Detect if the middleware is already loaded and prevent it from being loaded twice

We're running a Rails 6 app on Heroku with rack-timeout initialized with: config.middleware.use Rack::Timeout, service_timeout: 25, wait_timeout: 25

The errors we see in our exception tracking look legit, eg:
Rack::Timeout::RequestTimeoutError (Request waited 6ms, then ran for longer than 24994ms )

However what actually happens is that the requests timeout after pretty much exactly 15 seconds every time.

From the browsers point of view:

From the logs:
08 Dec 2020 09:26:40.810256 <190>1 2020-12-08T08:26:40.4593+00:00 app web.1 - - E, [2020-12-08T08:26:40.459200 #153] ERROR -- : source=rack-timeout id=e14e9348-e767-4b66-82aa-8c32821a0b3b wait=6ms timeout=24994ms service=15000ms state=timed_out

(note that we have timeout=24994ms but service=15000ms)

What's going on here?

Start by inspecting the Rails middleware configuration and rack-timeout initialization described in the issue, then check the middleware stack for duplicate rack-timeout entries. Reproduce the reported 25-second timeout configuration and compare the configured service timeout with the observed 15-second value. Done means duplicate loading is detected or prevented and the timeout behavior is consistent.