Re: TaskManager takes abnormally long time to register with JobManager on Kubernetes for Flink 1.11.0

Posted by Till Rohrmann on
URL: http://deprecated-apache-flink-user-mailing-list-archive.369.s1.nabble.com/TaskManager-takes-abnormally-long-time-to-register-with-JobManager-on-Kubernetes-for-Flink-1-11-0-tp38638p38682.html

Hi Weike,

could you try setting kubernetes.jobmanager.cpu: 4 in your flink-conf.yaml? I fear that a single CPU is too low for the JobManager component.

Cheers,

Till

On Tue, Oct 13, 2020 at 11:33 AM Till Rohrmann <[hidden email]> wrote:

Hi Weike,

thanks for posting the logs. I will take a look at them. My suspicion would be that there is some operation blocking the JobMaster's main thread which causes the registrations from the TMs to time out. Maybe the logs allow me to validate/falsify this suspicion.

Cheers,

Till

On Mon, Oct 12, 2020 at 10:43 AM DONG, Weike <[hidden email]> wrote:

Hi community,

I have uploaded the log files of JobManager and TaskManager-1-1 (one of the 50 TaskManagers) with DEBUG log level and default Flink configuration, and it clearly shows that TaskManager failed to register with JobManager after 10 attempts.

Here is the link:

JobManager: 

https://gist.github.com/kylemeow/740c470d9b5a1ab3552376193920adce

TaskManager-1-1: 

https://gist.github.com/kylemeow/41b9a8fe91975875c40afaf58276c2fe  

Thanks : )

Best regards,

Weike

On Mon, Oct 12, 2020 at 4:14 PM DONG, Weike <[hidden email]> wrote:

Hi community,

Recently we have noticed a strange behavior for Flink jobs on Kubernetes per-job mode: when the parallelism increases, the time it takes for the TaskManagers to register with JobManager becomes abnormally long (for a task with parallelism of 50, it could take 60 ~ 120 seconds or even longer for the registration attempt), and usually more than 10 attempts are needed to finish this registration.

Because of this, we could not submit a job requiring more than 20 slots with the default configuration, as the TaskManager would say:

 

Registration at JobManager (akka.tcp://[e-mail]:6123/user/rpc/jobmanager_2) attempt 9 timed out after 25600 ms

Free slot with allocation id 60d5277e138a94fb73fc6691557001e0 because: The slot 60d5277e138a94fb73fc6691557001e0 has timed out. 

Free slot TaskSlot(index:0, state:ALLOCATED, resource profile: ResourceProfile{cpuCores=1.0000000000000000, taskHeapMemory=1.425gb (1530082070 bytes), taskOffHeapMemory=0 bytes, managedMemory=1.340gb (1438814063 bytes), networkMemory=343.040mb (359703515 bytes)}, allocationId: 60d5277e138a94fb73fc6691557001e0, jobId: 493cd86e389ccc8f2887e1222903b5ce).
java.lang.Exception: The slot 60d5277e138a94fb73fc6691557001e0 has timed out. 

In order to cope with this issue, we have to change the below configuration parameters:

# Prevent "Could not allocate the required slot within slot request timeout. Please make sure that the cluster has enough resources. Stopping the JobMaster for job"
slot.request.timeout: 500000 

# Increase max timeout in a single attempt
cluster.registration.max-timeout: 300000
# Prevent "free slot (TaskSlot)"
akka.ask.timeout: 10 min
# Prevent "Heartbeat of TaskManager timed out."
heartbeat.timeout: 500000

However, we acknowledge that this is only a temporary dirty fix, which is not what we want. It could be seen that during TaskManager registration to JobManager, lots of warning messages come out in logs:

No hostname could be resolved for the IP address 9.166.0.118, using IP address as host name. Local input split assignment (such as for HDFS files) may be impacted.

Initially we thought this was probably the cause (reverse lookup of DNS might take up a long time), however we later found that the reverse lookup only took less than 1ms, so maybe not because of this.

Also, we have checked the GC log of both TaskManagers and JobManager, and they seem to be perfectly normal, without any signs of pauses. And the heartbeats are processed as normal according to the logs.

Moreover, TaskManagers register quickly with ResourceManager, but then extra slow with TaskManager, so this is not because of a slow network connection. 

Here we wonder what could be the cause for the slow registration between JobManager and TaskManager(s)? No other warning or error messages in the log (DEBUG level) other than the "No hostname could be resolved" messages, which is quite weird.

Thanks for the reading, and hope to get some insights into this issues : )

Sincerely,

Weike