Many people abuses Redis as pub/sub queue. I wonder how is Redis topology though. Becuase in a native redis-cluster, keys are hashed. So pub/sub still writes to the same instance if the key is same.
And if the Redis is the enterprise edition or the open-source one. For OSS edition, there needs to be a gateway for HTTP API. More often than not, I saw the client implementation being faulty rather than the Redis itself.
Shopify has a huge scale though, probably smaller issues wound up and become problems...
