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From Ramzi Rabah <rra...@playdom.com>
Subject Re: Connecting to the cluster with failover (was: data modeling question)
Date Mon, 07 Dec 2009 17:59:05 GMT
                TSocket socket = new TSocket(hostName, port);
                TBinaryProtocol binaryProtocol = new
TBinaryProtocol(socket, false, false);
                Cassandra.Client client = new Cassandra.Client(binaryProtocol);
                socket.open();
                Map<String,String> tokenToHostMap = (Map<String,String>)
                        new
JSONTokener(client.get_string_property(CassandraServer.TOKEN_MAP)).nextValue();

this will return a list of servers in the cluster (both up or down).

You will obviously need to connect to a live node in the cluster to be
able to run this.


On Mon, Dec 7, 2009 at 6:31 AM, Mark Robson <markxr@gmail.com> wrote:
>
>
> 2009/12/3 Coe, Robin <robin.coe@bluecoat.com>
>>
>> So, considering that I currently have to take down a node to make a CF
>> change, I'm wondering how to perform automatic failover from my application?
>>  Is there a mechanism by which I can request from Cassandra all the
>> destination IP:ports for the nodes in a cluster, so I can adapt dynamically?
>>  For example, if I ramp up/down Cassandra instances based on server load, I
>> would like my application to automatically know what servers are available,
>> to execute automatic reconnection when the node I'm connected to goes down.
>
> This is a bigger question and one which would merit some dicussion
> generally.
>
> Nodes will need to be taken down, not just for CF changes but any other
> operational reason, during which time you won't want to have an outage.
>
> Applications querying data will need to still be able to do it, and those
> inserting will also need to be able to continue to insert (or handle a
> backlog if that is acceptable to the end-users).
>
> My suggestions are:
>
> 1. Use a IP-layer load balancer like LVS and have the servers add/remove
> themselves from the pool as they are up/down
> 2. have all your app servers also be a Cassandra node, and always connect
> locally. If the local Cassandra instance is unhealthy, remove the whole app
> server from the LVS pool.
>
> Of course you don't need to use LVS, any other IP-based load balancer would
> do. And of course, Cassandra itself needs a fixed non-changing address per
> node, so it would need to make sure it didn't use that address.
>
> In the event of a normal (i.e. administrative) shutdown, the admin could
> manually set the node down before doing the maintenance.
>
> I did some work on an experimental load balancer I call "Fluffy Cluster"
> here:
>
> http://code.google.com/p/fluffy-linux-cluster/
>
> This is not production-ready yet but could be useful.
>
> Mark
>

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