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nuke defunct in-practice section

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Adam Wiggins
2011-11-17 13:35:30 -08:00
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content/config-in-practice.md
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## Example: Canonical host config
[`rack-canonical-host`](https://github.com/tylerhunt/rack-canonical-host) is of Rack middleware for Ruby web apps which redirects the user to the canonical hostname for the app. For example, if your production deploy can be reached at both hostnames `www.example.com` and `example.com`, but you wish for `www.example.com` to be the canonical host, using `rack-canonical-host` will automatically redirect users there when they access it on `example.com`.
## Doing it wrong #1: Hostname as a constant in the code
CANONICAL_HOST = 'www.example.com'
use(Rack::CanonicalHost, CANONICAL_HOST)
This violates twelve-factor because it stores config in the codebase.
## Doing it wrong #2: Hostname from conditional on "environment"
use Rack::CanonicalHost do
case ENV['RACK_ENV'].to_sym
when :staging then 'example.com'
when :production then 'staging.example.com'
end
end
This violates twelve-factor because it uses a conditional on the `RACK_ENV` value which stores an deploy name like `staging` or `production`. This stores config in the codebase (the hardcoded hostnames), and uses a non-granular, non-orthogonal deploy name to choose the canonical host. Both of these things make it impossible to add new deploys without changing the code. (As a thought experiment, imagine what it would take to open-source an app that had the above block of code in it.)
## Doing it right: Hostname from an env var
use(Rack::CanonicalHost, ENV['CANONICAL_HOST']) if ENV['CANONICAL_HOST']
## Doing it really right: Library uses env var directly
A well-written library of the nature of `rack-canonical-host` will use the enviroment variable directly, simplifying the code even further:
use Rack::CanonicalHost