It seems I forgot to attach the full logs. They should be attached now.
From: James Bucher <jbuc...@expedia.com <mailto:jbuc...@expedia.com>>
Date: Wednesday, September 6, 2017 at 10:43 AM
To: "user@flink.apache.org <mailto:user@flink.apache.org>"
<user@flink.apache.org <mailto:user@flink.apache.org>>
Subject: Flink 1.2.1 JobManager Election Deadlock
Hey all,
Just wanted to report this for posterity in case someone else sees
something similar. We were running Flink 1.2.1 in Kubernetes. We
use an HA setup with an external Zookeeper and S3 for
checkpointing. We recently noticed a job that appears to have
deadlocked on JobManager Leader election. We think the issue
happened something like the following:
1. Job was up and running normally
2. Some cluster event caused the JobManager Pod (process) to get
restarted.
3. JobManager came up again but got stuck on LeaderElection. At
this time the JobManager UI sent back a response with "Service
temporarily unavailable due to an ongoing leader election.
Please refresh."
4. JobManager never exited this state.
5. This state persisted across Pod restarts/deletes.
In order to try to pin down this problem we brought up the Job in
another Flink Cluster and started debugging this issue. As a first
step I upped the logging level on the JobManager and applied the
change. This resulted in the following log (Full logs attached to
this email):
2017-09-05 18:50:55,072 TRACE
org.apache.flink.shaded.org.apache.curator.utils.DefaultTracerDriver
- Trace: GetDataBuilderImpl-Background - 4 ms
2017-09-05 18:50:55,075 DEBUG
org.apache.flink.runtime.jobmanager.ZooKeeperSubmittedJobGraphStore
- Received CHILD_ADDED event (path: /4e4cdc8fb8c1437c620cd4063bd265e1)
2017-09-05 18:50:55,088 DEBUG
org.apache.flink.runtime.jobmanager.ZooKeeperSubmittedJobGraphStore
- Received CHILD_ADDED event notification for job
4e4cdc8fb8c1437c620cd4063bd265e1
2017-09-05 18:50:56,072 DEBUG org.apache.zookeeper.ClientCnxn
- Reading reply sessionid:0x15e3df8b5a57b4b, packet::
clientPath:null serverPath:null finished:false header:: 1,3
replyHeader:: 1,21476396435,0 request::
'/traveler-profile.us-west-2c.test.expedia.com,F response::
s{4305881524,4305881524,1497456679255,1497456679255,0,3,0,0,0,3,21475572278}
2017-09-05 18:50:56,078 DEBUG org.apache.zookeeper.ClientCnxn
- Reading reply sessionid:0x15e3df8b5a57b4b, packet::
clientPath:null serverPath:null finished:false header:: 2,3
replyHeader:: 2,21476396435,0 request::
'/traveler-profile.us-west-2c.test.expedia.com/krazyglue,F
response::
s{4305881525,4305881525,1497456679260,1497456679260,0,1,0,0,0,1,4305881526}
2017-09-05 18:50:56,079 DEBUG org.apache.zookeeper.ClientCnxn
- Reading reply sessionid:0x15e3df8b5a57b4b, packet::
clientPath:null serverPath:null finished:false header:: 3,3
replyHeader:: 3,21476396435,0 request::
'/traveler-profile.us-west-2c.test.expedia.com/krazyglue/mip,F
response::
s{4305881526,4305881526,1497456679263,1497456679263,0,1,0,0,0,1,4305881527}
2017-09-05 18:50:56,080 DEBUG org.apache.zookeeper.ClientCnxn
- Reading reply sessionid:0x15e3df8b5a57b4b, packet::
clientPath:null serverPath:null finished:false header:: 4,3
replyHeader:: 4,21476396435,0 request::
'/traveler-profile.us-west-2c.test.expedia.com/krazyglue/mip/flink,F
response::
s{4305881527,4305881527,1497456679267,1497456679267,0,1,0,0,0,1,4305881528}
2017-09-05 18:50:56,081 DEBUG org.apache.zookeeper.ClientCnxn
- Reading reply sessionid:0x15e3df8b5a57b4b, packet::
clientPath:null serverPath:null finished:false header:: 5,3
replyHeader:: 5,21476396435,0 request::
'/traveler-profile.us-west-2c.test.expedia.com/krazyglue/mip/flink/default,F
response::
s{4305881528,4305881528,1497456679270,1497456679270,0,27,0,0,0,5,21475449005}
2017-09-05 18:50:56,085 INFO
org.apache.flink.runtime.leaderretrieval.ZooKeeperLeaderRetrievalService
- Starting ZooKeeperLeaderRetrievalService.
2017-09-05 18:50:56,087 DEBUG org.apache.zookeeper.ClientCnxn
- Reading reply sessionid:0x15e3df8b5a57b4b, packet::
clientPath:null serverPath:null finished:false header:: 6,3
replyHeader:: 6,21476396435,0 request::
'/traveler-profile.us-west-2c.test.expedia.com,F response::
s{4305881524,4305881524,1497456679255,1497456679255,0,3,0,0,0,3,21475572278}
2017-09-05 18:50:56,087 DEBUG org.apache.zookeeper.ClientCnxn
- Reading reply sessionid:0x15e3df8b5a57b4b, packet::
clientPath:null serverPath:null finished:false header:: 7,3
replyHeader:: 7,21476396435,0 request::
'/traveler-profile.us-west-2c.test.expedia.com/krazyglue,F
response::
s{4305881525,4305881525,1497456679260,1497456679260,0,1,0,0,0,1,4305881526}
2017-09-05 18:50:56,088 DEBUG org.apache.zookeeper.ClientCnxn
- Reading reply sessionid:0x15e3df8b5a57b4b, packet::
clientPath:null serverPath:null finished:false header:: 8,3
replyHeader:: 8,21476396435,0 request::
'/traveler-profile.us-west-2c.test.expedia.com/krazyglue/mip,F
response::
s{4305881526,4305881526,1497456679263,1497456679263,0,1,0,0,0,1,4305881527}
2017-09-05 18:50:56,090 DEBUG org.apache.zookeeper.ClientCnxn
- Reading reply sessionid:0x15e3df8b5a57b4b, packet::
clientPath:null serverPath:null finished:false header:: 9,3
replyHeader:: 9,21476396435,0 request::
'/traveler-profile.us-west-2c.test.expedia.com/krazyglue/mip/flink,F
response::
s{4305881527,4305881527,1497456679267,1497456679267,0,1,0,0,0,1,4305881528}
2017-09-05 18:50:56,091 DEBUG org.apache.zookeeper.ClientCnxn
- Reading reply sessionid:0x15e3df8b5a57b4b, packet::
clientPath:null serverPath:null finished:false header:: 10,3
replyHeader:: 10,21476396435,0 request::
'/traveler-profile.us-west-2c.test.expedia.com/krazyglue/mip/flink/default,F
response::
s{4305881528,4305881528,1497456679270,1497456679270,0,27,0,0,0,5,21475449005}
2017-09-05 18:50:56,092 DEBUG org.apache.zookeeper.ClientCnxn
- Reading reply sessionid:0x15e3df8b5a57b4b, packet::
clientPath:/traveler-profile.us-west-2c.test.expedia.com/krazyglue/mip/flink/default/leader
serverPath:/traveler-profile.us-west-2c.test.expedia.com/krazyglue/mip/flink/default/leader
finished:false header:: 11,3 replyHeader:: 11,21476396435,0
request::
'/traveler-profile.us-west-2c.test.expedia.com/krazyglue/mip/flink/default/leader,T
response::
s{21475449005,21475449005,1503519415753,1503519415753,0,1,0,0,0,1,21475449006}
2017-09-05 18:50:56,092 TRACE
org.apache.flink.shaded.org.apache.curator.utils.DefaultTracerDriver
- Trace: ExistsBuilderImpl-Background - 1 ms
2017-09-05 18:50:56,093 DEBUG org.apache.zookeeper.ClientCnxn
- Reading reply sessionid:0x15e3df8b5a57b4b, packet::
clientPath:/traveler-profile.us-west-2c.test.expedia.com/krazyglue/mip/flink/default/leader
serverPath:/traveler-profile.us-west-2c.test.expedia.com/krazyglue/mip/flink/default/leader
finished:false header:: 12,4 replyHeader:: 12,21476396435,0
request::
'/traveler-profile.us-west-2c.test.expedia.com/krazyglue/mip/flink/default/leader,T
response::
,s{21475449005,21475449005,1503519415753,1503519415753,0,1,0,0,0,1,21475449006}
2017-09-05 18:50:56,093 TRACE
org.apache.flink.shaded.org.apache.curator.utils.DefaultTracerDriver
- Trace: GetDataBuilderImpl-Background - 1 ms
2017-09-05 18:50:56,093 DEBUG
org.apache.flink.runtime.leaderretrieval.ZooKeeperLeaderRetrievalService
- Leader node has changed.
At this point I dug into the logs to try and see what was going
on. It quickly became apparent that this probably had something to
do with Apache Curator which Flink relies upon to do the leader
election. At this point I grabbed a dump of zookeeper using:
https://github.com/ctapmex/zkTreeUtil:
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<root
path="/traveler-profile.us-west-2c.test.expedia.com/krazyglue/mip/flink">
<zknode name="default">
<zknode name="leaderlatch">
<zknode name="00000000000000000000000000000000">
<zknode name="job_manager_lock"/>
</zknode>
<zknode ephemeral="true"
name="_c_9cd3f122-65de-40e7-8e2b-aa34e6a85b83-latch-0000000020"/>
</zknode>
<zknode name="checkpoint-counter">
<zknode name="4e4cdc8fb8c1437c620cd4063bd265e1"
value="���"/>
</zknode>
<zknode name="checkpoints">
<zknode name="4e4cdc8fb8c1437c620cd4063bd265e1"/>
</zknode>
<zknode name="jobgraphs">
<zknode name="4e4cdc8fb8c1437c620cd4063bd265e1"
value="���sr�;org.apache.flink.runtime.state.RetrievableStreamStateHandle��U�+�L�wrappedStreamStateHandlet�2Lorg/apache/flink/runtime/state/StreamStateHandle;xpsr�9org.apache.flink.runtime.state.filesystem.FileStateHandle�u�b���J�	stateSizeL�filePatht�Lorg/apache/flink/core/fs/Path;xp�����h�sr�org.apache.flink.core.fs.Path��������L�urit�Ljava/net/URI;xpsr�java.net.URI�x.C�I��L�stringt�Ljava/lang/String;xpt��s3a://ewetest-traveler-profile/client-state/krazyglue/traveler-profile.us-west-2c.test.expedia.com/krazyglue/mip/flink/zookeeperCheckpoints/submittedJobGraph6507f982fe76x"/>
</zknode>
<zknode name="leader">
<zknode name="00000000000000000000000000000000"/>
</zknode>
</zknode>
</root>
In a healthy cluster there is generally a node under
“job_manager_lock” which represents the elected leader. This
pointed to a problem with the Apache Curator framework. I opened
up both Flink 1.2. And 1.3.2 to see what version of Curator Flink
1.2.1 and 1.3.2 used. I noticed that Flink 1.3.2 uses Curator
2.12.0 whereas Flink 1.2.1 uses 2.8.0. Looking at the release
notes for curator there were quite a few bugs might be the cause
of this (https://issues.apache.org/jira/browse/CURATOR-264 for
example). I was curious to see if leader election would become
unstuck if the cluster was upgraded to Flink 1.3.2. I upgraded the
JobManager to 1.3.2 and sure enough leader election proceeded
correctly. Upon Upgrading the TaskManagers the job restored from
its last checkpoint correctly and continued.
Other interesting things of note:
1. Restarting/Killing the JobManager didn’t resolve the issue. I
suspect this is due to bad state in zookeeper
2. Zookeeper was running throughout this time. We didn’t see
issues in our kafka cluster and Zookeeper has a leader elected
correctly and the Zookeeper command line utility worked
without issue.
3. Restarts of the JobManager appeared to correctly create
ephemeral nodes in zookeeper to represent possible leaders
(which also appear to get cleaned up correctly).
As far as I can tell this issue is resolved with the newer Apache
Curator version in 1.3.2. It may be useful to keep an eye out for
this issue however.
Thanks,
James Bucher
