I've tried various combinations of the following, but none worked
file = dir.files.create(
:key => file_name,
:body => io_obj,
:public => true,
'Cache-Control' => "max-age=#{(60 * 60 * 24 * 30 * 6).to_s}"
)
Whilst I haven't tested this explicitly on Rackspace Cloud, this is what I have been using (successfully) for my S3 uploads with Fog:
file = dir.files.create({
:key => filename
:body => File.open(filename),
:public => true,
:metadata => {'Cache-Control' => 'max-age=315576000'}
})