I'd say security is his biggest pain. Redis is insecure by default[1].
That's a pretty low blow. Redis is insecure because it is designed that way, it is a powertool with a very specific role to fill and it comes with a very nice warning to that effect. If you use it in a way that's insecure the problem is yours, not redis'.
Compare with cooks knives, powertools (drills, reciprocal saws and circular saws as well as fun things such as plasma cutters, welding gear, chainsaws, hedge trimmers, lathes and mills) and other professional tools sold without any kind of license or requirements of proficiency by stores all over the world.
Each and every one of those can kill you, in a pretty straightforward manner. And yet, they continue to be shipped, insecure by default. Because their users will not be able to do their jobs if each and every one of those would come with the kind of safety requirements that we'd normally apply to say a toy for a toddler.
If you don't know how to use a tool like redis in a secure way then you probably have other problems besides.
You'd probably be shocked to hear that many cluster environments have a single gateway machine that is (usually somewhat) secure but behind that gateway the whole cluster is wide open.
Not only your comment is off topic, it's also comment is short-sighted at best. Redis is a fantastic tool that helps professionals like me get work done. It's well designed, well maintained, well written (just read the source code), and is one of the few small open source projects you can introduce to big co without fearing upper management complaints.
So yeah, maybe it's not as secure as you wish by default, but I'm glad antirez has the priority sense he has, because it led to working software that you can easily secure in your architecture.
So no, I don't think security is his biggest pain.