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From Cameron McKenzie <mckenzie....@gmail.com>
Subject Re: Persistent Ephemeral Node
Date Mon, 12 Oct 2015 22:38:50 GMT
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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