Add node to cluster command

[ppikula]

I've introduced new commands to mongooseimctl - add_to_cluster and remove_from_cluster that simplify clustering procedure. Moreover I've added add_table_copy to all mnesia modules, it is useful when configuration changes and new modules with mnesia tables are added, then it will create replicas.

Is the add_table_copy going to break anything, should all the tables have replicas on each node?
Maybe it is a good idea to make it configurable?

[michalwski]

I would print the $MNESIA_DIR in this message also just to make it more clear what to remove.

[michalwski]

Is the add_table_copy going to break anything, should all the tables have replicas on each node?

No, this shouldn't break anything. It will just force replicating given table on the current node as you noticed.

Maybe it is a good idea to make it configurable?

Yes, that's a good idea. I think every module creating the mnesia table should have parameter:

{local_replicas, [{TableName Type}]}

Where TableName is the mnesia table name (usually there is one table per module but some modules requires more tables). Type is either ram_copies, disc_copies, disc_only_copies or none. The last one means that given node will not have replica for given table. If not specified the behaviour should be like it is now, in this pull request I mean.

[michalwski]

any chance to finish this?

[mongoose-im]

travis is using test branch add_node_to_cluster_command from https://github.com/esl/ejabberd_tests/tree/add_node_to_cluster_command