[erlang-questions] Environment variables for release

AD <>
Wed Jan 9 15:12:57 CET 2013


Yea i think that was it thanks.  One follow-up here, the 'startup' of the
library depends on the parent app thats including it since it can override
some startup parameters via environment variables.  Is there a best
practice here?  I figure you can either

1 - manually start it with application:start(library) in the parent apps
start() and remove it from the auto-start list in release
2 - have a separate supervisor that starts the library but doesnt start the
workers (kind of like how cowboy only starts the clock, but you have to do
cowboy:start_http() in your app).

The problem is I only really have 1 gen_server to start and i would like
the calling application to load first so it can override with its own
environment vars.

Any best practice advise appreciated.

-A


On Mon, Jan 7, 2013 at 10:36 AM, Ulf Wiger <> wrote:

>
> One suggestion:
>
> The application lib must be loaded before get_env() can work.
>
> BR,
> Ulf W
>
> On 7 Jan 2013, at 15:15, AD wrote:
>
> Hello,
>
>  I have a library being built that is leveraging environment variables.
>  There is a line in the library include file that looks like
>
> -define(CONST, lib:get_env(Key,Default)).
>
> the lib:get_env function simply checks
>
>     application:get_env(lib, Key) % in order to check the library.app first
>  and then
>    application:get_env(Key) % check for local overrides
>
>  However when i place variables like the following in the main example.app
> file in ebin/
>
> {application,example,
>              [{description,[]},
>               {env,[{'COWBOY_HTTP_PORT',9090}]},
>               ......
>
> Nothing is getting read.  I am not sure if this needs to be in
> rel/files/app.config instead?
>
> Appreciate any help here.
>
> -AD
>
>
> _______________________________________________
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> 
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>
>
> Ulf Wiger, Co-founder & Developer Advocate, Feuerlabs Inc.
> http://feuerlabs.com
>
>
>
>
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