Sidekiq 7.3.x and connection_pool 3.0 - incompatibility that breaks workers

Feb 15, '26 20:03

1 min. read

This content has been automatically translated from Ukrainian.

Recently, while deploying a Rails application on Coolify, I encountered an error that is not immediately obvious. Sidekiq starts, connects to Redis, but immediately crashes with the following error:

ArgumentError: wrong number of arguments (given 1, expected 0)
/gems/connection_pool-3.0.2/lib/connection_pool/timed_stack.rb:62:in `pop'
/gems/sidekiq-7.3.9/lib/sidekiq/scheduled.rb:226:in `initial_wait'

Reason

The connection_pool gem has been updated to version 3.0, where the API of the pop method has changed - it no longer accepts arguments. Sidekiq 7.3.x still calls it the old way, with an argument.

Bundler automatically pulls in the latest version of connection_pool, and the Sidekiq scheduler crashes immediately.

Fix

Add a version constraint in the Gemfile:

gem 'connection_pool', '~> 2.4'

Then:

bundle update connection_pool

This will install the latest compatible version (2.5.5), and Sidekiq will work correctly.

If your Sidekiq starts but immediately crashes with ArgumentError in connection_pool - check the version. This is a classic case where a transitive dependency breaks everything without any changes in your code.

Like it?React