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atomic_directory_swap

⚙️ Atomic Directory Updates Using Temporary Directories​

For zero-downtime deployments or safe configuration updates, stage changes in a temp directory and then atomically swap it with File.rename. This ensures consumers never see a half-written state.

require 'fileutils'
require 'tmpdir'

def atomic_update(target_dir)
  Dir.mktmpdir(File.basename(target_dir), File.dirname(target_dir)) do |tmp|  
    tmp_path = Pathname.new(tmp)
    # Stage new files
    FileUtils.cp_r('build/output/.', tmp_path)

    # Optionally set permissions or post-process
    tmp_path.children.each { |p| FileUtils.chmod(0o644, p) if p.file? }

    # Atomic swap: move old out, bring new in
    backup = "#{target_dir}.bak"
    FileUtils.rm_rf(backup)
    FileUtils.mv(target_dir, backup)
    FileUtils.mv(tmp_path, target_dir)

    # Cleanup backup if all good
    FileUtils.rm_rf(backup)
  end
end

# Usage
atomic_update('/var/www/my_app/shared/config')

By leveraging Dir.mktmpdir and FileUtils.mv, you guarantee either the old directory or the new one is fully in place, avoiding partial states and ensuring rollback on failure.