Don't fallback to RACK_ENV when RAILS_ENV is not present

[dmathieu]

RACK_ENV is not the same as RAILS_ENV, and can't serve as a fallback when the later isn't present.

See http://www.hezmatt.org/~mpalmer/blog/2013/10/13/rack_env-its-not-for-you.html

In fact, it can even cause some issues if your app is using unicorn, as they're including internal rack middlewares relying on RACK_ENV to have the deployment value.
See https://github.com/defunkt/unicorn/blob/master/lib/unicorn.rb#L56-L79

Rack itself does that too.
https://github.com/rack/rack/blob/4e4ab39b0508aa3e59f5d7e53696ef6ae7c220ed/lib/rack/server.rb#L228

This removes support for falling back to RACK_ENV when RAILS_ENV is not available.

[arthurnn]

Good catch. So this is only working right now, because for development RACK_ENV and RAILS_ENV are, coincidentally the same. And on production, RAILS_ENV is always set to production value.
👍 from me, @jeremy @tenderlove @spastorino what do you guys think?

[tenderlove]

Agree with @dmathieu. It's not a valid fallback option.

[arthurnn]

@dmathieu can you add a Changelog entry for that?
thanks btw!

[dmathieu]

@arthurnn: sure, will do.

[spastorino]

Agreed 👍, maybe for another PR we should investigate a better way to integrate both things.

[jeremy]

Considering this was intentionally, thoroughly, and publicly supported, we should go through a deprecation cycle to remove it.

[jeremy]

After looking into the history, 👎 entirely. RACK_ENV grew out of a Rack server convention that multiple servers supported, then Rack::Server included. The fact that Rack::Server happened to have these default middleware stacks doesn't imply that it's the only allowed values, the only intended values, or part of the SPEC 😁

There's a long history of using RACK_ENV to communicate exactly what it is: the environment you're running the Rack app in, not the Rack environment.

[dmathieu]

@jeremy do as you wish. I just want to mention that it makes IE very slow on some versions of AWS's ELB, which can be a big issue for anyone.
If you think this shouldn't be fixed in rails, there's something that should be changed in rack, because there is definitely a bug here.

[mathieujobin]

was there any consideration falling back to APP_ENV ?