CarrierWave Backgrounder

NOTICE: Version 1.0.0 contains breaking changes if you are coming from an earlier version.
The most notible change is the removal of queue backend options other than active_job and sidekiq.
If you are using other backends, switch over to active_job which should support your preference.
If you are using Sidekiq, there is nothing to change.

I am a fan of CarrierWave. That being said, I don’t like tying up requests waiting for images to process.

This gem addresses that by offloading processing or storaging/processing to a background task.
We currently support ActiveJob and Sidekiq.

Background options

There are currently two offerings for backgrounding upload tasks which are as follows;

# This stores the original file with no processing/versioning.
# It will upload the original file to s3.
# This was developed to use in cases where you do not have access to the cached location such as Heroku.

Backgrounder::ORM::Base::process_in_background

# This does nothing to the file after it is cached which makes it fast.
# It requires a column in the database which stores the cache location set by carrierwave so the background job can access it.
# The drawback to using this method is the need for a central location to store the cached files.
#
# IMPORTANT: Only use this method if you have full control over your tmp storage directory and can mount it on every deployed server.

Backgrounder::ORM::Base::store_in_background

Installation and Usage

These instructions assume you have previously set up CarrierWave and your queuing lib of choice.

Take a look at the Rails app to see examples of setup.

In Rails, add the following your Gemfile:

gem 'carrierwave_backgrounder'

Run the generator which will create an initializer in config/initializers.

rails g carrierwave_backgrounder:install

You can pass additional configuration options to Sidekiq:

CarrierWave::Backgrounder.configure do |c|
  c.backend :sidekiq, queue: :awesome_queue, size: 3
end

IMPORTANT FOR SIDEKIQ BACKEND - carrierwave (default queue name) should be added to your queue list or it will not run:

:queues:
  - [carrierwave, 1]
  - default

In your CarrierWave uploader file you will need to add a cache directory as well as change cache_storage to File:

class AvatarUploader < CarrierWave::Uploader::Base
  include ::CarrierWave::Backgrounder::Delay

  # This is required if you are using S3 or any other remote storage.
  # CarrierWave's default is to store the cached file remotely which is slow and uses bandwidth.
  # By setting this to File, it will only store on saving of the record.
  cache_storage CarrierWave::Storage::File

  # It is recommended to set this to a persisted location if you are using `::store_in_background`.
  def cache_dir
    "path/that/persists"
  end

  #etc...
end

To use process_in_background

In your model:

mount_uploader :avatar, AvatarUploader
process_in_background :avatar

Optionally you can add a column to the database which will be set to true when
the background processing has started and to false when the background processing is complete.

This is set to true in the after_commit hook when the job is created. It is very useful if you are waiting to notify the user of completion.

add_column :users, :avatar_processing, :boolean, null: false, default: false

To use store_in_background

In your model:

mount_uploader :avatar, AvatarUploader
store_in_background :avatar

Add a column to the model which will store the temp file location:

add_column :users, :avatar_tmp, :string

Usage Tips

Bypass backgrounding

If you need to process/store the upload immediately:

@user.process_<column>_upload = true

This must be set before you assign an upload:

@user = User.new
@user.process_avatar_upload = true
@user.attributes = params[:user]

Override worker

To override the worker in cases where additional methods need to be called or you have app specific requirements, pass the worker class as the second argument:

process_in_background :avatar, MyParanoidWorker

Then create a worker that subclasses carrierwave_backgrounder’s worker.
Each method, #store_in_background and #process_in_background has there own worker.

For Sidekiq

process_in_background subclass ::CarrierWave::Workers::ProcessAsset
store_in_background subclass ::CarrierWave::Workers::StoreAsset

For ActiveJob

process_in_background subclass ::CarrierWave::Workers::ActiveJob::ProcessAsset
store_in_background subclass ::CarrierWave::Workers::ActiveJob::StoreAsset

# Sidekiq Example

class User < ActiveRecord::Base
  mount_uploader :avatar, AvatarUploader
  process_in_background :avatar, MyParanoidWorker
end

class MyParanoidWorker < ::CarrierWave::Workers::ProcessAsset
  # ...or subclass CarrierWave::Workers::StoreAsset if you're using store_in_background

  def error(job, exception)
    report_job_failure  # or whatever
  end

  # other hooks you might care about
end

# ActiveJob Example

class User < ActiveRecord::Base
  mount_uploader :avatar, AvatarUploader
  process_in_background :avatar, MyActiveJobWorker
end

class MyActiveJobWorker < ::CarrierWave::Workers::ActiveJob::StoreAsset
  after_perform do
    # your code here
  end
end

Testing with Rspec

We use the after_commit hook when using active_record. This creates a problem when testing with Rspec because after_commit never gets fired
if you’re using transactional fixtures. One solution to the problem is to use the TestAfterCommit gem.
There are various other solutions in which case google is your friend.

License

Copyright © 2011 Larry Sprock

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
“Software”), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.