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From: Alexander Shraer <shralex@gmail.com>
Date: Sat, 20 Jun 2015 19:35:46 -0700
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 <CANcXBFMiBPp7hqf8pg8aSd7r8_5b3csGLVX1=h-2diV68oHX5g@mail.gmail.com>
Subject: Re: Incrementally bootstrapping a 3.5.0-alpha cluster?
To: "user@zookeeper.apache.org" <user@zookeeper.apache.org>
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Hi,

Approach 1 isn't supposed to work, since each server forms its own
ensemble. Each server is the leader in its own ensemble
so when you try to reconfigure it expects the other server to connect as a
follower but that doesn't happen. The error just means that you can't
reconfigure since you will loose a quorum (in an ensemble of 2 servers you
must have both ack every request and here you won't have that since they
are not talking).

Approach 2 is supposed to work, no matter if the first server is 2 or 1.
There may be a bug of course, but I just locally tried the scenario that
fails for you (as I understood it) and it worked. Here is my setup, perhaps
your can send me yours if it still doesn't work.

server 1:
dataDir=/home/shralex/zk-sat/zookeeper1
standaloneEnabled=false
syncLimit=2
initLimit=5
tickTime=2000
server.1=localhost:2721:2731:participant;localhost:2791
server.2=localhost:2722:2732:participant;localhost:2792

server 2:
dataDir=/home/shralex/zk-sat/zookeeper2
standaloneEnabled=false
syncLimit=2
initLimit=5
tickTime=2000
server.2=localhost:2722:2732:participant;localhost:2792

starting server 2 first. it says its the leader. starting server 1. then
connecting to server 2 with a client and issuing a reconfig adding server 1

Alex


On Fri, Jun 19, 2015 at 6:27 PM, Benjamin Anderson <b@banjiewen.net> wrote:

> Hi there - I'm working on automating bootstrapping of a 3-node ZK
> 3.5.0-alpha ensemble and I'm running in to some problems with getting
> the nodes to join up. The dynamic configuration page[1] suggests that,
>
> "...it is possible to start a ZooKeeper ensemble containing a single
> participant and to dynamically grow it by adding more servers"
>
> which is what I'm attempting to do. I've found, however, that this can
> be rather problematic. What is the "correct" procedure for dynamically
> growing an ensemble from a single participant?
>
> I've tried two approaches:
>
> Approach A:
>
> 1. Start two nodes, one with myid=1 and one with myid=2. Each node's
> dynamicConfigFile contains a single line referring to itself, i.e.,
> neither node is aware of the other.
>
> 2. Open a zkCli to either of the two nodes and issue a `reconfig`
> command to add the other, unknown node.
>
> This method fails with "KeeperErrorCode = NewConfigNoQuorum for".
>
> Approach B:
>
> 1. Start one node with myid=1 and a dynamicConfigFile that only refers
> to itself, then start a second node with myid=2 and a
> dynamicConfigFile that refers to itself *and* the node with myid=1.
>
> 2. Open a zkCli to the node with myid=1 and issue a reconfig command
> to add the node with myid=2.
>
> This approach works! However, if the ordering is reversed (i.e., the
> myid=2 node boots first and refers only to itself, and the myid=1 node
> refers to both itself and the myid=2 node,) then the myid=1 node will
> *never* come up cleanly - it hangs forever logging messages such as
> the one in this gist[2]. In my environment the boot ordering is not
> guaranteed, so this is rather challenging for me.
>
> My baseline config is roughly this[3].
>
> Is there a well-known and reliable way to incrementally join nodes to
> a ZK ensemble in 3.5.0-alpha? Do I need to be using a newer version
> than the release cut back in August 2014?
>
> Thanks!
> --
> b
>
> [1]: http://zookeeper.apache.org/doc/trunk/zookeeperReconfig.html
> [2]: https://gist.github.com/banjiewen/936f5620d33a8eb0ddf4
> [3]: https://gist.github.com/banjiewen/c7f11c749933ac1bab72
>

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