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From Jordan Zimmerman <jor...@jordanzimmerman.com>
Subject Re: Persistent Ephemeral Node
Date Wed, 14 Oct 2015 22:51:18 GMT
Store your PEMs in a known path. Or, store a known value in the node.

-JZ

> On Oct 14, 2015, at 5:49 PM, Vikrant Singh <vikrant.subscribe@gmail.com> wrote:
> 
> 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 <mailto: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 <mailto: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 <mailto: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 <mailto: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 <mailto: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 <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 <mailto:mckenzie.cam@gmail.com>]

> Sent: Monday, October 12, 2015 5:05 PM
> To: user@curator.apache.org <mailto: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 <mailto: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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