How to retrieve attachment url with Rails Active Storage with S3

Question

rails version 5.2

I have a scenario that I need to access the public url of Rails Active Storage with Amazon s3 to make a zip file with Sidekiq bac

Answer 1

My use case was to upload images to S3 which would have public access for ALL images in the bucket so a job could pick them up later, regardless of request origin or URL expiry. This is how I did it. (Rails 5.2.2)

First, the default for new S3 bucked is to keep everything private, so to defeat that there are 2 steps.

1. Add a wildcard bucket policy. In AWS S3 >> your bucket >> Permissions >> Bucket Policy

{
    "Version": "2008-10-17",
    "Statement": [
        {
            "Sid": "AllowPublicRead",
            "Effect": "Allow",
            "Principal": "*",
            "Action": "s3:GetObject",
            "Resource": "arn:aws:s3:::your-bucket-name/*"
        }
    ]
}

2. In your bucket >> Permissions >> Public Access Settings, be sure Block public and cross-account access if bucket has public policies is set to false

Now you can access anything in your S3 bucket with just the blob.key in the url. No more need for tokens with expiry.

Second, to generate that URL you can either use the solution by @Christian_Butzke: @post.header_image.service.send(:object_for, @post.header_image.key).public_url

However, know that object_for is a private method on service, and if called with public_send would give you an error. So, another alternative is to use the service_url per @George_Claghorn and just remove any params with a url&.split("?")&.first. As noted, this may fail in localhost with a host missing error.

Here is my solution or an uploadable "logo" stored on S3 and made public by default:

#/models/company.rb
has_one_attached :logo
def public_logo_url
    if self.logo&.attachment
        if Rails.env.development?
            self.logo_url = Rails.application.routes.url_helpers.rails_blob_url(self.logo, only_path: true)
        else
            self.logo_url = self.logo&.service_url&.split("?")&.first
        end
    end
    #set a default lazily
    self.logo_url ||= ActionController::Base.helpers.asset_path("default_company_icon.png")
end

Enjoy ^_^