Just holding the two Redis connections makes sense. I remember the Postgres post said something about modifying HTTP headers (a solution I liked), and I didn't know if this would be something similar.
Actually, I just looked back, and that was to solve the problem of only being able to write to a single postgres instance of the globally distributed cluster. For just caching, with every instance writeable, that probably wouldn't apply here.
I think the main difference is that by making replicas writable you lose the ability to have redis throw an error like Postgres does when you try to write to a replica. The upside is that you can write to replicas when you don’t need a global write without rerouting the request somewhere else, the downside is that your app has to have that knowledge about which one to use in which situations. It’s definitely an interesting set of trade offs for the two use cases!
