[#772] fix(kerberos): cache proxy user ugi to avoid memory leak (#773)

1. To avoid memory leak by caching of proxy user UGI.

Fix: #772

The Hadoop filesystem instance will be created too many time in cache,
which will cause the shuffle server memory leak.

As we know, the filesystem cache's key is built by the scheme、authority and UGI.
The scheme and authority are not changed every time. But for UGI, if we invoke the
createProxyUser, it will always create a new one, that means the every invoking `Filesystem.get()`,
it will be cached due to different key.

No.

1. Existing UTs
2. Added tests

common/src/main/java/org/apache/uniffle/common/security/HadoopSecurityContext.java

@@ -19,11 +19,14 @@
 
 import java.io.IOException;
 import java.security.PrivilegedExceptionAction;
+import java.util.Map;
 import java.util.concurrent.Callable;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
 
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.collect.Maps;
 import org.apache.commons.lang3.StringUtils;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.security.UserGroupInformation;
@@ -39,6 +42,12 @@ public class HadoopSecurityContext implements SecurityContext {
   private UserGroupInformation loginUgi;
   private ScheduledExecutorService refreshScheduledExecutor;
 
+  // The purpose of the proxy user ugi cache is to prevent the creation of
+  // multiple cache keys for the same user, scheme, and authority in the Hadoop filesystem.
+  // Without this cache, large amounts of unnecessary filesystem instances could be stored in memory,
+  // leading to potential memory leaks. For more information on this issue, refer to #706.
+  private Map<String, UserGroupInformation> proxyUserUgiPool;
+
   public HadoopSecurityContext(
       String krb5ConfPath,
       String keytabFile,
@@ -76,6 +85,7 @@ public HadoopSecurityContext(
         refreshIntervalSec,
         refreshIntervalSec,
         TimeUnit.SECONDS);
+    proxyUserUgiPool = Maps.newConcurrentMap();
   }
 
   private void authRefresh() {
@@ -95,8 +105,10 @@ public <T> T runSecured(String user, Callable<T> securedCallable) throws Excepti
 
     // Run with the proxy user.
     if (!user.equals(loginUgi.getShortUserName())) {
+      UserGroupInformation proxyUserUgi =
+          proxyUserUgiPool.computeIfAbsent(user, x -> UserGroupInformation.createProxyUser(x, loginUgi));
       return executeWithUgiWrapper(
-          UserGroupInformation.createProxyUser(user, loginUgi),
+          proxyUserUgi,
           securedCallable
       );
     }
@@ -114,10 +126,20 @@ private <T> T executeWithUgiWrapper(UserGroupInformation ugi, Callable<T> callab
     return ugi.doAs((PrivilegedExceptionAction<T>) callable::call);
   }
 
+  // Only for tests
+  @VisibleForTesting
+  Map<String, UserGroupInformation> getProxyUserUgiPool() {
+    return proxyUserUgiPool;
+  }
+
   @Override
   public void close() throws IOException {
     if (refreshScheduledExecutor != null) {
       refreshScheduledExecutor.shutdown();
     }
+    if (proxyUserUgiPool != null) {
+      proxyUserUgiPool.clear();
+      proxyUserUgiPool = null;
+    }
   }
 }

common/src/test/java/org/apache/uniffle/common/security/HadoopSecurityContextTest.java

@@ -18,10 +18,13 @@
 package org.apache.uniffle.common.security;
 
 import java.util.concurrent.Callable;
+import java.util.concurrent.atomic.AtomicReference;
 
 import org.apache.commons.lang3.StringUtils;
 import org.apache.hadoop.fs.FileStatus;
+import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.security.UserGroupInformation;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
 
@@ -66,13 +69,28 @@ public void testSecuredCallable() throws Exception {
 
       // case3: run by the proxy user
       Path pathWithAlexUser = new Path("/alex/HadoopSecurityContextTest");
+      AtomicReference<UserGroupInformation> ugi1 = new AtomicReference<>();
       context.runSecured("alex", (Callable<Void>) () -> {
+        ugi1.set(UserGroupInformation.getCurrentUser());
         kerberizedHdfs.getFileSystem().mkdirs(pathWithAlexUser);
         return null;
       });
       fileStatus = kerberizedHdfs.getFileSystem().getFileStatus(pathWithAlexUser);
       assertEquals("alex", fileStatus.getOwner());
 
+      // case4: run by the proxy user again, it will always return the same
+      // ugi and filesystem instance.
+      AtomicReference<UserGroupInformation> ugi2 = new AtomicReference<>();
+      context.runSecured("alex", (Callable<Void>) () -> {
+        ugi2.set(UserGroupInformation.getCurrentUser());
+        return null;
+      });
+      assertTrue(ugi1.get() == ugi2.get());
+      assertTrue(ugi1.get() == context.getProxyUserUgiPool().get("alex"));
+
+      FileSystem fileSystem1 = context.runSecured("alex", () -> FileSystem.get(kerberizedHdfs.getConf()));
+      FileSystem fileSystem2 = context.runSecured("alex", () -> FileSystem.get(kerberizedHdfs.getConf()));
+      assertTrue(fileSystem1 == fileSystem2);
     }
   }