Rails, Tailwindcss and Kamal on Apple Silicon
I spent some time trying to get tailwindcss-rails to work with Apple Silicon (M4). The default Rails setup didn’t work for me and I had to find a workaround. This post will show you how to fix it if you run into the same issue.
The problem
By default tailwindcss-rails gem will rely on a self-contained tailwindcss executable. Its architecture is inferred from tailwindcss-ruby gem. While deploying with Kamal, if you are targeting amd64 (as is quite common), the error you would get is something like:
> [build 6/6] RUN SECRET_KEY_BASE_DUMMY=1 ./bin/rails assets:precompile --trace:
0.893 /usr/local/bundle/ruby/3.3.0/gems/railties-8.0.1/lib/rails/command.rb:150:in `invoke_rake'
0.893 /usr/local/bundle/ruby/3.3.0/gems/railties-8.0.1/lib/rails/command.rb:67:in `block in invoke'
0.893 /usr/local/bundle/ruby/3.3.0/gems/railties-8.0.1/lib/rails/command.rb:143:in `with_argv'
0.893 /usr/local/bundle/ruby/3.3.0/gems/railties-8.0.1/lib/rails/command.rb:63:in `invoke'
0.893 /usr/local/bundle/ruby/3.3.0/gems/railties-8.0.1/lib/rails/commands.rb:18:in `<main>'
0.893 /usr/local/lib/ruby/3.3.0/bundled_gems.rb:75:in `require'
0.893 /usr/local/lib/ruby/3.3.0/bundled_gems.rb:75:in `block (2 levels) in replace_require'
0.893 /usr/local/bundle/ruby/3.3.0/gems/bootsnap-1.18.4/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:30:in `require'
0.893 ./bin/rails:4:in `<main>'
0.893 Tasks: TOP => assets:precompile => tailwindcss:build
------
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 --trace
50 |
51 |
--------------------
ERROR: failed to solve: process "/bin/sh -c SECRET_KEY_BASE_DUMMY=1 ./bin/rails assets:precompile --trace" did not complete successfully: exit code: 1
Upon closer inspection you will see that the tailwindcss executable returns an Illegal instruction error within the Docker build. It seems like Rosetta isn’t able to run the tailwindcss executable inside the Docker build.
The solution
The first solution that made the trick for me was to switch the Docker virtualization from Apple Virtualization Framework to Docker VMM:
Docker VMM is in BETA at this point though and I got some buggy behaviour in other steps of the build (bootsnap got stuck forever) so my long-term solution was to introduce tailwindcss through Bun:
# add tailwindcss and its CLI to your project
bun add -d tailwindcss @tailwindcss/cli
# tell tailwindcss-ruby gem to find the executable in the node_modules
export TAILWINDCSS_INSTALL_DIR=node_modules/.bin
P.D. if you also rely on Bun and don’t have a Node runtime in your Rails build you might find the following hack handy:
ln -s $(which bun) /usr/local/bin/node
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