How can I add setcookie into ejabberdctl to run the ejabberd service or connect two node on different machine without setcookie in startup?

Question

I am new the Erlang. Currently, we are using ejabberd for our xmpp service. Recently, dues to some capability issue, I have written a distributed erlange program. I need to run rpc:call between two machines. I can do the rpc:call successfully on erl simulator. But our current system was using ejabberdctl to start the ejabberd service. I have check and try to modify the ejabberdctl file. But I can't add -setcookie successfully.

the code section in ejabberdctl is

ctlexec()
{ 
    CONN_NAME=$1; shift
    COMMAND=$@
    $EXEC_CMD "$ERL \
    $NAME ${CONN_NAME} \
    -noinput \
    -hidden \
    -pa $EJABBERD_EBIN_PATH \
    $KERNEL_OPTS \
    -s ejabberd_ctl -extra $ERLANG_NODE $COMMAND"
}

the problem caused by the last two line:

  $KERNEL_OPTS \
  -s ejabberd_ctl -extra $ERLANG_NODE $COMMAND"

I think this file is referenced some one's before, but I don't know where are there from. Does anybody know how can I add -setcookie abc to this erl command? If I can't change the ejabberdctl file or the worse case, I can't change the current system. i.e. I don't have a chance to add setcookie to the ejabberd system. How can I connect my new node to the existing ejabberd node(our current system).

The ejabberd suppose to start first.

Answer 1

You have a solution right under your nose. How ctlexec() works? It runs --hidden node named $NAME ${CONN_NAME}, sets options $KERNEL_OPTS, inserts $EJABBERD_EBIN_PATH into search path and calls ejabberd_ctl:start() with some additional parameters in $ERLANG_NODE $COMMAND. So there must be -setcookie Cookie parameter in $KERNEL_OPTS or it uses default cookie in $HOME/.erlang.cookie. It is exactly what you need. Just replace -s ejabberd_ctl with your own module and use $KERNEL_OPTS and $ERLANG_NODE content which you already have. Search around in the script for clues what $KERNEL_OPTS and $ERLANG_NODE contains.

It is a usual way how scripts like ejabberd_ctl are made. It is pretty simple and elegant. You just run your own node set it --hidden so you don't disturb other nodes in a cluster if there is such. Don't forget set some random node name. Connect to the application node and then do your rpc:call/4,5 and that's it. There is usually some modules like ejabberd_ctl.erl to make it more comfortable, process extra parameters and so on.