Assets issue when rendering from background job

[Diego Marcet]

Hey guys,

We're having some issues not specifically related to render_anywhere but you may be able to shed some light on them.

In our rails 3.2 app, we're using a Sidekiq job for refreshing cache on the background, below is the snippet for the base class and one of the workers:

require 'render_anywhere'

module CacheRenderer
  class Base
    include Sidekiq::Worker
    include RenderAnywhere
  end
end

# ------------------------------------

module CacheRenderer
  class RecentEventRsvps < Base
    #do not enqueue a rendering job more than once for the same petition over a 2 minute period
    sidekiq_options unique: true, unique_job_expiration: 2 * 60

    def perform(event_id)
      event = Event.find(event_id)
      content_to_cache = render(partial: 'shared/attendees_carousel', locals: { ... })
      Rails.cache.write(['recent_event_rsvps', event.cache_key], content_to_cache)
    end
  end
end

Now this is rendered just fine in development, where assets are not precompiled, but in other environments a AssetNotPrecompiledError exception is risen for an image referenced from an image_tag. Doing some debugging we found that Rails.application.config.assets.digests is nil when the job is ran. Assets are synced to S3 using asset_sync.
Have you ever seen this kind of issues? Do you know if we need to perform any manual initialization for sprockets on the sidekiq job?

Thanks in advance,
Diego.

[Robbie Clutton]

Is your Sidekiq process loading all of Rails, or just some portions of your application? If it's loading all of Rails it should load everything it needs. If it's a portion, there may be some initializers you need to include.

I've also seen issues before if there's an asset host, say if a CDN is being used. Are you using one?

[Diego Marcet]

We're loading the full app; but the issue might be on the CDN (Cloudfront), is there an extra step required to reference the assets on a different host?

Another thing that I realized it may be important is that the sidekiq workers are running on a separated server which doesn't run assets precompilation (the assets are precompiled on the web app servers and uploaded to S3 through the asset_sync gem).

[Robbie Clutton]

I think you'll want config.assets.compile = false in your config, and also set the CDN config.action_controller.asset_host = "cdn.domain.com". Then it shouldn't even try to compile it.