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From Moshiko Kasirer <mos...@liveperson.com>
Subject Re: question about curator - retry policy
Date Fri, 20 May 2016 22:42:31 GMT
Thanks for the answers it helped a lot! Last question please what triggers
the Clint to always try to reconnect the zk cluster those 30 minutes (from
my example above) I mean the connections are lost etc so what will trigger
the reestablish of the connection when zk is available again?
בתאריך 21 במאי 2016 01:36,‏ "Moshiko Kasirer" <moshek@liveperson.com> כתב:

> We are using nginx as our web tier which delegate requests to app nodes
> using consistent hashing to one of the registered app nodes. Since we have
> many web and app nodes we have to make sure all available app nodes are
> known to the web tier and that in any given time they all see the same app
> nodes picture. So we built an app on top of your service discovery that
> when app node ris up he register and web tier is listening to that cluster
> and changes his available app nodes view.In adoption we handle situations
> when there is on connection to zk using a cache file with latest available
> view until the connection is restored. For some reason sometimes although
> zk is up and running the curator connection to which we listen to know if
> we should reregister isn't invoked meaning stays as LOST...
> בתאריך 21 במאי 2016 01:23,‏ "Jordan Zimmerman" <jordan@jordanzimmerman.com>
> כתב:
>
>> Retry policy is only used for individual operations. Any client-server
>> system needs to have retries to avoid temporary network events. The entire
>> curator-client and curator-framework modules are written to handle
>> ZooKeeper client connection maintenance. So, there isn’t one thing I can
>> point to.
>>
>> Internally, the ServiceDiscovery code uses a PathChildrenCache instance.
>> If all you are using is Service Discovery there is almost no need for you
>> to monitor the connection state. What are you trying to accomplish?
>>
>> -Jordan
>>
>> On May 20, 2016, at 5:19 PM, Moshiko Kasirer <moshek@liveperson.com>
>> wrote:
>>
>> The thing is we have many negative tests in which we stop and start the
>> zk quorum the issue I raised only happens from time to time.... So it's hat
>> I hard to reproduce. But you just wrote that when the quorom is up the
>> connection should be reconnected ... how? who does that? ZkClient  or
>> curator? That is not related to retry policy?
>> בתאריך 21 במאי 2016 01:12,‏ "Jordan Zimmerman" <
>> jordan@jordanzimmerman.com> כתב:
>>
>>> If the ZK cluster’s quorum is restored, then the connection state should
>>> change to RECONNECTED. There are copious tests in Curator itself that show
>>> this. If you’re seeing that Curator does not restore a broken connection
>>> then there is a deeper bug. Can you create a test that shows the problem?
>>>
>>> -Jordan
>>>
>>> On May 20, 2016, at 5:07 PM, Moshiko Kasirer <moshek@liveperson.com>
>>> wrote:
>>>
>>> I mean that while zk cluster is up the curator connection state stays
>>> LOST
>>> Which in our case means the app node in which it happens doesnt register
>>> himself as avalable.... I just don't seem to understand when does curator
>>> gives up on trying to connect zk and when he doesn't give up.
>>> Thanks for the help !
>>> בתאריך 21 במאי 2016 00:58,‏ "Jordan Zimmerman" <
>>> jordan@jordanzimmerman.com> כתב:
>>>
>>>> You must have a retry policy so that you don’t overwhelm your network
>>>> and ZooKeeper cluster. The example code shows how to create a reasonable
>>>> one.
>>>>
>>>> sometimes although zk cluster is up the curator service discovery
>>>> connection isn't
>>>>
>>>> Service Discovery’s internal instances might be waiting based on the
>>>> retry policy. But, what do you mean by "curator service discovery
>>>> connection isn’t”? There isn’t such a thing as a service discovery
>>>> connection.
>>>>
>>>> -Jordan
>>>>
>>>> On May 20, 2016, at 4:53 PM, Moshiko Kasirer <moshek@liveperson.com>
>>>> wrote:
>>>>
>>>> We are using your service discovery. So you are saying I should not
>>>> care about the retry policy...? So the only thing left to explain is how
>>>> come sometimes although zk cluster is up the curator service discovery
>>>> connection isn't.....
>>>> בתאריך 21 במאי 2016 00:43,‏ "Jordan Zimmerman" <
>>>> jordan@jordanzimmerman.com> כתב:
>>>>
>>>> If you are using Curator’s Service Discovery code, it will be
>>>> continuously re-trying the connections. This is not because of the retry
>>>> policy it’s because the Service Discovery code manages connection
>>>> interruptions internally.
>>>>
>>>> -Jordan
>>>>
>>>> On May 20, 2016, at 4:40 PM, Moshiko Kasirer <moshek@liveperson.com>
>>>> wrote:
>>>>
>>>> Thanks for the replay I will send those logs ASAP.
>>>> It's difficult to understand the connection mechanism of zk ....
>>>> We are using curator 2.10 as our service discovery so we have to make
>>>> sure that when zk is alive we connect and inform the our server is up we
do
>>>> that by listening to curator connection listener which I think has also to
>>>> do with the retry policy.... But what I can't understand is why sometimes
>>>> we can see in the log that curator gave up (Lost) yet still a second later
>>>> curator connection is restored how? Is it because zk session heartbeat
>>>> restored the connection? Does that Iovine curator to change his connection
>>>> state? And on the other side we sometimes get to a point were zk is up but
>>>> curator connection stays as Lost...
>>>> That is why I thought of using the new always try policy you entered do
>>>> you think it can help? That why  hope there will be no way that zk is up
>>>> but curator status is lost.....as once he will retry he will reconnect to
>>>> zk.... Is that correct?
>>>> בתאריך 21 במאי 2016 00:10,‏ "Jordan Zimmerman" <
>>>> jordan@jordanzimmerman.com> כתב:
>>>>
>>>>> Curator’s retry policies are used within each CuratorFramework
>>>>> operation. For example, when you call client.setData().forPath(p, b)
the
>>>>> retry policy will be invoked if there is a retry-able exception during
the
>>>>> operation. In addition to the retryPolicy, there are connection timeouts.
>>>>> The behavior of how this is handled changed between Curator 2.x and Curator
>>>>> 3.x. In Curator 2.x, for every iteration of the retry, the operation
will
>>>>> wait until connection timeout when there’s no connection. In Curator
3.x,
>>>>> the connection timeout wait only occurs once (if the default
>>>>> ConnectionHandlingPolicy is used).
>>>>>
>>>>> In any event, ZooKeeper itself tries to maintain the connection. Also,
>>>>> Curator will re-create the internally managed connection depending various
>>>>> network interruptions, etc. I’d need to see the logs to give you more
>>>>> input.
>>>>>
>>>>> -Jordan
>>>>>
>>>>> On May 19, 2016, at 10:12 AM, Moshiko Kasirer <moshek@liveperson.com>
>>>>> wrote:
>>>>>
>>>>> first i would like to thank you about curator we are using it as part
>>>>> of our service discovery
>>>>>
>>>>> solution and it helps a lot!!
>>>>>
>>>>> i have a question i hope you will be able to help me with.
>>>>>
>>>>> its regarding the curator retry policy it seems to me we dont really
>>>>> understand when this policy is
>>>>>
>>>>> invoked,  as i see in our logs that although i configured it as max
>>>>> retry 1 actually in the logs i see
>>>>>
>>>>> many ZK re connection attempts (and many curator gave up messages but
>>>>> later i see
>>>>>
>>>>> reconnected status...) . is it possible that that policy is only
>>>>> relevant to manually invoked
>>>>>
>>>>> operations against the ZK cluster done via curator ? and that the re
>>>>> connections i see in the logs
>>>>>
>>>>> are caused by the fact that the ZK was available during start up so
>>>>> sessions were created and
>>>>>
>>>>> then when ZK was down the ZK clients *(not curator) * are sending
>>>>> heartbeats as part of the ZK
>>>>>
>>>>> architecture? that is the part i am failing to understand and i hope
>>>>> you can help me with that.
>>>>>
>>>>> you have recently added RetreyAllways policy and i wanted to know if
>>>>> it is save to use it?
>>>>>
>>>>> the thing is we always want to retry to reconnect to ZK when he is
>>>>> available but that is something
>>>>>
>>>>> the ZK client does as long as he has open sessions right?  i am not
>>>>> sure that it has to do with the
>>>>>
>>>>> retry policy ...
>>>>>
>>>>> thanks,
>>>>>
>>>>> moshiko
>>>>>
>>>>> --
>>>>> Moshiko Kasirer
>>>>> Software Engineer
>>>>> T: +972-74-700-4357
>>>>> <http://www.linkedin.com/company/164748>
>>>>> <http://twitter.com/liveperson>
>>>>> <http://www.facebook.com/LivePersonInc> We Create Meaningful
>>>>> Connections
>>>>> <http://roia.biz/im/n/ndiXvq1BAAGhL0MAABW7QgABwExmMQA-A/>
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