Hi Thunder,
Can you please take and attach a thread dump with this?
Thanks,
Prateek
On Fri, Mar 16, 2018 at 4:47 PM, Thunder Stumpges <tstump...@ntent.com>
wrote:
> It appears it IS hung while serializing the JobModel... very strange! I
> added some debug statements around the calls:
>
> LOG.debug("Getting object mapper to serialize job model"); // this
> IS printed
> ObjectMapper mmapper = SamzaObjectMapper.getObjectMapper();
> LOG.debug("Serializing job model"); // this IS printed
> String jobModelStr = mmapper.writerWithDefaultPrettyPrinter
> ().writeValueAsString(jobModel);
> LOG.info("jobModelAsString=" + jobModelStr); // this is NOT printed!
>
> Another thing I noticed is that "getObjectMapper" actually creates the
> object mapper twice!
>
> 2018-03-16 23:09:24 logback 24985 [debounce-thread-0] DEBUG
> org.apache.samza.zk.ZkUtils - Getting object mapper to serialize job model
> 2018-03-16 23:09:24 logback 24994 [debounce-thread-0] DEBUG
> o.a.s.s.model.SamzaObjectMapper
> - Creating new object mapper and simple module
> 2018-03-16 23:09:24 logback 25178 [debounce-thread-0] DEBUG
> o.a.s.s.model.SamzaObjectMapper
> - Adding SerDes and mixins
> 2018-03-16 23:09:24 logback 25183 [debounce-thread-0] DEBUG
> o.a.s.s.model.SamzaObjectMapper
> - Adding custom ContainerModel deserializer
> 2018-03-16 23:09:24 logback 25184 [debounce-thread-0] DEBUG
> o.a.s.s.model.SamzaObjectMapper
> - Setting up naming strategy and registering module
> 2018-03-16 23:09:24 logback 25187 [debounce-thread-0] DEBUG
> o.a.s.s.model.SamzaObjectMapper
> - Done!
> 2018-03-16 23:09:24 logback 25187 [debounce-thread-0] DEBUG
> o.a.s.s.model.SamzaObjectMapper
> - Creating new object mapper and simple module
> 2018-03-16 23:09:24 logback 25187 [debounce-thread-0] DEBUG
> o.a.s.s.model.SamzaObjectMapper
> - Adding SerDes and mixins
> 2018-03-16 23:09:24 logback 25187 [debounce-thread-0] DEBUG
> o.a.s.s.model.SamzaObjectMapper
> - Adding custom ContainerModel deserializer
> 2018-03-16 23:09:24 logback 25187 [debounce-thread-0] DEBUG
> o.a.s.s.model.SamzaObjectMapper
> - Setting up naming strategy and registering module
> 2018-03-16 23:09:24 logback 25187 [debounce-thread-0] DEBUG
> o.a.s.s.model.SamzaObjectMapper
> - Done!
> 2018-03-16 23:09:24 logback 25187 [debounce-thread-0] DEBUG
> org.apache.samza.zk.ZkUtils - Serializing job model
>
> Could this ObjectMapper be a singleton? I see there is a private static
> instance, but getObjectMapper creates a new one every time...
>
> Anyway, then it takes off to serialize the job model and never comes
> back...
>
> Hoping someone has some idea here... the implementation for this mostly
> comes from Jackson-mapper-asl, and I have the version that is linked in the
> 0.14.0 tag:
> | | | +--- org.codehaus.jackson:jackson-mapper-asl:1.9.13
> | | | | \--- org.codehaus.jackson:jackson-core-asl:1.9.13
>
> Thanks!
> Thunder
>
> -----Original Message-----
> From: Thunder Stumpges [mailto:tstump...@ntent.com]
> Sent: Friday, March 16, 2018 15:29
> To: dev@samza.apache.org; Jagadish Venkatraman <jagadish1...@gmail.com>
> Cc: t...@recursivedream.com; yi...@linkedin.com; Yi Pan <
> nickpa...@gmail.com>
> Subject: RE: Old style "low level" Tasks with alternative deployment
> model(s)
>
> So, my investigation starts at StreamProcessor.java. Line 294 in method
> onNewJobModel() logs an INFO message that it's starting a container. This
> message never appears.
>
> I see that ZkJobCoordinator calls onNewJobModel from its
> onNewJobModelConfirmed method which also logs an info message stating
> "version X of the job model got confirmed". I never see this message
> either, so I go up the chain some more.
>
> I DO see:
>
> 2018-03-16 21:43:58 logback 20498 [ZkClient-EventThread-13-10.0.127.114:2181]
> INFO o.apache.samza.zk.ZkJobCoordinator - ZkJobCoordinator::onBecomeLeader
> - I became the leader!
> And
> 2018-03-16 21:44:18 logback 40712 [debounce-thread-0] INFO
> o.apache.samza.zk.ZkJobCoordinator -
> pid=91e07d20-ae33-4156-a5f3-534a95642133Generated
> new Job Model. Version = 1
>
> Which led me to method onDoProcessorChange line 210. I see that line, but
> not the line below " Published new Job Model. Version =" so something in
> here is not completing:
>
> LOG.info("pid=" + processorId + "Generated new Job Model. Version = "
> + nextJMVersion);
>
> // Publish the new job model
> zkUtils.publishJobModel(nextJMVersion, jobModel);
>
> // Start the barrier for the job model update
> barrier.create(nextJMVersion, currentProcessorIds);
>
> // Notify all processors about the new JobModel by updating JobModel
> Version number
> zkUtils.publishJobModelVersion(currentJMVersion, nextJMVersion);
>
> LOG.info("pid=" + processorId + "Published new Job Model. Version = "
> + nextJMVersion);
>
> As I mentioned, after the line "Generated new Job Model. Version = 1" I
> just get repeated zk ping responses.. no more application logging.
>
> The very next thing that's run is zkUtils.publishJobModel() which only has
> two lines before another log statement (which I don't see):
>
> public void publishJobModel(String jobModelVersion, JobModel jobModel) {
> try {
> ObjectMapper mmapper = SamzaObjectMapper.getObjectMapper();
> String jobModelStr = mmapper.writerWithDefaultPrettyPrinter
> ().writeValueAsString(jobModel);
> LOG.info("jobModelAsString=" + jobModelStr);
> ...
>
> Could it really be getting hung up on one of these two lines? (seems like
> it must be, but I don't see anything there that seems like it would just
> hang). I'll keep troubleshooting, maybe add some more debug logging and try
> again.
>
> Thanks for any guidance you all might have.
> -Thunder
>
>
> -----Original Message-----
> From: Thunder Stumpges [mailto:tstump...@ntent.com]
> Sent: Friday, March 16, 2018 14:43
> To: dev@samza.apache.org; Jagadish Venkatraman <jagadish1...@gmail.com>
> Cc: t...@recursivedream.com; yi...@linkedin.com; Yi Pan <
> nickpa...@gmail.com>
> Subject: RE: Old style "low level" Tasks with alternative deployment
> model(s)
>
> Well I have my stand-alone application in docker and running in
> kubernetes. I think something isn't wired up all the way though, because my
> task never actually gets invoked. I see no errors, however I'm not getting
> the usual startup logs (checking existing offsets, "entering run loop"...)
> My logs look like this:
>
> 2018-03-16 21:05:55 logback 50797 [debounce-thread-0] INFO
> kafka.utils.VerifiableProperties
> - Verifying properties
> 2018-03-16 21:05:55 logback 50797 [debounce-thread-0] INFO
> kafka.utils.VerifiableProperties
> - Property client.id is overridden to samza_admin-test_stream_task-1
> 2018-03-16 21:05:55 logback 50798 [debounce-thread-0] INFO
> kafka.utils.VerifiableProperties
> - Property metadata.broker.list is overridden to
> test-kafka-kafka.test-svc:9092
> 2018-03-16 21:05:55 logback 50798 [debounce-thread-0] INFO
> kafka.utils.VerifiableProperties
> - Property request.timeout.ms is overridden to 30000
> 2018-03-16 21:05:55 logback 50799 [debounce-thread-0] INFO
> kafka.client.ClientUtils$ - Fetching metadata from broker
> BrokerEndPoint(0,test-kafka-kafka.test-svc,9092) with correlation id 0
> for 1 topic(s) Set(dev_k8s.samza.test.topic)
> 2018-03-16 21:05:55 logback 50800 [debounce-thread-0] DEBUG
> kafka.network.BlockingChannel - Created socket with SO_TIMEOUT = 30000
> (requested 30000), SO_RCVBUF = 179680 (requested -1), SO_SNDBUF = 102400
> (requested 102400), connectTimeoutMs = 30000.
> 2018-03-16 21:05:55 logback 50800 [debounce-thread-0] INFO
> kafka.producer.SyncProducer - Connected to test-kafka-kafka.test-svc:9092
> for producing
> 2018-03-16 21:05:55 logback 50804 [debounce-thread-0] INFO
> kafka.producer.SyncProducer - Disconnecting from
> test-kafka-kafka.test-svc:9092
> 2018-03-16 21:05:55 logback 50804 [debounce-thread-0] DEBUG
> kafka.client.ClientUtils$ - Successfully fetched metadata for 1 topic(s)
> Set(dev_k8s.samza.test.topic)
> 2018-03-16 21:05:55 logback 50813 [debounce-thread-0] INFO
> o.a.s.coordinator.JobModelManager$ - SystemStreamPartitionGrouper
> org.apache.samza.container.grouper.stream.GroupByPartition@1a7158cc has
> grouped the SystemStreamPartitions into 10 tasks with the following
> taskNames: [Partition 1, Partition 0, Partition 3, Partition 2, Partition
> 5, Partition 4, Partition 7, Partition 6, Partition 9, Partition 8]
> 2018-03-16 21:05:55 logback 50818 [debounce-thread-0] INFO
> o.a.s.coordinator.JobModelManager$ - New task Partition 0 is being
> assigned changelog partition 0.
> 2018-03-16 21:05:55 logback 50819 [debounce-thread-0] INFO
> o.a.s.coordinator.JobModelManager$ - New task Partition 1 is being
> assigned changelog partition 1.
> 2018-03-16 21:05:55 logback 50820 [debounce-thread-0] INFO
> o.a.s.coordinator.JobModelManager$ - New task Partition 2 is being
> assigned changelog partition 2.
> 2018-03-16 21:05:55 logback 50820 [debounce-thread-0] INFO
> o.a.s.coordinator.JobModelManager$ - New task Partition 3 is being
> assigned changelog partition 3.
> 2018-03-16 21:05:55 logback 50820 [debounce-thread-0] INFO
> o.a.s.coordinator.JobModelManager$ - New task Partition 4 is being
> assigned changelog partition 4.
> 2018-03-16 21:05:55 logback 50820 [debounce-thread-0] INFO
> o.a.s.coordinator.JobModelManager$ - New task Partition 5 is being
> assigned changelog partition 5.
> 2018-03-16 21:05:55 logback 50820 [debounce-thread-0] INFO
> o.a.s.coordinator.JobModelManager$ - New task Partition 6 is being
> assigned changelog partition 6.
> 2018-03-16 21:05:55 logback 50820 [debounce-thread-0] INFO
> o.a.s.coordinator.JobModelManager$ - New task Partition 7 is being
> assigned changelog partition 7.
> 2018-03-16 21:05:55 logback 50820 [debounce-thread-0] INFO
> o.a.s.coordinator.JobModelManager$ - New task Partition 8 is being
> assigned changelog partition 8.
> 2018-03-16 21:05:55 logback 50820 [debounce-thread-0] INFO
> o.a.s.coordinator.JobModelManager$ - New task Partition 9 is being
> assigned changelog partition 9.
> 2018-03-16 21:05:55 logback 50838 [main-SendThread(10.0.127.114:2181)]
> DEBUG org.apache.zookeeper.ClientCnxn - Reading reply
> sessionid:0x1622c8b5fc01ac7, packet:: clientPath:null serverPath:null
> finished:false header:: 23,4 replyHeader:: 23,14024,0 request::
> '/app-test_stream_task-1/dev_test_stream_task-1-coordinationData/
> JobModelGeneration/jobModelVersion,T response::
> ,s{13878,13878,1521234010089,1521234010089,0,0,0,0,0,0,13878}
> 2018-03-16 21:05:55 logback 50838 [debounce-thread-0] INFO
> o.apache.samza.zk.ZkJobCoordinator -
> pid=a14a0434-a238-4ff6-935b-c78d906fe80dGenerated
> new Job Model. Version = 1
> 2018-03-16 21:06:05 logback 60848 [main-SendThread(10.0.127.114:2181)]
> DEBUG org.apache.zookeeper.ClientCnxn - Got ping response for sessionid:
> 0x1622c8b5fc01ac7 after 2ms
> 2018-03-16 21:06:15 logback 70856 [main-SendThread(10.0.127.114:2181)]
> DEBUG org.apache.zookeeper.ClientCnxn - Got ping response for sessionid:
> 0x1622c8b5fc01ac7 after 1ms
> 2018-03-16 21:06:25 logback 80865 [main-SendThread(10.0.127.114:2181)]
> DEBUG org.apache.zookeeper.ClientCnxn - Got ping response for sessionid:
> 0x1622c8b5fc01ac7 after 2ms ...
>
> The zk ping responses continue every 10 seconds, but no other activity or
> messages occur.
> It looks like it gets as far as confirming the JobModel and grouping the
> partitions, but nothing actually starts up.
>
> Any ideas?
> Thanks in advance!
> Thunder
>
>
> -----Original Message-----
> From: Thunder Stumpges [mailto:tstump...@ntent.com]
> Sent: Thursday, March 15, 2018 16:35
> To: Jagadish Venkatraman <jagadish1...@gmail.com>
> Cc: dev@samza.apache.org; t...@recursivedream.com; yi...@linkedin.com; Yi
> Pan <nickpa...@gmail.com>
> Subject: RE: Old style "low level" Tasks with alternative deployment
> model(s)
>
> Thanks a lot for the info. I have something basically working at this
> point! I have not integrated it with Docker nor Kubernetes yet, but it does
> run from my local machine.
>
> I have determined that LocalApplicationRunner does NOT do config
> rewriting. I had to write my own little “StandAloneApplicationRunner” that
> handles the “main” entrypoint. It does command parsing using CommandLine,
> load config from ConfigFactory, and perform rewriting before creating the
> new instance of LocalApplicationRunner. This is all my
> StandAloneApplicationRunner contains:
>
>
> object StandAloneSamzaRunner extends App with LazyLogging {
>
> // parse command line args just like JobRunner.
> val cmdline = new ApplicationRunnerCommandLine
> val options = cmdline.parser.parse(args: _*)
> val config = cmdline.loadConfig(options)
>
> val runner = new LocalApplicationRunner(Util.rewriteConfig(config))
> runner.runTask()
> runner.waitForFinish()
> }
>
> The only config settings I needed to make to use this runner were (easily
> configured due to our central Consul config system and our rewriter) :
>
> # use the ZK based job coordinator
> job.coordinator.factory=org.apache.samza.zk.ZkJobCoordinatorFactory
> # need to use GroupByContainerIds instead of GroupByContainerCount
> task.name.grouper.factory=org.apache.samza.container.grouper.task.
> GroupByContainerIdsFactory
> # ZKJC config
> job.coordinator.zk.connect=<our_zk_connection>
>
> I did run into one potential problem; as you see above, I have started the
> task using runTask() and then to prevent my main method from returning, I
> have called waitForFinish(). The first time I ran it, the job itself failed
> because I had forgotten to override the task grouper, and container count
> was pulled from our staging environment. There are some failures logged and
> it appears the JobCoordinator fails, but it never returns from
> waitForFinish. Stack trace and continuation of log is below:
>
> 2018-03-15 22:34:32 logback 77786 [debounce-thread-0] ERROR
> o.a.s.zk.ScheduleAfterDebounceTime
> - Execution of action: OnProcessorChange failed.
> java.lang.IllegalArgumentException: Your container count (4) is larger
> than your task count (2). Can't have containers with nothing to do, so
> aborting.
> at org.apache.samza.container.grouper.task.GroupByContainerCount.
> validateTasks(GroupByContainerCount.java:212)
> at org.apache.samza.container.grouper.task.
> GroupByContainerCount.group(GroupByContainerCount.java:62)
> at org.apache.samza.container.grouper.task.TaskNameGrouper.
> group(TaskNameGrouper.java:56)
> at org.apache.samza.coordinator.JobModelManager$.readJobModel(
> JobModelManager.scala:266)
> at org.apache.samza.coordinator.JobModelManager.readJobModel(
> JobModelManager.scala)
> at org.apache.samza.zk.ZkJobCoordinator.generateNewJobModel(
> ZkJobCoordinator.java:306)
> at org.apache.samza.zk.ZkJobCoordinator.doOnProcessorChange(
> ZkJobCoordinator.java:197)
> at org.apache.samza.zk.ZkJobCoordinator$LeaderElectorListenerImpl.
> lambda$onBecomingLeader$0(ZkJobCoordinator.java:318)
> at org.apache.samza.zk.ScheduleAfterDebounceTime.
> lambda$getScheduleableAction$0(ScheduleAfterDebounceTime.java:134)
> at java.util.concurrent.Executors$RunnableAdapter.
> call$$$capture(Executors.java:511)
> at java.util.concurrent.Executors$RunnableAdapter.
> call(Executors.java)
> at java.util.concurrent.FutureTask.run$$$capture(
> FutureTask.java:266)
> at java.util.concurrent.FutureTask.run(FutureTask.java)
> at java.util.concurrent.ScheduledThreadPoolExecutor$
> ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
> at java.util.concurrent.ScheduledThreadPoolExecutor$
> ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
> at java.util.concurrent.ThreadPoolExecutor.runWorker(
> ThreadPoolExecutor.java:1142)
> at java.util.concurrent.ThreadPoolExecutor$Worker.run(
> ThreadPoolExecutor.java:617)
> at java.lang.Thread.run(Thread.java:745)
> 2018-03-15 22:34:32 logback 77787 [debounce-thread-0] DEBUG
> o.a.samza.processor.StreamProcessor - Container is not instantiated yet.
> 2018-03-15 22:34:32 logback 77787 [debounce-thread-0] DEBUG
> org.I0Itec.zkclient.ZkClient - Closing ZkClient...
> 2018-03-15 22:34:32 logback 77789 [ZkClient-EventThread-15-10.0.127.114:2181]
> INFO org.I0Itec.zkclient.ZkEventThread - Terminate ZkClient event thread.
>
> And then the application continues on with metric reporters, and other
> debug logging (not actually running the task though)
>
> Thanks in advance for the guidance, this has been easier than I imagined!
> I’ll report back when I get more of the Dockerization/Kubernetes running
> and test it a bit more.
> Cheers,
> Thunder
>
>
> From: Jagadish Venkatraman [mailto:jagadish1...@gmail.com]
> Sent: Thursday, March 15, 2018 14:46
> To: Thunder Stumpges <tstump...@ntent.com>
> Cc: dev@samza.apache.org; t...@recursivedream.com; yi...@linkedin.com; Yi
> Pan <nickpa...@gmail.com>
> Subject: Re: Old style "low level" Tasks with alternative deployment
> model(s)
>
> >> Thanks for the info on the tradeoffs. That makes a lot of sense. I am
> on-board with using ZkJobCoordinator, sounds like some good benefits over
> just the Kafka high-level consumer.
>
> This certainly looks like the simplest alternative.
>
> For your other questions, please find my answers inline.
>
> >> Q1: If I use LocalApplicationRunner, It does not use
> "ProcessJobFactory" (or any StreamJob or *Job classes) correct?
>
> Your understanding is correct. It directly instantiates the
> StreamProcessor, which in-turn creates and runs the SamzaContainer.
>
> >> Q2: If I use LocalApplicationRunner, I will need to code myself the
> loading and rewriting of the Config that is currently handled by JobRunner,
> correct?
>
> I don't think you'll need to do this. IIUC, the LocalApplicationRunner
> should automatically invoke rewriters and do the right thing.
>
> >> Q3: Do I need to also handle coordinator stream(s) and storing of
> config that is done in JobRunner (I don’t think so as the ?
>
> I don't think this is necessary either. The creation of coordinator stream
> and persisting configuration happens in the LocalApplicationRunner (more
> specifically in StreamManager#createStreams).
>
> >> Q4: Where/How do I specify the Container ID for each instance? Is there
> a config setting that I can pass, (or pull from an env variable and add to
> the config) ? I am assuming it is my responsibility to ensure that each
> instance is started with a unique container ID..?
>
> Nope, If you are using the ZkJobCoordinator, you need not have to worry
> about assigning IDs for each instance. The framework will automatically
> take care of generating IDs and reaching consensus by electing a leader. If
> you are curious please take a look at implementations of the
> ProcessorIdGenerator interface.
>
> Please let us know should you have further questions!
>
> Best,
> Jagdish
>
> On Thu, Mar 15, 2018 at 11:48 AM, Thunder Stumpges <tstump...@ntent.com
> <mailto:tstump...@ntent.com>> wrote:
>
> Thanks for the info on the tradeoffs. That makes a lot of sense. I am
> on-board with using ZkJobCoordinator, sounds like some good benefits over
> just the Kafka high-level consumer.
>
>
>
> To that end, I have made some notes on possible approaches based on the
> previous thread, and from my look into the code. I’d love to get feedback.
>
>
>
> Approach 1. Configure jobs to use “ProcessJobFactory” and run instances of
> the job using run-job.sh or using JobRunner directly.
>
> I don’t think this makes sense from what I can see for a few reasons:
>
> * JobRunner is concerned with stuff I don't *think* we need:
>
> * coordinatorSystemProducer|Consumer,
> * writing/reading the configuration to the coordinator streams
>
> * ProcessJobFactory hard-codes the ID to “0” so I don’t think that
> will work for multiple instances.
>
>
>
> Approach 2. Configure ZkJobCoordinator, GroupByContainerIds, and invoke
> LocalApplicationRunner.runTask()
>
>
>
> Q1: If I use LocalApplicationRunner, It does not use
> "ProcessJobFactory" (or any StreamJob or *Job classes) correct?
>
> Q2: If I use LocalApplicationRunner, I will need to code myself the
> loading and rewriting of the Config that is currently handled by JobRunner,
> correct?
>
> Q3: Do I need to also handle coordinator stream(s) and storing of
> config that is done in JobRunner (I don’t think so as the ?
>
> Q4: Where/How do I specify the Container ID for each instance? Is
> there a config setting that I can pass, (or pull from an env variable and
> add to the config) ? I am assuming it is my responsibility to ensure that
> each instance is started with a unique container ID..?
>
> I am getting started on the above (Approach 2.), and looking closer at the
> code so I may have my own answers to my questions, but figured I should go
> ahead and ask now anyway. Thanks!
>
> -Thunder
>
>
> From: Jagadish Venkatraman [mailto:jagadish1...@gmail.com<mailto:
> jagadish1...@gmail.com>]
> Sent: Thursday, March 15, 2018 1:41
> To: dev@samza.apache.org<mailto:dev@samza.apache.org>; Thunder Stumpges <
> tstump...@ntent.com<mailto:tstump...@ntent.com>>; t...@recursivedream.com
> <mailto:t...@recursivedream.com>
> Cc: yi...@linkedin.com<mailto:yi...@linkedin.com>; Yi Pan <
> nickpa...@gmail.com<mailto:nickpa...@gmail.com>>
>
> Subject: Re: Old style "low level" Tasks with alternative deployment
> model(s)
>
> >> You are correct that this is focused on the higher-level API but
> >> doesn't
> preclude using the lower-level API. I was at the same point you were not
> long ago, in fact, and had a very productive conversation on the list
>
> Thanks Tom for linking the thread, and I'm glad that you were able to get
> Kubernetes integration working with Samza.
>
> >> If it is helpful for everyone, once I get the low-level API +
> >> ZkJobCoordinator + Docker +
> K8s working, I'd be glad to formulate an additional sample for hello-samza.
>
> @Thunder Stumpges:
> We'd be thrilled to receive your contribution. Examples, demos, tutorials
> etc.
> contribute a great deal to improving the ease of use of Apache Samza. I'm
> happy to shepherd design discussions/code-reviews in the open-source
> including answering any questions you may have.
>
>
> >> One thing I'm still curious about, is what are the drawbacks or
> >> complexities of leveraging the Kafka High-level consumer +
> >> PassthroughJobCoordinator in a stand-alone setup like this? We do
> >> have Zookeeper (because of kafka) so I think either would work. The
> >> Kafka High-level consumer comes with other nice tools for monitoring
> >> offsets, lag, etc
>
>
> @Thunder Stumpges:
>
> Samza uses a "Job-Coordinator" to assign your input-partitions among the
> different instances of your application s.t. they don't overlap. A typical
> way to solve this "partition distribution"
> problem is to have a single instance elected as a "leader" and have the
> leader assign partitions to the group.
> The ZkJobCoordinator uses Zk primitives to achieve this, while the YarnJC
> relies on Yarn's guarantee that there will be a singleton-AppMaster to
> achieve this.
>
> A key difference that separates the PassthroughJC from the Yarn/Zk
> variants is that it does _not_ attempt to solve the "partition
> distribution" problem. As a result, there's no leader-election involved.
> Instead, it pushes the problem of "partition distribution" to the
> underlying consumer.
>
> The PassThroughJc supports these 2 scenarios:
>
> 1. Consumer-managed partition distribution: When using the Kafka
> high-level consumer (or an AWS KinesisClientLibrary consumer) with Samza,
> the consumer manages partitions internally.
>
> 2. Static partition distribution: Alternately, partitions can be managed
> statically using configuration. You can achieve static partition assignment
> by implementing a custom SystemStreamPartitionGrouper<h
> ttps://samza.apache.org/learn/documentation/0.8/api/
> javadocs/org/apache/samza/container/grouper/stream/
> SystemStreamPartitionGrouper.html> and TaskNameGrouper<https://
> github.com/apache/samza/blob/master/samza-core/src/main/
> java/org/apache/samza/container/grouper/task/TaskNameGrouper.java>.
> Solutions in this category will typically require you to distinguish the
> various processors in the group by providing an "id" for each.
> Once the "id"s are decided, you can then statically compute assignments
> using a function (eg: modulo N).
> You can rely on the following mechanisms to provide this id:
> - Configure each instance differently to have its own id
> - Obtain the id from the cluster-manager. For instance, Kubernetes will
> provide each POD an unique id in the range [0,N). AWS ECS should expose
> similar capabilities via a REST end-point.
>
> >> One thing I'm still curious about, is what are the drawbacks or
> complexities of leveraging the Kafka High-level consumer +
> PassthroughJobCoordinator in a stand-alone setup like this?
>
> Leveraging the Kafka High-level consumer:
>
> The Kafka high-level consumer is not integrated into Samza just yet.
> Instead, Samza's integration with Kafka uses the low-level consumer because
> i) It allows for greater control in fetching data from individual brokers.
> It is simple and performant in-terms of the threading model to have
> one-thread pull from each broker.
> ii) It is efficient in memory utilization since it does not do
> internal-buffering of messages.
> iii) There's no overhead like Kafka-controller heart-beats that are driven
> by consumer.poll
>
> Since there's no built-in integration, you will have to build a new
> SystemConsumer if you need to integrate with the Kafka High-level consumer.
> Further, there's more a fair bit of complexity to manage in checkpointing.
>
> >> The Kafka High-level consumer comes with other nice tools for
> >> monitoring offsets, lag, etc
>
> Samza exposes<https://github.com/apache/samza/blob/master/
> samza-kafka/src/main/scala/org/apache/samza/system/kafka/
> KafkaSystemConsumerMetrics.scala> the below metrics for lag-monitoring:
> - The current log-end offset for each partition
> - The last check-pointed offset for each partition
> - The number of messages behind the highwatermark of the partition
>
> Please let us know if you need help discovering these or integrating these
> with other systems/tools.
>
>
> Leveraging the Passthrough JobCoordinator:
>
> It's helpful to split this discussion on tradeoffs with PassthroughJC into
> 2 parts:
>
> 1. PassthroughJC + consumer managed partitions:
>
> - In this model, Samza has no control over partition-assignment since it's
> managed by the consumer. This means that stateful operations like joins
> that rely on partitions being co-located on the same task will not work.
> Simple stateless operations (eg: map, filter, remote lookups) are fine.
>
> - A key differentiator between Samza and other frameworks is our support
> for "host affinity<https://samza.apache.org/learn/documentation/0.14/
> yarn/yarn-host-affinity.html>". Samza achieves this by assigning
> partitions to hosts taking data-locality into account. If the consumer can
> arbitrarily shuffle partitions, it'd be hard to support this
> affinity/locality. Often this is a key optimization when dealing with large
> stateful jobs.
>
> 2. PassthroughJC + static partitions:
>
> - In this model, it is possible to make stateful processing (including
> host affinity) work by carefully choosing how "id"s are assigned and
> computed.
>
> Recommendation:
>
> - Owing to the above subtleties, I would recommend that we give the
> ZkJobCoordinator + the built-in low-level Kafka integration a try.
> - If we hit snags down this path, we can certainly explore the approach
> with PassthroughJC + static partitions.
> - Using the PassthroughJC + consumer-managed distribution would be least
> preferable owing to the subtleties I outlined above.
>
> Please let us know should you have more questions.
>
> Best,
> Jagdish
>
> On Wed, Mar 14, 2018 at 9:24 PM, Thunder Stumpges <tstump...@ntent.com
> <mailto:tstump...@ntent.com>> wrote:
> Wow, what great timing, and what a great thread! I definitely have some
> good starters to go off of here.
>
> If it is helpful for everyone, once I get the low-level API +
> ZkJobCoordinator + Docker + K8s working, I'd be glad to formulate an
> additional sample for hello-samza.
>
> One thing I'm still curious about, is what are the drawbacks or
> complexities of leveraging the Kafka High-level consumer +
> PassthroughJobCoordinator in a stand-alone setup like this? We do have
> Zookeeper (because of kafka) so I think either would work. The Kafka
> High-level consumer comes with other nice tools for monitoring offsets,
> lag, etc....
>
> Thanks guys!
> -Thunder
>
> -----Original Message-----
> From: Tom Davis [mailto:t...@recursivedream.com<mailto:
> t...@recursivedream.com>]
> Sent: Wednesday, March 14, 2018 17:50
> To: dev@samza.apache.org<mailto:dev@samza.apache.org>
> Subject: Re: Old style "low level" Tasks with alternative deployment
> model(s)
>
> Hey there!
>
> You are correct that this is focused on the higher-level API but doesn't
> preclude using the lower-level API. I was at the same point you were not
> long ago, in fact, and had a very productive conversation on the list:
> you should look for "Question about custom StreamJob/Factory" in the list
> archive for the past couple months.
>
> I'll quote Jagadish Venkatraman from that thread:
>
> > For the section on the low-level API, can you use
> > LocalApplicationRunner#runTask()? It basically creates a new
> > StreamProcessor and runs it. Remember to provide task.class and set it
> > to your implementation of StreamTask or AsyncStreamTask. Please note
> > that this is an evolving API and hence, subject to change.
>
> I ended up just switching to the high-level API because I don't have any
> existing Tasks and the Kubernetes story is a little more straight forward
> there (there's only one container/configuration to deploy).
>
> Best,
>
> Tom
>
> Thunder Stumpges <tstump...@ntent.com<mailto:tstump...@ntent.com>> writes:
>
> > Hi all,
> >
> > We are using Samza (0.12.0) in about 2 dozen jobs implementing several
> > processing pipelines. We have also begun a significant move of other
> > services within our company to Docker/Kubernetes. Right now our
> > Hadoop/Yarn cluster has a mix of stream and batch "Map Reduce" jobs
> (many reporting and other batch processing jobs). We would really like to
> move our stream processing off of Hadoop/Yarn and onto Kubernetes.
> >
> > When I just read about some of the new progress in .13 and .14 I got
> > really excited! We would love to have our jobs run as simple libraries
> > in our own JVM, and use the Kafka High-Level-Consumer for partition
> distribution and such. This would let us "dockerfy" our application and
> run/scale in kubernetes.
> >
> > However as I read it, this new deployment model is ONLY for the
> > new(er) High Level API, correct? Is there a plan and/or resources for
> > adapting this back to existing low-level tasks ? How complicated of a
> task is that? Do I have any other options to make this transition easier?
> >
> > Thanks in advance.
> > Thunder
>
>
>
> --
> Jagadish V,
> Graduate Student,
> Department of Computer Science,
> Stanford University
>
>
>
> --
> Jagadish V,
> Graduate Student,
> Department of Computer Science,
> Stanford University
>
