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From Edward Capriolo <edlinuxg...@gmail.com>
Subject Re: Initialising / maintaining a list of nodes in the cluster
Date Sun, 08 Sep 2013 02:04:47 GMT
A cassandra cluster must always use the same rpc port default 9160

On Friday, September 6, 2013, Paul LeoNerd <leonerd@leonerd.org.uk> wrote:
> I'm trying to work out how a client is best to maintain a list of what
> nodes are available in the cluster, for maintaining connections to.
>
> I understand the general idea is to query the "system.peers" table, and
> REGISTER an interest in TOPOLOGY_CHANGE and STATUS_CHANGE messages to
> watch for nodes being added/removed or becoming unavailable/available.
> So far so good.
>
> A few details of this seem a bit awkward though:
>
>  * The "system.peers" table identifies peers only by their IP address,
>    not including the port number, whereas TOPOLOGY and STATUS_CHANGE
>    messages include a port.
>
>    What happens if there is more than one copy of a node using the same
>    IP address? How do I know which TCP port I can use to communicate
>    CQL with a given peer?
>
>  * The "system.peers" table doesn't contain any information giving the
>    current availability status of the nodes, so I don't know if they
>    are initially up or down.
>
>    I can just presume all the known nodes are up until I try connecting
>    to them - in any case, it could be that Cassandra knows of the
>    existence of nodes that for some reason my client can't connect to,
>    so I'd have to handle this case anyway. But it feels like that hint
>    should be there somewhere.
>
>  * The "system.peers" table doesn't include the actual node I am
>    querying it on.
>
>    Most of the missing information does appear in the "system.local"
>    table, but not the address. The client does know /an/ address it has
>    connected to that node using, but how can I be sure that this
>    address is the one that will appear in the "peers" list on other
>    nodes? It's quite common for a server to have multiple addresses, so
>    it may be that I've connected to some address different to that
>    which the other nodes know it by.
>
> I'm quite new to Cassandra, so there stands a chance I've overlooked
> something somewhere. Can anyone offer any comment or advice on these
> issues, or perhaps point me in the direction of some client code that
> manages to overcome them?
>
> Thanks,
>
> --
> Paul "LeoNerd" Evans
>
> leonerd@leonerd.org.uk
> ICQ# 4135350       |  Registered Linux# 179460
> http://www.leonerd.org.uk/
>

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