ruby 36 lines · 7 steps

Per-request context with CurrentAttributes in Rails

A Rack middleware, a Current model, and tagged logging combine to attach a request ID to every log line and make it globally reachable.

Explained by highlit

Rails Intermediate middleware thread-safety logging request-context rack

1module RequestTagging
2  class Middleware
3    def initialize(app)
4      @app = app
5    end
6 
7    def call(env)
8      request_id = env["action_dispatch.request_id"]
9      Current.request_id = request_id
10      @app.call(env)
11    ensure
12      Current.reset
13    end
14  end
15end
16 
17class Current < ActiveSupport::CurrentAttributes
18  attribute :request_id
19end
20 
21Rails.application.configure do
22  config.log_tags = [
23    :request_id,
24    ->(req) { "ip=#{req.remote_ip}" },
25    ->(req) { "method=#{req.request_method}" }
26  ]
27 
28  config.logger = ActiveSupport::TaggedLogging.new(
29    ActiveSupport::Logger.new($stdout)
30  )
31 
32  config.middleware.insert_after(
33    ActionDispatch::RequestId,
34    RequestTagging::Middleware
35  )
36end

01 / 01

STEP 01

Walkthrough

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Three takeaways

1CurrentAttributes gives you request-scoped global state that stays isolated across concurrent requests.
2Wrapping mutable per-request state in an ensure block guarantees cleanup even when the request raises.
3Tagged logging plus a shared request ID lets you trace every log line back to a single request.

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