Make ZkBookieRackAffinityMapping work as expected (apache#6917)

### Motivation

The current bookie rack affinity logic is problematic. The rack map is expecting a `host:port` pair but the bookkeeper DNS resolver is expecting a hostname or a host address. 

### Modification

- Introduce a new HashMap to keep a mapping between hostname and bookie info. It maintains the mapping for bookkeeper DNS resolver to lookup the network location.

pulsar-zookeeper-utils/src/main/java/org/apache/pulsar/zookeeper/ZkBookieRackAffinityMapping.java

@@ -20,8 +20,10 @@
 
 import com.fasterxml.jackson.databind.ObjectMapper;
 
+import java.net.InetAddress;
 import java.net.UnknownHostException;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
@@ -58,6 +60,7 @@ public class ZkBookieRackAffinityMapping extends AbstractDNSToSwitchMapping
     private static final ObjectMapper jsonMapper = ObjectMapperFactory.create();
 
     private volatile BookiesRackConfiguration racksWithHost = new BookiesRackConfiguration();
+    private volatile Map<String, BookieInfo> bookieInfoMap = new HashMap<>();
 
     @Override
     public void setConf(Configuration conf) {
@@ -77,17 +80,32 @@ private void updateRacksWithHost(BookiesRackConfiguration racks) {
         // for just the IP/hostname when trying to get the rack for a bookie.
         // To work around this issue, we insert in the map the bookie ip/hostname with same rack-info
         BookiesRackConfiguration newRacksWithHost = new BookiesRackConfiguration();
+        Map<String, BookieInfo> newBookieInfoMap = new HashMap<>();
         racks.forEach((group, bookies) ->
                 bookies.forEach((addr, bi) -> {
                     try {
                         BookieSocketAddress bsa = new BookieSocketAddress(addr);
-                        newRacksWithHost.updateBookie(group, bsa.getHostName(), bi);
+                        newRacksWithHost.updateBookie(group, bsa.toString(), bi);
+
+                        String hostname = bsa.getSocketAddress().getHostName();
+                        newBookieInfoMap.put(hostname, bi);
+
+                        InetAddress address = bsa.getSocketAddress().getAddress();
+                        if (null != address) {
+                            String hostIp = address.getHostAddress();
+                            if (null != hostIp) {
+                                newBookieInfoMap.put(hostIp, bi);
+                            }
+                        } else {
+                            LOG.info("Network address for {} is unresolvable yet.", addr);
+                        }
                     } catch (UnknownHostException e) {
                         throw new RuntimeException(e);
                     }
                 })
         );
         racksWithHost = newRacksWithHost;
+        bookieInfoMap = newBookieInfoMap;
     }
 
     private ZooKeeperDataCache<BookiesRackConfiguration> getAndSetZkCache(Configuration conf) {
@@ -162,10 +180,19 @@ private String getRack(String bookieAddress) {
             throw new RuntimeException(e);
         }
 
+        BookieInfo bi = bookieInfoMap.get(bookieAddress);
+        if (bi == null) {
+            Optional<BookieInfo> biOpt = racksWithHost.getBookie(bookieAddress);
+            if (biOpt.isPresent()) {
+                bi = biOpt.get();
+            } else {
+                updateRacksWithHost(racksWithHost);
+                bi = bookieInfoMap.get(bookieAddress);
+            }
+        }
 
-        Optional<BookieInfo> bi = racksWithHost.getBookie(bookieAddress);
-        if (bi.isPresent()) {
-            String rack = bi.get().getRack();
+        if (bi != null) {
+            String rack = bi.getRack();
             if (!rack.startsWith("/")) {
                 rack = "/" + rack;
             }