_clusterConfig.getDisabledInstances() == null
-              || !_clusterConfig.getDisabledInstances().containsKey(ins))) {
+          if (instanceConfig.getInstanceEnabled() && 
(clusterConfig.getDisabledInstances() == null
+              || !clusterConfig.getDisabledInstances().containsKey(instance))) 
{
             // if enabled instance missing ZONE_ID information, fails the 
rebalance.
             throw new HelixException(String
-                .format("ZONE_ID for instance %s is not set, failed the 
topology-aware placement!",
-                    ins));
+                .format("ZONE_ID for instance %s is not set, fail the 
topology-aware placement!",
+                    instance));
           } else {
             // if the disabled instance missing ZONE setting, ignore it should 
be fine.
-            logger.warn(String
-                .format("ZONE_ID for instance %s is not set, failed the 
topology-aware placement!",
-                    ins));
-            continue;
+            logger.warn("ZONE_ID for instance {} is not set, ignore the 
instance!", instance);
+            return false;
           }
-
         }
-        pathValueMap.put(Types.ZONE.name(), zone);
-      }
-      pathValueMap.put(Types.INSTANCE.name(), ins);
-      int weight = config.getWeight();
-      if (weight < 0 || weight == InstanceConfig.WEIGHT_NOT_SET) {
-        weight = DEFAULT_NODE_WEIGHT;
-      }
-      root = addEndNode(root, ins, pathValueMap, weight, _liveInstances);
-    }
-    return root;
-  }
-
-  /**
-   * Creates a tree representing the cluster structure using default cluster 
topology definition
-   * (i,e no topology definition given and no domain id set).
-   */
-  private Node createClusterTreeWithCustomizedTopology() {
-    // root
-    Node root = new Node();
-    root.setName("root");
-    root.setId(computeId("root"));
-    root.setType(Types.ROOT.name());
-
-    for (String ins : _allInstances) {
-      InstanceConfig insConfig = _instanceConfigMap.get(ins);
-      String domain = insConfig.getDomainAsString();
-      if (domain == null) {
-        if (insConfig.getInstanceEnabled() && 
(_clusterConfig.getDisabledInstances() == null
-            || !_clusterConfig.getDisabledInstances().containsKey(ins))) {
-          // if enabled instance missing domain information, fails the 
rebalance.
-          throw new HelixException(String
-              .format("Domain for instance %s is not set, failed the 
topology-aware placement!",
-                  ins));
-        } else {
-          // if the disabled instance missing domain setting, ignore it should 
be fine.
-          logger
-              .warn(String.format("Domain for instance %s is not set, ignore 
the instance!", ins));
-          continue;
+        instanceTopologyMap.put(Types.ZONE.name(), zone);
+        instanceTopologyMap.put(Types.INSTANCE.name(), instance);
+      } else {
+        /*
+         * Return a map representing the cluster structure using cluster 
topology defined in
+         * TOPOLOGY in ClusterConfig.
+         */
+        String domain = instanceConfig.getDomainAsString();
+        if (domain == null || domain.isEmpty()) {
+          if (instanceConfig.getInstanceEnabled() && 
(clusterConfig.getDisabledInstances() == null
+              || !clusterConfig.getDisabledInstances().containsKey(instance))) 
{
+            // if enabled instance missing domain information, fails the 
rebalance.
+            throw new HelixException(String
+                .format("Domain for instance %s is not set, fail the 
topology-aware placement!",
+                    instance));
+          } else {
+            // if the disabled instance missing domain setting, ignore it 
should be fine.
+            logger.warn("Domain for instance {} is not set, ignore the 
instance!", instance);
+            return false;
+          }
         }
-      }
-
-      String[] pathPairs = domain.trim().split(",");
-      Map<String, String> pathValueMap = new HashMap<>();
-      for (String pair : pathPairs) {
-        String[] values = pair.trim().split("=");
-        if (values.length != 2 || values[0].isEmpty() || values[1].isEmpty()) {
+        Map<String, String> domainAsMap;
+        try {
+          domainAsMap = instanceConfig.getDomainAsMap();
+        } catch (IllegalArgumentException e) {
           throw new HelixException(String.format(
-              "Domain-Value pair %s for instance %s is not valid, failed the 
topology-aware placement!",
-              pair, ins));
+              "Domain %s for instance %s is not valid, fail the topology-aware 
placement!",
+              domain, instance));
         }
-        String type = values[0];
-        String value = values[1];
-
-        if (!_types.contains(type)) {
-          logger.warn(String
-              .format("Path %s defined in domain of instance %s not 
recognized, ignored!", pair,
-                  ins));
-          continue;
+        String[] topologyKeys = topologyDef.trim().split("/");
+        for (String key : topologyKeys) {
+          if (!key.isEmpty()) {
+            // if a key does not exist in the instance domain config, apply 
the default domain value.
+            String value = domainAsMap.get(key);
+            if (value == null || value.length()==0) {
+              value = _defaultPathPrefix + key;
+            }
+            instanceTopologyMap.put(key, value);

Review comment:
       I'd like to know the rationale of setting default value. Basically if 
the "domain" field is not set, we throw an exception, but if the "domain" is 
set with a random value, we think it is fine and give it a default zone value. 
How do we know it doesn't cause problem for rebalance.




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