[erlang-questions] distributed system: same app, different params

Ulf Wiger <>
Thu Jun 18 09:10:03 CEST 2009


Roberto Ostinelli wrote:
> 
> what i do now is:
> 
> 1. i have an escript file which:
>     - reads the parameters from a configuration file
>     - starts the 2 erlang nodes, using os:cmd/1 and passing the 
> configuration parameters, with a command like
> 
> run_erl -daemon  $PIPE_DIR/$node_id $LOGS_DIR "exec erl -name $node_id 
> -run go start -params $params"
> 
> 2. in the module go, the function start/1:
>     - reads the passed parameters;
>     - starts the application my_app, passing the appropriate values.
> 
> 3. the escript file is started as daemon on the target machine.
> 
> 
> though this does work, it seems way too non-erlangish to me.

No, this is pretty much how it's done.

You could go even more non-erlangish and use normal environment
variables (which you can read from within Erlang using os:getenv(Var),
but the way you're doing it has the distinct advantage that it works
well even if the two nodes execute on the same machine.

What many applications (e.g. mnesia) use are OTP application environment
variables. You Erlang application can access them using

application:get_env(Var)   % the current application
application:get_env(App, Var)  % a specific application

An example of this would be erl ... -mnesia dir Path

BR,
Ulf W
-- 
Ulf Wiger
CTO, Erlang Training & Consulting Ltd
http://www.erlang-consulting.com


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