That works for me. You are setting a value for for the access keys, right?
What makes you think that this is the case? You can replace DRY_RUN=1 rake uploads:migrate_to_s3 with rails c in the above command and inspect the values of the settings if you want to see what’s happening…
It must be the url column in the topic_links table. It’s the only column with a restriction of 500 chars.