I am not sure what the difference between Redis and S3 is. And if they are different, what are the ways in which they can interact?
I am aware the Redis is a key-value data store and S3 is an online web storage. To me, that sounds very similar though. Is there a difference?
They are completely different things.
Redis is a key-value data store as you say; S3 is a place to place files, to put it simple.
You don’t treat physical files the same way as you treat databases.