That Weird Rails 8 + Tailwind + Kamal Bug on macOS

Edu Depetris

- Aug 28, 2025
  • Ruby On Rails
  • Tailwindcss
  • Kamal
  • Bug
If you’re deploying a Rails 8 app with Tailwind CSS using Kamal from macOS to a Linux server, chances are you’ll hit one of those head-scratching bugs that make you question everything.

#17 [build 6/6] RUN SECRET_KEY_BASE_DUMMY=1 ./bin/rails assets:precompile
#17 3.110 ≈ tailwindcss v4.1.12
#17 3.110 
#17 3.201 Error: Cannot apply unknown utility class `gap-x-2`
#17 3.207 bin/rails aborted!
#17 3.207 Command failed with exit 1: /usr/local/bundle/ruby/3.3.0/gems/tailwindcss-ruby-4.1.12-x86_64-linux-gnu/exe/x86_64-linux-gnu/tailwindcss
#17 3.207 
#17 3.207 Tasks: TOP => assets:precompile => tailwindcss:build
#17 3.207 (See full trace by running task with --trace)
#17 ERROR: process "/bin/sh -c SECRET_KEY_BASE_DUMMY=1 ./bin/rails assets:precompile" did not complete successfully: exit code: 1

Dockerfile:49
--------------------
  47 |     
  48 |     # Precompiling assets for production without requiring secret RAILS_MASTER_KEY
  49 | >>> RUN SECRET_KEY_BASE_DUMMY=1 ./bin/rails assets:precompile
  50 |     
  51 |     
--------------------
ERROR: failed to build: failed to solve: process "/bin/sh -c SECRET_KEY_BASE_DUMMY=1 ./bin/rails assets:precompile" did not complete successfully: exit code: 1

View build details: docker-desktop://dashboard/build/kamal-local-docker-container/kamal-local-docker-container0/ceiqu1e90hzfs12b68uv5eq20
docker stderr: Nothing written

TLDR;

Open Docker > Settings > General and uncheck Use Rosetta for x86_64/amd64 emulation on Apple Silicon


This Github link provides context about the issue and the solution.
This link will give you a better idea about the weird bug and this one is the workaround.

🎉 Happy deploy!