Add URL rewriting in Rails

[hunchr]

TICKET-23056

Discussed with @sislr

[coorasse]

Why do we do this on the app layer and not cloudflare?

[hunchr]

Why do we do this on the app layer and not cloudflare?

I'd also prefer to configure it in Cloudflare tbh. But @sislr prefers it to be in the code rather than "hidden in Cloudflare"

@schmijos what's your opinion?

[sislr]

Suggested change

	if (app_host = ENV["APP_HOST"]).present?
	match "*path", constraints: ->(req) { req.host != app_host && !req.path.start_with?("/.well-known/") },
	to: redirect { |_params, req| "https://#{app_host}#{req.fullpath}" }, via: :all
	end
	if (canonical_host = ENV["CANONICAL_HOST"]).present?
	match "*path", constraints: ->(req) { req.host != canonical_host && !req.path.start_with?("/.well-known/") },
	to: redirect { |_params, req| "https://#{canonical_host}#{req.fullpath}" }, via: :all
	end

I'd rather use a separate ENV variable here. APP_HOST is in most cases also set in staging apps AFAIK

[hunchr]

Isn't that what we want? If the env is set in staging/develop, then the deplo.io host redirects to renuoapp.

[schmijos]

I prefer to have this things in code as well if feasible.
The default should not be that we have proxy page rules in Cloudflare.
They are comfortable and fast to set up. But they are confusing to reason about. And we don't test them.

Consider the example here: https://renuo.slack.com/archives/C18D5LVDF/p1768293590120929

In order that a page rule works, you must have at least a record on that domain you want to be effected

Cloudflare needs a domain to point to somewhere for it to be proxyable.
So we end up with defunct DNS records.
In my understanding of the world DNS should come first.
Only after, a proxy should do the rewriting. Cloudflare inversed this:

1. First it will answer with a Cloudflare IP
2. Then it will apply the page rules
3. And only afterwards it will look at your DNS records.

It seems that DNS is not powerful enough for what people want to do.
And I think it's fine to use Cloudflare as a proxy. But we're mixing things up.

[hunchr]

Okay, should we merge it then? This PR received three comments, but no approvals or requested changes.

[coorasse]

I still think this causes unnecessary load on our app. it should rather be on ngnix, but having the app responsible of jiggling with the domains still does not seem right to me: the app should not really care about the domains it responds to.