[ejabberd] Node Clustering issue

Florian Jensen admin at flosoft.biz
Thu Jun 12 12:34:07 MSD 2008


thanks a million for the detailed commands.

For 1: I installed erlang-nox.

I got my nodes setup to copy. I can see the node connected in the 
web-admin panel, when I am using the console command. But when I then 
start ejabberd, it doesn't connect to the node.
ds2581 only sees himself.
ds2248 sees the second node as stopped.

What am I missing?


Florian Jensen

Matthew Reilly wrote:
> Florian Jensen wrote:
>> Ok, I got it running. I now can access the erlang console.
> Out of curiosity, how did you get it fixed?
>> So, now, how can I let it sync all? And how can I let it start
>> automatically in cluster mode?
> I'm doing this from memory, so I apologize if I get something wrong.
> Now that you have connected, you should be able to do (from the erlang
> console):
> erl>  mnesia:info().
> This should show both your main node and your new node.
> You want to have it set up so that the next time you start your new
> node, it remembers to connect to the original node.
> To do this:
> erl>  mnesia:change_table_copy_type(schema,node(),disc_copies).
> This creates a copy of the mnesia schema on the local drive, so that
> when you restart the local node, it remebers to connect to the main node.
> What that means is that when you kill your console (with
> control-C/control-C), and start ejabberd on the second node (with the
> same ./start script), it will come up in clustered mode -- you don't
> need to do anything else for (basic) clustering! (on the ejabberd side
> -- you still need to set up DNS entries pointing to the second node, or
> no clients will find it).
> Once you've done this, the first node stores all data, and the second
> node stores none of the data (except for the schema itself). This means
> that every mnesia lookup (which is done e.g. everytime a
> message/presence stanza is sent) works by having the second node send a
> network request to the first node, the first node lookups up the info in
> its mnesia table and sends it back to the second node.
> That is the default behavior, which may be acceptable --the mnesia
> traffic/CPU load is not very large. However, this only gives you
> scalability benefits of clustering, but not fault-tolerance. For
> example, if your first node went down, the second node would suddenly
> become unusable (since it has no copies of the mnesia tables locally).
> To add fault tolerance, you'll need to stay in the console mode (or
> reenter it if you've left it), and do a mnesia:add_table_copy() for each
> table. This'll be tedious, and if anyone else knows a more automated
> way, I'd like to hear it.
> To get a list of the tables, do:
> erl>  mnesia:info().
> You get output similar to:
> [{'ejabberd at ds2248',ram_copies}] = [session,route, ...]
> [{'ejabberd at ds2248',disc_copies}] = [privacy,...]
> [{'ejabberd at ds2248',disc_only_copies}] = [offline_msg,...]
> There are three types of tables: RAM resident (ram_copies), RAM&  disc
> resident (disc_copies), and just disc resident (disc_only_copies).
> For each table, you tell the mnesia system that you want a clustered
> copy on the second node by issuing these commands from the erlang
> console (one the second node):
> erl>  mnesia:add_table_copy(session,node(),ram_copies).
> erl>  mnesia:add_table_copy(route,node(),ram_copies).
> ...
> mnesia:add_table_copy(privacy,node(),disc_copies).
> ...
> erl>  mnesia:add_table_copy(offline_msg,node(),disc_only_copies).
> ...
> If you do this for each table, the second node will be able to keep
> running if the first dies. You only have to do this once -- even if you
> restart the second node, it knows which tables to cluster.
> Note: The actual list of tables you'll need to cluster will differ
> depending on the modules you've configured in your ejabberd.cfg as well
> as whether you're using a SQL backend. If you add a new module to
> ejabberd.cfg, it may add a new mnesia table, and you made need to do a
> mnesia:add_table_copy() for the new table.
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