这是一个验证贴，因为社区文档是错误的。

先说结论

Flink1.15仅支持ZooKeeper3.5/3.6，不再支持3.4。FLINK-25146 Drop support for Zookeeper 3.4 

https://nightlies.apache.org/flink/flink-docs-release-1.16/release-notes/flink-1.15

社区文档

其中的ZooKeeper Versions描述默认使用3.4，可以自行调整为3.5。从文档上来看自1.11版本就添加了这段描述，到目前最新稳定版本(1.16.0)依然是这么描述的。但是实际我们在flink-1.15.0/lib目录中只看到了flink-shaded-zookeeper-3.5.9.jar，在opt目录中看到了flink-shaded-zookeeper-3.6.3.jar，即默认使用3.5版本，并在opt目录中放置了3.6版本。

其实在1.15的 ReleaseNote 中明确写了，不再支持3.4，只是还是有点不死心，做了如下的验证。

Release notes - Flink 1.15

Drop support for Zookeeper 3.4 #

FLINK-25146 # 

Support for using Zookeeper 3.4 for HA has been dropped. Users relying on Zookeeper need to upgrade to 3.5/3.6. By default Flink now uses a Zookeeper 3.5 client.

验证一

那么我们是否可以将3.4的版本（flink-1.13.3/lib/flink-shaded-zookeeper-3.4.14.jar）放置到flink-1.15.3/lib目录中，在1.15版本中使用3.4版本呢？

不能

如果我们这么做，将会遇到 java.lang.ClassNotFoundException: org.apache.flink.shaded.curator5.org.apache.curator.framework.api.ACLProvider ，完整堆栈如下：

 1 2022-12-08 18:18:05,693 INFO  org.apache.flink.runtime.rpc.akka.AkkaRpcService             [] - Stopping Akka RPC service.
 2 2022-12-08 18:18:05,734 INFO  akka.remote.RemoteActorRefProvider$RemotingTerminator        [] - Shutting down remote daemon.
 3 2022-12-08 18:18:05,736 INFO  akka.remote.RemoteActorRefProvider$RemotingTerminator        [] - Remote daemon shut down; proceeding with flushing remote transports.
 4 2022-12-08 18:18:05,758 INFO  akka.remote.RemoteActorRefProvider$RemotingTerminator        [] - Remoting shut down.
 5 2022-12-08 18:18:05,782 INFO  org.apache.flink.runtime.rpc.akka.AkkaRpcService             [] - Stopped Akka RPC service.
 6 2022-12-08 18:18:05,782 ERROR org.apache.flink.runtime.entrypoint.ClusterEntrypoint        [] - Could not start cluster entrypoint YarnApplicationClusterEntryPoint.
 7 org.apache.flink.runtime.entrypoint.ClusterEntrypointException: Failed to initialize the cluster entrypoint YarnApplicationClusterEntryPoint.
 8     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.startCluster(ClusterEntrypoint.java:250) ~[flink-dist-1.15.3.jar:1.15.3]
 9     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.runClusterEntrypoint(ClusterEntrypoint.java:711) [flink-dist-1.15.3.jar:1.15.3]
10     at org.apache.flink.yarn.entrypoint.YarnApplicationClusterEntryPoint.main(YarnApplicationClusterEntryPoint.java:112) [flink-dist-1.15.3.jar:1.15.3]
11 Caused by: java.lang.NoClassDefFoundError: org/apache/flink/shaded/curator5/org/apache/curator/framework/api/ACLProvider
12     at org.apache.flink.runtime.highavailability.HighAvailabilityServicesUtils.createZooKeeperHaServices(HighAvailabilityServicesUtils.java:90) ~[flink-dist-1.15.3.jar:1.15.3]
13     at org.apache.flink.runtime.highavailability.HighAvailabilityServicesUtils.createHighAvailabilityServices(HighAvailabilityServicesUtils.java:140) ~[flink-dist-1.15.3.jar:1.15.3]
14     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.createHaServices(ClusterEntrypoint.java:427) ~[flink-dist-1.15.3.jar:1.15.3]
15     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.initializeServices(ClusterEntrypoint.java:376) ~[flink-dist-1.15.3.jar:1.15.3]
16     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.runCluster(ClusterEntrypoint.java:277) ~[flink-dist-1.15.3.jar:1.15.3]
17     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.lambda$startCluster$1(ClusterEntrypoint.java:227) ~[flink-dist-1.15.3.jar:1.15.3]
18     at java.security.AccessController.doPrivileged(Native Method) ~[?:1.8.0_202]
19     at javax.security.auth.Subject.doAs(Subject.java:422) ~[?:1.8.0_202]
20     at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1875) ~[hadoop-common-3.0.0-cdh6.3.2.jar:?]
21     at org.apache.flink.runtime.security.contexts.HadoopSecurityContext.runSecured(HadoopSecurityContext.java:41) ~[flink-dist-1.15.3.jar:1.15.3]
22     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.startCluster(ClusterEntrypoint.java:224) ~[flink-dist-1.15.3.jar:1.15.3]
23     ... 2 more
24 Caused by: java.lang.ClassNotFoundException: org.apache.flink.shaded.curator5.org.apache.curator.framework.api.ACLProvider
25     at java.net.URLClassLoader.findClass(URLClassLoader.java:382) ~[?:1.8.0_202]
26     at java.lang.ClassLoader.loadClass(ClassLoader.java:424) ~[?:1.8.0_202]
27     at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349) ~[?:1.8.0_202]
28     at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[?:1.8.0_202]
29     at org.apache.flink.runtime.highavailability.HighAvailabilityServicesUtils.createZooKeeperHaServices(HighAvailabilityServicesUtils.java:90) ~[flink-dist-1.15.3.jar:1.15.3]
30     at org.apache.flink.runtime.highavailability.HighAvailabilityServicesUtils.createHighAvailabilityServices(HighAvailabilityServicesUtils.java:140) ~[flink-dist-1.15.3.jar:1.15.3]
31     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.createHaServices(ClusterEntrypoint.java:427) ~[flink-dist-1.15.3.jar:1.15.3]
32     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.initializeServices(ClusterEntrypoint.java:376) ~[flink-dist-1.15.3.jar:1.15.3]
33     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.runCluster(ClusterEntrypoint.java:277) ~[flink-dist-1.15.3.jar:1.15.3]
34     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.lambda$startCluster$1(ClusterEntrypoint.java:227) ~[flink-dist-1.15.3.jar:1.15.3]
35     at java.security.AccessController.doPrivileged(Native Method) ~[?:1.8.0_202]
36     at javax.security.auth.Subject.doAs(Subject.java:422) ~[?:1.8.0_202]
37     at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1875) ~[hadoop-common-3.0.0-cdh6.3.2.jar:?]
38     at org.apache.flink.runtime.security.contexts.HadoopSecurityContext.runSecured(HadoopSecurityContext.java:41) ~[flink-dist-1.15.3.jar:1.15.3]
39     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.startCluster(ClusterEntrypoint.java:224) ~[flink-dist-1.15.3.jar:1.15.3]
40     ... 2 more

验证二

如果使用3.5的客户端访问3.4版本服务端，将会提示 org.apache.flink.shaded.zookeeper3.org.apache.zookeeper.KeeperException$UnimplementedException: KeeperErrorCode = Unimplemented for 异常，完整堆栈如下：

 1 2022-12-08 15:10:14,935 ERROR org.apache.flink.runtime.entrypoint.ClusterEntrypoint        [] - Fatal error occurred in the cluster entrypoint.
 2 org.apache.flink.shaded.zookeeper3.org.apache.zookeeper.KeeperException$UnimplementedException: KeeperErrorCode = Unimplemented for /flink/jm_ha_metadata/application_1666841155139_0173
 3     at org.apache.flink.shaded.zookeeper3.org.apache.zookeeper.KeeperException.create(KeeperException.java:106) ~[flink-shaded-zookeeper-3-3.5.9-15.0.jar:3.5.9-15.0]
 4     at org.apache.flink.shaded.zookeeper3.org.apache.zookeeper.KeeperException.create(KeeperException.java:54) ~[flink-shaded-zookeeper-3-3.5.9-15.0.jar:3.5.9-15.0]
 5     at org.apache.flink.shaded.zookeeper3.org.apache.zookeeper.ZooKeeper.create(ZooKeeper.java:1538) ~[flink-shaded-zookeeper-3-3.5.9-15.0.jar:3.5.9-15.0]
 6     at org.apache.flink.shaded.curator5.org.apache.curator.utils.ZKPaths.mkdirs(ZKPaths.java:351) ~[flink-shaded-zookeeper-3-3.5.9-15.0.jar:3.5.9-15.0]
 7     at org.apache.flink.shaded.curator5.org.apache.curator.framework.imps.NamespaceImpl$1.call(NamespaceImpl.java:90) ~[flink-shaded-zookeeper-3-3.5.9-15.0.jar:3.5.9-15.0]
 8     at org.apache.flink.shaded.curator5.org.apache.curator.RetryLoop.callWithRetry(RetryLoop.java:93) ~[flink-shaded-zookeeper-3-3.5.9-15.0.jar:3.5.9-15.0]
 9     at org.apache.flink.shaded.curator5.org.apache.curator.framework.imps.NamespaceImpl.fixForNamespace(NamespaceImpl.java:83) ~[flink-shaded-zookeeper-3-3.5.9-15.0.jar:3.5.9-15.0]
10     at org.apache.flink.shaded.curator5.org.apache.curator.framework.imps.NamespaceImpl.newNamespaceAwareEnsurePath(NamespaceImpl.java:109) ~[flink-shaded-zookeeper-3-3.5.9-15.0.jar:3.5.9-15.0]
11     at org.apache.flink.shaded.curator5.org.apache.curator.framework.imps.CuratorFrameworkImpl.newNamespaceAwareEnsurePath(CuratorFrameworkImpl.java:618) ~[flink-shaded-zookeeper-3-3.5.9-15.0.jar:3.5.9-15.0]
12     at org.apache.flink.runtime.util.ZooKeeperUtils.useNamespaceAndEnsurePath(ZooKeeperUtils.java:729) ~[flink-runtime-1.15.2.jar:1.15.2]
13     at org.apache.flink.runtime.highavailability.zookeeper.ZooKeeperMultipleComponentLeaderElectionHaServices.<init>(ZooKeeperMultipleComponentLeaderElectionHaServices.java:85) ~[flink-runtime-1.15.2.jar:1.15.2]
14     at org.apache.flink.runtime.highavailability.HighAvailabilityServicesUtils.createZooKeeperHaServices(HighAvailabilityServicesUtils.java:96) ~[flink-runtime-1.15.2.jar:1.15.2]
15     at org.apache.flink.runtime.highavailability.HighAvailabilityServicesUtils.createHighAvailabilityServices(HighAvailabilityServicesUtils.java:140) ~[flink-runtime-1.15.2.jar:1.15.2]
16     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.createHaServices(ClusterEntrypoint.java:427) ~[flink-runtime-1.15.2.jar:1.15.2]
17     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.initializeServices(ClusterEntrypoint.java:376) ~[flink-runtime-1.15.2.jar:1.15.2]
18     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.runCluster(ClusterEntrypoint.java:277) ~[flink-runtime-1.15.2.jar:1.15.2]
19     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.lambda$startCluster$1(ClusterEntrypoint.java:227) ~[flink-runtime-1.15.2.jar:1.15.2]
20     at java.security.AccessController.doPrivileged(Native Method) ~[?:1.8.0_202]
21     at javax.security.auth.Subject.doAs(Subject.java:422) [?:1.8.0_202]
22     at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1875) [hadoop-common-3.0.0-cdh6.3.2.jar:?]
23     at org.apache.flink.runtime.security.contexts.HadoopSecurityContext.runSecured(HadoopSecurityContext.java:41) [flink-runtime-1.15.2.jar:1.15.2]
24     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.startCluster(ClusterEntrypoint.java:224) [flink-runtime-1.15.2.jar:1.15.2]
25     at org.apache.flink.runtime.entrypoint.ClusterEntrypoint.runClusterEntrypoint(ClusterEntrypoint.java:711) [flink-runtime-1.15.2.jar:1.15.2]
26     at org.apache.flink.yarn.entrypoint.YarnApplicationClusterEntryPoint.main(YarnApplicationClusterEntryPoint.java:112) [flink-dist-1.15.3.jar:1.15.3]
27 2022-12-08 15:10:14,943 INFO  org.apache.flink.runtime.entrypoint.ClusterEntrypoint        [] - Shutting YarnApplicationClusterEntryPoint down with application status UNKNOWN. Diagnostics Cluster entrypoint has been closed externally..

参考资料：

1. FLINK-25146Drop support for Zookeeper 3.4

2. ZooKeeper Version 3.4.x Compatibility

3. https://nightlies.apache.org/flink/flink-docs-release-1.16/release-notes/flink-1.15/