Chuong Tran created ZOOKEEPER-4921:
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Summary: Zookeeper Client 3.9.3 Fails to Reconnect After Network
Failures
Key: ZOOKEEPER-4921
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-4921
Project: ZooKeeper
Issue Type: Bug
Components: java client
Affects Versions: 3.9.3
Reporter: Chuong Tran
After upgrading the Java Zookeeper client to version 3.9.3, we observed that it
is not resilient to brief network disruptions, such as a short VPN blip. In
such cases, the client attempts to reconnect only once, and if unsuccessful,
the session expires.
{quote}Apr 23, 2025 10:19:23 AM
com.twitter.finagle.common.zookeeper.ZooKeeperClient$3 process
INFO: Zookeeper session expired. Event: WatchedEvent state:Expired type:None
path:null zxid: -1
{quote}
In contrast, the previous version (3.9.2) would continuously retry until the
network connection was restored, maintaining the session more reliably.
I believe it's a new issue with this change:
https://issues.apache.org/jira/browse/ZOOKEEPER-4508
Step to repro:
# Open VPN.
# Start the application which connects to the Zookeeper server with the VPN.
# Disable VPN for a couple of minutes.
# Observe the application.
# Enable the VPN again.
{quote}3.9.3:
"message" : "Session 0x0 for server XXX, Closing socket connection. Attempting
reconnect except it is a SessionExpiredException or SessionTimeoutException.",
"stackTrace" : "o.a.z.ClientCnxn$SessionTimeoutException: Client session
timed out, have not heard from server in 5590ms for session id 0x0
at o.a.z.ClientCnxn$SendThread.run(ClientCnxn.java:1253)
{quote}
3.9.2: Application will be connected successfully.
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