[BUG]: undefined method 'subdomain' for an instance of Rack::Request (NoMethodError) #4784
Description
Tracer Version(s)
2.18.0
Ruby Version(s)
ruby 3.4.3 (2025-04-14 revision d0b7e5b6a0) +PRISM
Relevent Library and Version(s)
No response
Bug Report
In the past few days, we've had spikes of error requests in our application. Requests from bots (including DD Synthetics) are triggering trace errors on innocuous routes (/favicon, /wp-admin/).
nomethoderror: undefined method 'subdomain' for an instance of Rack::Request
/usr/local/bundle/ruby/3.4.0/gems/actionpack-8.0.2/lib/action_dispatch/journey/route.rb:153:in 'block in ActionDispatch::Journey::Route#matches?': undefined method 'subdomain' for an instance of Rack::Request (NoMethodError)
from /usr/local/bundle/ruby/3.4.0/gems/actionpack-8.0.2/lib/action_dispatch/journey/route.rb:150:in 'Hash#each'
from /usr/local/bundle/ruby/3.4.0/gems/actionpack-8.0.2/lib/action_dispatch/journey/route.rb:150:in 'Enumerable#all?'
from /usr/local/bundle/ruby/3.4.0/gems/actionpack-8.0.2/lib/action_dispatch/journey/route.rb:150:in 'ActionDispatch::Journey::Route#matches?'
from /usr/local/bundle/ruby/3.4.0/gems/actionpack-8.0.2/lib/action_dispatch/journey/router.rb:121:in 'block in ActionDispatch::Journey::Router#find_routes'
from /usr/local/bundle/ruby/3.4.0/gems/actionpack-8.0.2/lib/action_dispatch/journey/router.rb:121:in 'Array#select!'
from /usr/local/bundle/ruby/3.4.0/gems/actionpack-8.0.2/lib/action_dispatch/journey/router.rb:121:in 'ActionDispatch::Journey::Router#find_routes'
from /usr/local/bundle/ruby/3.4.0/gems/datadog-2.18.0/lib/datadog/tracing/contrib/action_pack/action_dispatch/instrumentation.rb:67:in 'Datadog::Tracing::Contrib::ActionPack::ActionDispatch::Instrumentation::Journey::LazyRouter#find_routes'
from /usr/local/bundle/ruby/3.4.0/gems/actionpack-8.0.2/lib/action_dispatch/journey/router.rb:69:in 'ActionDispatch::Journey::Router#recognize'
from /usr/local/bundle/ruby/3.4.0/gems/datadog-2.18.0/lib/datadog/appsec/api_security/route_extractor.rb:50:in 'Datadog::AppSec::APISecurity::RouteExtractor.route_pattern'
from /usr/local/bundle/ruby/3.4.0/gems/datadog-2.18.0/lib/datadog/appsec/api_security/sampler.rb:47:in 'Datadog::AppSec::APISecurity::Sampler#sample?'
from /usr/local/bundle/ruby/3.4.0/gems/datadog-2.18.0/lib/datadog/appsec/api_security.rb:14:in 'Datadog::AppSec::APISecurity.sample?'
from /usr/local/bundle/ruby/3.4.0/gems/datadog-2.18.0/lib/datadog/appsec/contrib/rack/request_middleware.rb:119:in 'Datadog::AppSec::Contrib::Rack::RequestMiddleware#call'
from /usr/local/bundle/ruby/3.4.0/gems/datadog-2.18.0/lib/datadog/tracing/contrib/rack/middlewares.rb:70:in 'block in Datadog::Tracing::Contrib::Rack::TraceMiddleware#call'
from /usr/local/bundle/ruby/3.4.0/gems/datadog-2.18.0/lib/datadog/tracing/contrib/rack/trace_proxy_middleware.rb:17:in 'Datadog::Tracing::Contrib::Rack::TraceProxyMiddleware.call'
from /usr/local/bundle/ruby/3.4.0/gems/datadog-2.18.0/lib/datadog/tracing/contrib/rack/middlewares.rb:49:in 'Datadog::Tracing::Contrib::Rack::TraceMiddleware#call'
from /usr/local/bundle/ruby/3.4.0/gems/actionpack-8.0.2/lib/action_dispatch/middleware/static.rb:27:in 'ActionDispatch::Static#call'
from /usr/local/bundle/ruby/3.4.0/gems/railties-8.0.2/lib/rails/engine.rb:535:in 'Rails::Engine#call'
from /usr/local/bundle/ruby/3.4.0/gems/puma-6.6.0/lib/puma/configuration.rb:279:in 'Puma::Configuration::ConfigMiddleware#call'
from /usr/local/bundle/ruby/3.4.0/gems/puma-6.6.0/lib/puma/request.rb:99:in 'block in Puma::Request#handle_request'
from /usr/local/bundle/ruby/3.4.0/gems/puma-6.6.0/lib/puma/thread_pool.rb:390:in 'Puma::ThreadPool#with_force_shutdown'
from /usr/local/bundle/ruby/3.4.0/gems/puma-6.6.0/lib/puma/request.rb:98:in 'Puma::Request#handle_request'
from /usr/local/bundle/ruby/3.4.0/gems/puma-6.6.0/lib/puma/server.rb:472:in 'Puma::Server#process_client'
from /usr/local/bundle/ruby/3.4.0/gems/puma-6.6.0/lib/puma/server.rb:254:in 'block in Puma::Server#run'
from /usr/local/bundle/ruby/3.4.0/gems/puma-6.6.0/lib/puma/thread_pool.rb:167:in 'block in Puma::ThreadPool#spawn_thread'
I threw the stack track at Claude and Claude Code (both using Opus 4), both think Datadog would be a possible culprit:
Datadog APM integration issue: The stack trace shows Datadog's APISecurity module trying to extract route patterns. It may be passing a raw Rack::Request instead of the expected ActionDispatch::Request to Rails' route matching logic.
I don't necessarily take that at face value, but our update of the gem (from 2.17.0 to 2.18.0) got deployed this morning, and this is when the errors started. Since that version also introduces Datadog::AppSec::APISecurity::RouteExtractor, it's not impossible the two are related.
Reproduction Code
No response
Configuration Block
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Error Logs
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Operating System
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How does Datadog help you?
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