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From Eric Yang <eric...@gmail.com>
Subject Re: Hadoop Master and Slave Discovery
Date Tue, 05 Jul 2011 22:00:14 GMT
In another project, I have implemented a bonjour beacon (jmdns) which
sit on the Zookeeper nodes to advertise the location of zookeeper
servers.  When clients start up, it will discover location of
zookeeper through multicast dns.  Once, the server locations are
resolved (ip:port and TXT records), the clients shutdown mdns
resolvers.  Client proceed to use the resolved list for zookeeper
access.  There does not seem to be cpu overhead incurred by the
beacon, nor the clients.  If a client could not connect to zookeeper
anymore, then it will start mdns resolvers to look for new list of
zookeeper servers.  The code for the project is located at:


It may be possible to use similar approach for location resolution,
and load rest of the config through zookeeper.


On Tue, Jul 5, 2011 at 2:40 AM, Steve Loughran <stevel@apache.org> wrote:
> On 04/07/11 18:22, Ted Dunning wrote:
>> One reasonable suggestion that I have heard recently was to do like Google
>> does and put a DNS front end onto Zookeeper.  Machines would need to have
>> DNS set up properly and a requests for a special ZK based domain would
>> have
>> to be delegated to the fancy DNS setup, but this would allow all kinds of
>> host targeted configuration settings to be moved by a very standardized
>> network protocol.  There are difficulties moving port numbers and all you
>> really get are hostnames, but it is a nice trick since configuration of
>> which nameserver to use is a common admin task.
> good point
> 1. you could use DNS proper, by way of Bonjour/avahi. You don't need to be
> running any mDNS server to support .local, and I would strongly advise
> against it in a large cluster (because .local resolution puts a lot of CPU
> load on every server in the subnet). What you can do is have the DNS server
> register some .local entries and have the clients use this to bind. You
> probably also need to set the dns TTLs in the JVM. In a large clusters
> that'll just add to the DNS traffic, so it's where host tables start to look
> appealing
> 2. Apache MINA is set up to serve its directory data in lots of ways,
> including what appears to be text files over NFS. This is an even nicer
> trick. If you could get MINA to serve up the ZK data, life is very simple
>> On Mon, Jul 4, 2011 at 3:44 AM, Steve Loughran<stevel@apache.org>  wrote:
>>> On 03/07/11 03:11, Raja Nagendra Kumar wrote:
>>>> Hi,
>>>> Instead of depending on local syncup to configuration files, would it be
>>>> a
>>>> nice way to adopt JINI Discovery model, where in masters and slaves can
>>>> discover each other dynamically through a UDP broadcast/heart beat
>>>> methods
>>> That assumes that UDP Broadcast is supported through the switches (many
>>> turn it off as it creates too much traffic), or UDP multicast is
>>> supported
>>> (as an example of an infrastructure that does not, play with EC2)
>>>  This would mean, any machine can come up and say I am a slave and
>>>> automatically discover the master and start supporting the master with
>>>> in<
>>>> x seconds.
>>> How will your slave determine that the master that it has bonded to is
>>> the
>>> master that it should bond to and not something malicious within the same
>>> multicast range? It's possible, but you have generally have to have
>>> configuration files in the worker nodes.
>>> There's nothing to stop your Configuration Management layer using
>>> discovery
>>> or central config servers (Zookeeper, Anubis, LDAP, DNS, ...), which then
>>> pushes desired state information to the client nodes. These can deal with
>>> auth and may support infrastructures that don't support broadcast or
>>> multicast. Such tooling also gives you the ability to push out host table
>>> config, JVM options, logging parameters, and bounce worker nodes into new
>>> states without waiting for them to timeout and try to rediscover new
>>> masters.

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