Managing configuration in Erlang application

Question

I need to distribute some sort of static configuration through my application. What is the best practice to do that?

I see three options:

1. Call ap

Answer 1

You could use a process (a gen_server maybe?) to store your configuration parameters in its state. It should expose a get/set interface. If a value hasn't been explicitly set, it should retrieve a default value.

-export([get/1, set/2]).

...

get(Param) ->
  gen_server:call(?MODULE, {get, Param}).

...

handle_call({get, Param}, _From, State) ->
  case lookup(Param, State#state.params) of
    undefined ->
      application:get_env(...);
    Value ->
      {ok, Value}
  end.

...

You could then easily mockup this module in your tests. It will also be easy to update the process with some new configuration at run-time.

You could use pattern matching and tuples to associate different configuration parameters to different modules:

set({ModuleName, ParamName}, Value) ->
  ...

get({ModuleName, ParamName}) ->
  ...

Put the process under a supervision tree, so it's started before all the other processes which are going to need the configuration.

Oh, I'm glad nobody suggested parametrized modules so far :)