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async_variant_generation

⚡ Asynchronous Variant Generation & Caching Strategy​

Pre-generate heavy image variants in background jobs and serve them from cache to avoid on‑the‑fly CPU spikes. Use Sidekiq (or your preferred queue) to call .processed and store the result in Redis or CDN.

  1. Enqueue variant processing after attach:
# app/models/photo.rb
class Photo < ApplicationRecord
  has_one_attached :image
  after_commit :enqueue_variants, on: :create

  VARIANTS = {
    thumb: { resize_to_limit: [150, 150] },
    preview: { resize_to_limit: [800, 600] }
  }

  def enqueue_variants
    VARIANTS.each_key do |name|
      ProcessVariantJob.perform_async(id, name)
    end
  end
end
  1. Background job to process & cache:
# app/jobs/process_variant_job.rb
class ProcessVariantJob
  include Sidekiq::Worker
  def perform(photo_id, variant_key)
    photo = Photo.find(photo_id)
    v = photo.image.variant(Photo::VARIANTS[variant_key]).processed
    Rails.cache.write("photo_#{photo_id}_#{variant_key}", v.key, expires_in: 12.hours)
  end
end
  1. Serve cached variant in your controller:
def show
  key = Rails.cache.read("photo_#{params[:id]}_#{params[:variant]}")
  redirect_to rails_blob_url(key, disposition: 'inline')
end