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From Vikrant Singh <vikrant.subscr...@gmail.com>
Subject Re: Persistent Ephemeral Node
Date Wed, 14 Oct 2015 22:49:53 GMT
What I  want is to differentiate between "ephemeral nodes" and "persistent
ephemeral node".

On Wed, Oct 14, 2015 at 3:20 PM, Cameron McKenzie <mckenzie.cam@gmail.com>
wrote:

> You could keep track of which nodes are ephemeral by looking at the stat
> object passed to the NODE_ADDED event in the TreeCache. Then when you get a
> NODE_REMOVED event you could check if it's one of your ephemeral nodes?
>
> On Thu, Oct 15, 2015 at 4:06 AM, Vikrant Singh <
> vikrant.subscribe@gmail.com> wrote:
>
>> yes you got it correct... a slight correction. I am trying to find a way
>> where I can make my tree cache event handler aware that "node removed"
>> event is coming from a persistent ephemeral node  and delay any action till
>> the point the node's curator framework gives up on rewriting the node to ZK.
>>
>> On Mon, Oct 12, 2015 at 3:38 PM, Cameron McKenzie <mckenzie.cam@gmail.com
>> > wrote:
>>
>>> So, if I'm understanding correctly, if your application loses its
>>> connection to ZooKeeper (or crashes), then a new instance will be started
>>> in its place, and if the original instance reconnects then you don't want
>>> it to try and recreate its ephemeral node?
>>>
>>> If that's the case, then I think that you need additional logic beyond
>>> what a PersistentEphemeralNode is going to provide you, as you will need to
>>> check if the node already exists on reconnection.
>>>
>>> On Tue, Oct 13, 2015 at 8:43 AM, Vikrant Singh <
>>> vikrant.subscribe@gmail.com> wrote:
>>>
>>>> yeah I considered that.. but I ended up using tree cache because it
>>>> gives me more control on the state of tree . I have some custom handlers
>>>> for add/remove/update events. Same cache is also used for service discovery.
>>>>
>>>> On Mon, Oct 12, 2015 at 2:33 PM, David Kesler <DKesler@yodle.com>
>>>> wrote:
>>>>
>>>>> There’s also already a Curator service discovery extension library
>>>>> that you can look at:
>>>>> http://curator.apache.org/curator-x-discovery/index.html.  It’s
>>>>> basically boiling down to the same strategy of sticking an ephemeral
node
>>>>> into ZK, but with some additional convenience and functionality built
on
>>>>> top of it.
>>>>>
>>>>>
>>>>>
>>>>> *From:* Cameron McKenzie [mailto:mckenzie.cam@gmail.com]
>>>>> *Sent:* Monday, October 12, 2015 5:05 PM
>>>>> *To:* user@curator.apache.org
>>>>> *Subject:* Re: Persistent Ephemeral Node
>>>>>
>>>>>
>>>>>
>>>>> hey Vikrant,
>>>>>
>>>>> Using a persistent ephemeral node just means that your application
>>>>> code doesn't need to worry about handling recreation of the node when
it
>>>>> reconnects to ZooKeeper after connection / session loss.
>>>>>
>>>>>
>>>>>
>>>>> If your ephemeral node should always be present whenever your
>>>>> application instance is running, then this would be a good use case for
a
>>>>> persistent ephemeral node.
>>>>>
>>>>> cheers
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Tue, Oct 13, 2015 at 6:03 AM, Vikrant Singh <
>>>>> vikrant.subscribe@gmail.com> wrote:
>>>>>
>>>>> I have some basic question on persistent ephemeral node.
>>>>>
>>>>> Here is some background...
>>>>>
>>>>>
>>>>>
>>>>> We have a zoo keeper based service discovery setup. Each service
>>>>> register itself as a ephemeral node with zookeeper.When a service go
down
>>>>>  its ephemeral node is removed from zookeeper and we know that service
is
>>>>> down and we provision it again.
>>>>>
>>>>> At present we create plain ephemeral node. I am wondering what
>>>>> benefit/risks we may get if move to persistent ephemeral ones.  I see
one
>>>>> problem... using  plane ephemeral node we can rely on state of ZK to
make a
>>>>> decision like service is down. This is because we are sure that if a
node
>>>>> get deleted with zoo keeper it will never comeback from same process.
But
>>>>> if moved to "persistent ephemeral" I guess same may not be the case.
>>>>>
>>>>>
>>>>>
>>>>> Please let me know what you think of the same.
>>>>>
>>>>>
>>>>>
>>>>> Also I would like to know what are the best scenario where one should
>>>>> prefer using persistent ephemeral node over ephemeral node.
>>>>>
>>>>>
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Vikrant
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>
>>
>

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