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https://issues.apache.org/jira/browse/ZOOKEEPER-3466?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16891722#comment-16891722
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Jan-Philip Gehrcke commented on ZOOKEEPER-3466:
-----------------------------------------------
Thanks for having a look, Michael.
{quote}
is the problem being that clients can't connect to the ensemble,
{quote}
This (cf. point 6 in the description above). To clarify, the problem exists in
a freshly set up 3.5.5 ZooKeeper ensemble.
{quote}
If it's ok to disclose the log files for both server and client,
{quote}
Relevant client log is above, but let me put it into a code block with a tiny
bit more context
{code:java}
Python 3.6.8 (default, Jun 26 2019, 00:07:55)
[GCC 4.8.5] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import kazoo
>>> from kazoo.client import KazooClient
>>> zk = KazooClient(hosts='127.0.0.1:2181')
>>> zk.start()
Connection time-out: socket time-out during read
{code}
Relevant server log on TRACE level, with my annotations :
{code}
# There is a bit of history before this log snippet, but it's not much.
# It's a "fresh" ZooKeeper ensemble managed by Exhibitor.
# The current ZooKeeper instance (of which we see the logs)
# was restarted two or three times.
[...]
# Shortly before this the last leader election was triggered
# Here, the current ZooKeeper instance (of which we see the log)
# was just elected leader. It has two followers
Jul 23 14:38:07 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] INFO
[QuorumPeer[myid=3](plain=/0:0:0:0:0:0:0:0:2181)(secure=disabled):Leader@1296]
- Have quorum of supporters, sids: [ [1, 2, 3],[1, 2] ]; starting up and
setting last processed zxid: 0x200000000
Jul 23 14:38:07 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[QuorumPeer[myid=3](plain=/0:0:0:0:0:0:0:0:2181)(secure=disabled):QuorumPeer@1934]
- Reconfig feature is disabled, skip reconfig processing.
Jul 23 14:38:07 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] INFO
[QuorumPeer[myid=3](plain=/0:0:0:0:0:0:0:0:2181)(secure=disabled):CommitProcessor@256]
- Configuring CommitProcessor with 8 worker threads.
Jul 23 14:38:07 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] INFO
[QuorumPeer[myid=3](plain=/0:0:0:0:0:0:0:0:2181)(secure=disabled):ContainerManager@64]
- Using checkIntervalMs=60000 maxPerMinute=10000
Jul 23 14:38:07 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[LearnerHandler-/172.17.0.5:58670:LearnerHandler@534] - Sending UPTODATE
message to 2
Jul 23 14:38:07 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[LearnerHandler-/172.17.0.3:52126:LearnerHandler@534] - Sending UPTODATE
message to 1
Jul 23 14:38:07 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[Sender-/172.17.0.3:52126:ZooTrace@71] - o UPTODATE ffffffffffffffff null
Jul 23 14:38:07 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[Sender-/172.17.0.5:58670:ZooTrace@71] - o UPTODATE ffffffffffffffff null
Jul 23 14:38:07 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[LearnerHandler-/172.17.0.5:58670:ZooTrace@71] - i ACK 200000000 null
Jul 23 14:38:07 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[LearnerHandler-/172.17.0.3:52126:ZooTrace@71] - i ACK 200000000 null
# The local Exhibitor (supervisor of this ZK instance) sends ruok and srvr
commands
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[NIOServerCxnFactory.AcceptThread:/0.0.0.0:2181:NIOServerCnxnFactory$AcceptThread@296]
- Accepted socket connection from /127.0.0.1:37620
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] INFO
[NIOWorkerThread-3:NIOServerCnxn@518] - Processing ruok command from
/127.0.0.1:37620
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[NIOWorkerThread-3:NIOServerCnxn@627] - Closed socket connection for client
/127.0.0.1:37620 (no session established for client)
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[NIOServerCxnFactory.AcceptThread:/0.0.0.0:2181:NIOServerCnxnFactory$AcceptThread@296]
- Accepted socket connection from /127.0.0.1:37622
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] INFO
[NIOWorkerThread-4:NIOServerCnxn@518] - Processing srvr command from
/127.0.0.1:37622
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[NIOWorkerThread-4:NIOServerCnxn@627] - Closed socket connection for client
/127.0.0.1:37622 (no session established for client)
# The next log line is emitted by Exhibitor (Exhibitor and ZK logs are
interleaved),
# it confirms that Exhibitor saw expected RUOK and SRVR feedback.
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 start_exhibitor.py[1307]: INFO
com.netflix.exhibitor.core.activity.ActivityLog State: serving
[ActivityQueue-0]
# Now that Exhibitor "thinks" that ZooKeeper is healthy the ZK clients try to
connect
# (to all three nodes in the ZK ensemble).
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[LearnerHandler-/172.17.0.3:52126:ZooTrace@71] - i REQUEST ffffffffffffffff null
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[ProcessThread(sid:3 cport:-1)::ZooTrace@88] - :Psessionid:0x1000ac8b67e0000
type:createSession cxid:0x0 zxid:0xfffffffffffffffe txntype:unknown reqpath:n/a
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[ProcessThread(sid:3 cport:-1)::SessionTrackerImpl@274] - Adding session
0x1000ac8b67e0000
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[ProcessThread(sid:3 cport:-1)::ZooTrace@71] - SessionTrackerImpl --- Adding
session 0x1000ac8b67e0000 10000
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[ProcessThread(sid:3 cport:-1)::CommitProcessor@344] - Processing request::
sessionid:0x1000ac8b67e0000 type:createSession cxid:0x0 zxid:0x200000001
txntype:-10 reqpath:n/a
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[ProcessThread(sid:3 cport:-1)::Leader@1114] - Proposing::
sessionid:0x1000ac8b67e0000 type:createSession cxid:0x0 zxid:0x200000001
txntype:-10 reqpath:n/a
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] INFO
[SyncThread:3:FileTxnLog@216] - Creating new log file: log.200000001
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[LearnerHandler-/172.17.0.5:58670:ZooTrace@71] - i ACK 200000001 null
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[LearnerHandler-/172.17.0.3:52126:ZooTrace@71] - i ACK 200000001 null
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[NIOServerCxnFactory.AcceptThread:/0.0.0.0:2181:NIOServerCnxnFactory$AcceptThread@296]
- Accepted socket connection from /127.0.0.1:37630
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[NIOWorkerThread-5:ZooKeeperServer@1001] - Session establishment request from
client /127.0.0.1:37630 client's lastZxid is 0x0
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[NIOWorkerThread-5:SessionTrackerImpl@274] - Adding session 0x3000ac8b6c50000
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[NIOWorkerThread-5:ZooTrace@71] - SessionTrackerImpl --- Adding session
0x3000ac8b6c50000 10000
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[ProcessThread(sid:3 cport:-1)::ZooTrace@88] - :Psessionid:0x3000ac8b6c50000
type:createSession cxid:0x0 zxid:0xfffffffffffffffe txntype:unknown reqpath:n/a
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[ProcessThread(sid:3 cport:-1)::ZooTrace@71] - SessionTrackerImpl --- Existing
session 0x3000ac8b6c50000 10000
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[ProcessThread(sid:3 cport:-1)::CommitProcessor@344] - Processing request::
sessionid:0x3000ac8b6c50000 type:createSession cxid:0x0 zxid:0x200000002
txntype:-10 reqpath:n/a
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[ProcessThread(sid:3 cport:-1)::Leader@1114] - Proposing::
sessionid:0x3000ac8b6c50000 type:createSession cxid:0x0 zxid:0x200000002
txntype:-10 reqpath:n/a
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[NIOWorkerThread-5:ZooKeeperServer@1052] - Client attempting to establish new
session: session = 0x3000ac8b6c50000, zxid = 0x0, timeout = 10000, address =
/127.0.0.1:37630
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[LearnerHandler-/172.17.0.3:52126:ZooTrace@71] - i ACK 200000002 null
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[LearnerHandler-/172.17.0.5:58670:ZooTrace@71] - i ACK 200000002 null
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[LearnerHandler-/172.17.0.5:58670:ZooTrace@71] - i REQUEST ffffffffffffffff null
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[ProcessThread(sid:3 cport:-1)::ZooTrace@88] - :Psessionid:0x2000ac8b60f0000
type:createSession cxid:0x0 zxid:0xfffffffffffffffe txntype:unknown reqpath:n/a
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[ProcessThread(sid:3 cport:-1)::SessionTrackerImpl@274] - Adding session
0x2000ac8b60f0000
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[ProcessThread(sid:3 cport:-1)::ZooTrace@71] - SessionTrackerImpl --- Adding
session 0x2000ac8b60f0000 10000
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[ProcessThread(sid:3 cport:-1)::CommitProcessor@344] - Processing request::
sessionid:0x2000ac8b60f0000 type:createSession cxid:0x0 zxid:0x200000003
txntype:-10 reqpath:n/a
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[ProcessThread(sid:3 cport:-1)::Leader@1114] - Proposing::
sessionid:0x2000ac8b60f0000 type:createSession cxid:0x0 zxid:0x200000003
txntype:-10 reqpath:n/a
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[LearnerHandler-/172.17.0.3:52126:ZooTrace@71] - i ACK 200000003 null
Jul 23 14:38:35 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[LearnerHandler-/172.17.0.5:58670:ZooTrace@71] - i ACK 200000003 null
Jul 23 14:38:36 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[NIOServerCxnFactory.AcceptThread:/0.0.0.0:2181:NIOServerCnxnFactory$AcceptThread@296]
- Accepted socket connection from /127.0.0.1:37636
Jul 23 14:38:36 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[NIOWorkerThread-6:ZooKeeperServer@1001] - Session establishment request from
client /127.0.0.1:37636 client's lastZxid is 0x0
Jul 23 14:38:36 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[NIOWorkerThread-6:SessionTrackerImpl@274] - Adding session 0x3000ac8b6c50001
Jul 23 14:38:36 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[NIOWorkerThread-6:ZooTrace@71] - SessionTrackerImpl --- Adding session
0x3000ac8b6c50001 10000
Jul 23 14:38:36 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[ProcessThread(sid:3 cport:-1)::ZooTrace@88] - :Psessionid:0x3000ac8b6c50001
type:createSession cxid:0x0 zxid:0xfffffffffffffffe txntype:unknown reqpath:n/a
Jul 23 14:38:36 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] TRACE
[ProcessThread(sid:3 cport:-1)::ZooTrace@71] - SessionTrackerImpl --- Existing
session 0x3000ac8b6c50001 10000
Jul 23 14:38:36 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[ProcessThread(sid:3 cport:-1)::CommitProcessor@344] - Processing request::
sessionid:0x3000ac8b6c50001 type:createSession cxid:0x0 zxid:0x200000004
txntype:-10 reqpath:n/a
Jul 23 14:38:36 dcos-e2e-9af6b-master-1 java[9048]: [myid:3] DEBUG
[ProcessThread(sid:3 cport:-1)::Leader@1114] - Proposing::
sessionid:0x3000ac8b6c50001 type:createSession cxid:0x0 zxid:0x200000004
txntype:-10 reqpath:n/a
...
{code}
The server log above corresponds to client(s) not getting bytes on the TCP
connection (resulting in timeout errors).
{quote}
It would be also helpful to have a relatively straight forward reproduce steps
with detailed version and configuration information for both server and clients.
{quote}
Yes, I can imagine and I would love to be able to provide a simple repro.
However, I could only see this so far when Exhibitor coordinates ZooKeeper
through a dynamic ensemble which involves another ZooKeeper or S3. Personally I
do have a repro, but it is still too complex to share ... it involves a DC/OS
cluster started in various Docker containers and a coordination ZooKeeper
instance (through which the individual Exhibitor instances coordinate
themselves). They key insight from this repro environment is that the exact
same setup works fine with ZooKeeper 3.4.14, but breaks often (not always) with
ZooKeeper 3.5.5.
> ZK cluster converges, but does not properly handle client connections (new in
> 3.5.5)
> ------------------------------------------------------------------------------------
>
> Key: ZOOKEEPER-3466
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3466
> Project: ZooKeeper
> Issue Type: Bug
> Affects Versions: 3.5.5
> Environment: Linux
> Reporter: Jan-Philip Gehrcke
> Priority: Major
>
> Hey, we explore switching from ZooKeeper 3.4.14 to ZooKeeper 3.5.5 in
> [https://github.com/dcos/dcos].
> DC/OS coordinates ZooKeeper via Exhibitor. We are not changing anything
> w.r.t. Exhibitor for now, and are hoping that we can use ZooKeeper 3.5.5 as a
> drop-in replacement for 3.4.14. This seems to work fine when Exhibitor uses a
> so-called static ensemble where the individual ZooKeeper instances are known
> a priori.
> When Exhibitor however discovers individual ZooKeeper instances ("dynamic"
> back-end) then I think we observe a regression where ZooKeeper 3.5.5 can get
> into the following bad state (often, but not always):
> # three ZooKeeper instances find each other, leader election takes place
> (*expected*)
> # leader election succeeds: two followers, one leader (*expected*)
> # all three ZK instances respond IAMOK to RUOK (*expected*)
> # all three ZK instances respond to SRVR (one says "Mode: leader", the other
> two say "Mode: follower") (*expected*)
> # all three ZK instances respond to MNTR and show plausible output
> (*expected*)
> # *{color:#ff0000}Unexpected:{color}* any ZooKeeper client trying to connect
> to any of the three nodes observes a "connection timeout", whereas notably
> this is *not* a TCP connect() timeout. The TCP connect() succeeds, but then
> ZK does not seem to send the expected byte sequence to the TCP connection,
> and the ZK client waits for it via recv() until it hits a timeout condition.
> Examples for two different clients:
> ## In Kazoo we specifically hit _Connection time-out: socket time-out during
> read_
> generated here:
> [https://github.com/python-zk/kazoo/blob/88b657a0977161f3815657878ba48f82a97a3846/kazoo/protocol/connection.py#L249]
> ## In zkCli we see _Client session timed out, have not heard from server in
> 15003ms for sessionid 0x0, closing socket connection and attempting reconnect
> (org.apache.zookeeper.ClientCnxn:main-SendThread(localhost:2181))_
> # This state is stable, it will last forever (well, at least for multiple
> hours and we didn't test longer than that).
> # In our system the ZooKeeper clients are crash-looping. They retry. What I
> have observed is that while they retry the ZK ensemble accumulates
> outstanding requests, here shown from MNTR output (emphasis mine):
> zk_packets_received 2008
> zk_packets_sent 127
> zk_num_alive_connections 18
> zk_outstanding_requests *1880*
> # The leader emits log lines confirming session timeout, example:
> _[myid:3] INFO [SessionTracker:ZooKeeperServer@398] - Expiring session
> 0x2000642b18f0020, timeout of 10000ms exceeded [myid:3] INFO
> [SessionTracker:QuorumZooKeeperServer@157] - Submitting global closeSession
> request for session 0x2000642b18f0020_
> # In this state, restarting any one of the two ZK followers results in the
> same state (clients don't get data from ZK upon connect).
> # In this state, restarting the ZK leader, and therefore triggering a leader
> re-election, almost immediately results in all clients being able to connect
> to all ZK instances successfully.
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