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Syncing files from AWS S3 to local storage on Rails

lucaskuhn profile image Lucas Kuhn ・1 min read

I usually use Amazon S3 for storing images with Active Storage. There are some issues when pulling my database to work with it on localhost:

  • I don't want to accidentally delete something on S3
  • I don't want my localhost without images 🥲

I added this rake task to download files from S3 and format them in a way that works with local storage:

# lib/tasks/s3_to_local.rake 
desc "Sync files from S3 bucket to local storage folder"

task :s3_to_local do

  s3_bucket = "YOUR_S3_BUCKET"
  access_key_id = Rails.application.credentials.dig(:aws, :access_key_id)
  secret_access_key = Rails.application.credentials.dig(:aws, :secret_access_key)

  storage_folder = Rails.root.join('storage')
  storage_folder.mkpath

  system("AWS_ACCESS_KEY_ID=#{access_key_id} AWS_SECRET_ACCESS_KEY=#{secret_access_key} aws s3 sync s3://#{s3_bucket} #{storage_folder}")

  # Ignores sub_folders already created and .keep files
  images = storage_folder.children.select { |file| file.file? && !file.empty? }

  # Formats the file path of each image so ActiveStorage understands them using :local storage
  images.each do |path_name|
    dir, basename = path_name.split
    file_name = basename.to_s
    sub_folders = dir.join(file_name[0..1], file_name[2..3])
    sub_folders.mkpath # Create the subfolder used by active_record
    path_name.rename(dir + sub_folders + basename) # Renames file to be moved into subfolder
  end

end
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What makes this tricky is that S3 storage has everything in the root of the bucket, and when using local storage with ActiveStorage, everything should be under a subfolder.

Also, you need AWS CLI for this to work:

brew install awscli
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Basically copy this task into lib/tasks/s3_to_local.rake, add your bucket name, your AWS credentials, run rake s3_to_local and you're good to go

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