Igor Skokov created ZOOKEEPER-3320:
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Summary: Don't give up on bind of leader election port
Key: ZOOKEEPER-3320
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3320
Project: ZooKeeper
Issue Type: Bug
Components: leaderElection
Affects Versions: 3.5.4, 3.4.10
Reporter: Igor Skokov
When trying to run Zookeeper 3.5.4 cluster on Kubernetes, I found out that in
some circumstances Zookeeper node stop listening on leader election port. This
cause unavailability of ZK cluster.
Zookeeper deployed as StatefulSet in term of Kubernetes and has following
dynamic configuration:
{code:java}
zookeeper-0.zookeeper:2182:2183:participant;2181
zookeeper-1.zookeeper:2182:2183:participant;2181
zookeeper-2.zookeeper:2182:2183:participant;2181
{code}
Bind address contains DNS name which generated by Kubernetes for each
StatefulSet pod.
These DNS names will become resolvable after container start, but with some
delay. That delay cause stopping of leader election port listener in
QuorumCnxManager.Listener class.
Error happens in QuorumCnxManager.Listener "run" method, it tries to bind
leader election port to hostname which not resolvable at this moment. Retry
count is hard-coded and equals to 3(with backoff of 1 sec).
Zookeeper server log contains following errors:
{code:java}
2019-03-17 07:56:04,844 [myid:1] - WARN
[QuorumPeer[myid=1](plain=/0.0.0.0:2181)(secure=disabled):QuorumPeer@1230] -
Unexpected exception
java.net.SocketException: Unresolved address
at java.base/java.net.ServerSocket.bind(ServerSocket.java:374)
at java.base/java.net.ServerSocket.bind(ServerSocket.java:335)
at org.apache.zookeeper.server.quorum.Leader.<init>(Leader.java:241)
at
org.apache.zookeeper.server.quorum.QuorumPeer.makeLeader(QuorumPeer.java:1023)
at
org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:1226)
2019-03-17 07:56:04,844 [myid:1] - WARN
[QuorumPeer[myid=1](plain=/0.0.0.0:2181)(secure=disabled):QuorumPeer@1261] -
PeerState set to LOOKING
2019-03-17 07:56:04,845 [myid:1] - INFO
[QuorumPeer[myid=1](plain=/0.0.0.0:2181)(secure=disabled):QuorumPeer@1136] -
LOOKING
2019-03-17 07:56:04,845 [myid:1] - INFO
[QuorumPeer[myid=1](plain=/0.0.0.0:2181)(secure=disabled):FastLeaderElection@893]
- New election. My id = 1, proposed zxid=0x0
2019-03-17 07:56:04,846 [myid:1] - INFO
[WorkerReceiver[myid=1]:FastLeaderElection@687] - Notification: 2 (message
format version), 1 (n.leader), 0x0 (n.zxid), 0xf (n.round), LOOKING (n.state),
1 (n.sid), 0x0 (n.peerEPoch), LOOKING (my state)0 (n.config version)
2019-03-17 07:56:04,979 [myid:1] - INFO
[zookeeper-0.zookeeper:2183:QuorumCnxManager$Listener@892] - Leaving listener
2019-03-17 07:56:04,979 [myid:1] - ERROR
[zookeeper-0.zookeeper:2183:QuorumCnxManager$Listener@894] - As I'm leaving the
listener thread, I won't be able to participate in leader election any longer:
zookeeper-0.zookeeper:2183
{code}
This error happens on most nodes on cluster start and Zookeeper is unable to
form quorum. This will leave cluster in unusable state.
As I can see, error present on branches 3.4 and 3.5.
I think, this error can be fixed by configurable number of retries(instead of
hard-coded value of 3).
Other way to fix this is removing of max retries at all. Currently, ZK server
only stop leader election listener and continue to serve on other ports. May
be, if leader election halts, we should abort process.
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