Disabling Flipper preload entirely for a given Rails controller

[jeffbax]

I came across this previous issue trying to find a solution where I could avoid Flipper preloading on certain controllers entirely… alas I couldn't seem to find a middleware to insert before/after that would have request.env['action_dispatch.request.path_parameters'][:controller] populated for inspection within the preload proc.

Basically the use case is that about 50% of our traffic hits the Rails app but is proxying Webflow pages, where there is no flipper usage at all, but there is unfortunately not a reliable path or subdomain that is used only for our actual application that I could easily target like the examples.

All of the proxying goes through the same controller, so ideally I could just disable preload in that context, but I've not been able to find that solution yet (and mucking around too much with the middleware has me concerned with long term brittleness).

Has anyone had to do something similar, or know of something I'm missing?

[jnunemaker]

Is there a known route path prefix or something for that controller? You can just configure preload like this: config.flipper.preload = -> (request) { !request.path.start_with?('/assets') }

[jeffbax]

No, there is not a reliable path or subdomain that I can use to target the path alone, thus my conundrum trying to find an alternative 🥲

[jnunemaker]

What does your route look like? Maybe I can backtrack something from that

…

On Tue, Sep 23, 2025 at 4:19 PM Jeff Baxendale ***@***.***> wrote: No, there is not a reliable path or subdomain that I can use to target the path alone, thus my conundrum trying to find an alternative 🥲 — Reply to this email directly, view it on GitHub <#941 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAAAB23HJSVISP76YTTOOIL3UGTL7AVCNFSM6AAAAACHJOPVQGVHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTINBZGA2TINY> . You are receiving this because you commented.Message ID: ***@***.***>

[jeffbax]

Not sure I am fully following what you mean by the route, but to describe things further basically our app has dozens to hundreds of paths from the root (for things like marketing and SEO) that all resolve to a single controller that proxies Webflow... so the vast majority of routes qualify for flipper exclusion, and grow kind of as marketing wants them to.

ex:

• /ux-research-career-guide-download
• /blog

So if I could just target that controller it would be the easiest lift as its the only one I really want to exclude, and its basically an infinite list of routes that can resolve to it.

Alternatively, I think I'm going to try to see if I can somehow read the RouteSet at config if it is available, and parse the paths from there. If not that, will probably maintain the a list by hand as it is probably easier to maintain the app route module namespaces (even if missing some at times) than deal with the rate at which marketing ones get added.

But either way ultimately leaves a cumbersome process of maintaining an ever growing approve/disapprove list that can always grow and be missed. It would be easier if our app ran on a subdomain or /app/ etc, but at the moment we aren't able to move to that.

[jnunemaker]

Sorry, I meant like what is in config/routes.rb to route to the controller. I thought maybe I could pull something from that to route via the request object. Worst case it is possible to route from the preload block based on the request and if its the controller then disable preloading but it would require duplicate route lookup.

[jeffbax]

We basically maintain an entire external-routes.rb that our marketing team updates to point the controller to new webflow proxy, so it kind of grows and grows and grows as they add new pages.

I think its your last part that I get a little lost on, are you saying attempt to parse Rails.application.routes.routes manually and build up a collection of paths at boot to pass into the preload filter?

Overall when just printing them all out, there is a set of modules that I can try to target, just that whitelisting things is harder to keep up with than if there were an ability to say "never these controllers," or if there was some kind of filter that could stamp to the class to avoid things. Although most of our new controllers are API controllers, so maybe it's good enough for now.

I was also trying to see if Flipper set a flag or something to indicate whether it was preloaded or not, which I could then wire up to a logger to spot things I missed but wasn't able to find something like that so far.

(sorry for delay, broke my elbow this weekend)