How do you deal with failures? What happens if the redid availability zone disappears for example? An I manually responsible for recovery and backups in this cases, or do you use redis as a cache that can be recovered from s3?
Redis is used to persistent metadata, it can not be recovered from S3. The hosted Redis solution should already have failover solution for that, for example, AWS ElasticCache have multi-AZ failover[1].
[1] https://docs.aws.amazon.com/AmazonElastiCache/latest/red-ug/...