[ejabberd] Clustering question...

rana das ranaraj1983 at gmail.com
Tue May 8 21:58:59 MSK 2012

unsubcribe me pls

On Tue, May 8, 2012 at 11:24 PM, Felix GV <felix at mate1inc.com> wrote:

> Hmm... ok thanks :)
> --
> Felix
> On Tue, May 8, 2012 at 2:55 AM, Michael Weibel <michael.weibel at gmail.com>wrote:
>> Hi Felix,
>> First, full disclosure: The project I'm working on and which will
>> massively use ejabberd is not live yet, so I'm not production proven yet.
>> > It does seem to work when I take off the extra_db_nodes parameter from
>> the start up script. So that parameter is just for setting up replication,
>> you say? Interesting...!
>> >
>> > However, the official guide and the one I linked to mention to add this
>> parameter to the second (or extra) node only. In my case, it seems the
>> clustering was not proper until I also added the parameter to the
>> first/original node. But you are right that once the clustering is set up,
>> then it seems possible to take off that parameter and things still work
>> (with the expected fault-tolerance and all)...!
>> >
>> > In your experiments, did you (initially) add that parameter to all
>> nodes, or were you able to get things working correctly by adding it to the
>> second node only? I'm wondering if I'm coming to the right conclusions, or
>> if something else is going on in my environment that would have caused the
>> behavior I observed...!
>> Basicly as we setup the clustering in our test environment we did it more
>> or less this way:
>> - Modify ejabberdctl.cfg to have the correct ERLANG_NODE setting (both
>> nodes)
>> - Copy .ejabberd.cookie from first node to second node
>> - Stop ejabberd on first node
>> - erl -sname SECOND_ERLANG_NODE -mnesia extra_db_nodes
>> "['FIRST_ERLANG_NODE']" -mnesia dir '"var/lib/ejabberd/"'
>> - mnesia:change_table_copy_type(schema, node(), disc_copies).
>> - q().
>> - start ejabberd on first node again
>> - go to webinterface of first node and you should see the second node
>> - go to webinterface of second node and change all mnesia table copy
>> types to match the ones from first node (you can do that from the cli as
>> well but on the webinterface it's much easier to do for only a few nodes)
>> This should work without specifying extra_db_nodes at all after the first
>> setup.
>> Basicly I have been told that clustering in erlang is done solely by
>> replicating the mnesia tables. Everything else works out of the box due to
>> built-in clustering in erlang.
>> > Regarding your other comment: I am surprised that you say the
>> configuration of Mnesia should be the same on both/all nodes, because that
>> would imply that Remote copies are never ok. Is that what you mean?
>> I'm not yet at the point to say that for sure. But anyway if you need to
>> scale, you should use mnesia as less as possible (better use
>> PostgreSQL/MySQL)..
>> >
>> > I'm definitely looking forward to reading your blog posts on the
>> subject! Do post them here once you write them, please :) !
>> Of course I will do that :)
>> - Michael
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Rana Das

Software Engineer
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