Intro

when using activestorage, one could set the ec2 instance with a role with access to certain aws s3 buckets.

In this case, we only define the region and bucket name to allow activestorage to connect to s3.

# in config/storage.yml
some_files:
  service: S3
  region: #{Rails.application.credentials.dig(:aws, :some_files, :region)}
  bucket: #{Rails.application.credentials.dig(:aws, :some_files, :bucket)}

Then if you would like to download or upload something to S3 without having to do it via ActiveStorage you could do the following:

client = Aws::S3::Client.new(region: 'us-east-2')  
resource = Aws::S3::Resource.new(client: client)
bucket = resource.bucket("bucket-name")

# getting a file from the bucket
new_object = bucket.object("some file key")
object = new_object.get

# if you would like to store this file
File.open('my new file name', 'wb') do |file|
  IO.copy_stream(object.body, file)
end