Bug replicating app

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The issue this app is replicating is FIXED as of the 18/11/2020.
This repo only will stay up as documentation since it is linked across the issues mentioned below.

The fix:

Update Bundler, as it's where the fix has been implemented.

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The setup:

bundle install The app has been tested with Ruby 2.6.5 and Ruby 2.7.0. (To try it with Ruby 2.7.0 switch to branch ruby-2.7.0)

The test:

Running bin/foreman start karafka or bundle exec foreman start karafka

What should happen:

The Karafka server should display the initial config, then (in absence of an actual Karafka::App.boot! instruction) stop with a 0 exit-code.

karafka.1 | started with pid 70789
karafka.1 | Karafka version: 1.3.1
karafka.1 | Ruby version: 2.6.5
karafka.1 | Ruby-kafka version: 0.7.10
karafka.1 | Application client id:
karafka.1 | Backend: inline
karafka.1 | Batch fetching: true
karafka.1 | Batch consuming: false
karafka.1 | Boot file: /Users/aquaj/Code/external/broken-zeitwerk-minimal-ex/karafka.rb
karafka.1 | Environment: development
karafka.1 | Kafka seed brokers: ["kafka://127.0.0.1:9092"]
karafka.1 | exited with code 0

What happens: (the issue)

karafka.1 | bundler: failed to load command: karafka (/Users/aquaj/.rbenv/versions/2.6.5/bin/karafka)
karafka.1 | LoadError: cannot load such file -- /Users/aquaj/Code/external/broken-zeitwerk-minimal-ex/app/channels/application_cable

What we know about the issue

It does not happen without Zeitwerk

Switching to a config.autoloader = :classic in config/application.rb is enough to fix the issue.

It happens when Karakfa requires config/environment.rb

Removing the require in ./karafka.rb is enough for it to work. It's notable that this line is part of the official Karafka documentation on how to integrate with Rails.

It appears to be related to Bundler's Rubygems reset

Both Rubygems, Zeitwerk and Bundler override Kernel's require method. Rubygem's override is reset by Bundler during its setup. Normally this is no issue and works great but in our case, for reasons yet unknown, Bundler's reset comes after Zeitwerk's instead of its usual after, returning Kernel#require to its pre-Zeitwerk implementation, and breaking Zeitwerk behaviour.

It doesn't happen if you don't use Foreman

bundle exec karafka server works great.

It doesn't happen if it's not Karafka running the boot file

If the Procfile states karafka: bundle exec ruby karafka.rb instead of karafka: bundle exec karafka server, the issue seems to disappear.

It doesn't happen if you use a karafka binstub instead

If the Procfile states karafka: bin/karafka server instead of karafka: bundle exec karafka server, the issue seems to disappear. It does happen whether you use a foreman binstub or not though.

The open issues related to this app:

• fxn/zeitwerk#104
• https://github.com/bundler/bundler/issues/7553