Does it still make sense to setup your own failover system (HAproxy + 2 or more servers for example) when self healing cloud seems like a practical solution? They seem to do the same job or am I missing something?
You're missing something. Specifically, the difference between High Availability (and the degrees thereof) and High Capacity/Scalability.
A "self-healing cloud server" (also known as "a machine that reboots itself" -- hardly high technology worthy of the grandiose marketing term) provides you some degree of high availability against a small subset of possible problems -- namely, hardware/kernel failure. Now, whilst hardware does fail, it is the second-least common cause of downtime (if you're wondering, core network outages are the least-common). All the common causes of outages -- system maintenance, human error -- are still lurking there, ready to take you down.
Also, a machine that reboots when it crashes still has some downtime, it's just not as much as it would be if you had to manually login and start the machine again yourself. This may be an acceptable level of downtime, or it may not. I don't know what your tolerances are.
Finally, this doesn't provide you with any capacity for seamless scalability. Sure, you can throw more hardware at the problem (up to a point), but that requires a reboot, too, and it only gets you as far as you can go with a single machine -- if you need to service more traffic, you're up for a re-engineering.
Now, it's entirely possible that you don't need particularly high uptime, or scalability, and so a single machine that reboots itself might be fine. If that's the case, more power to you. But don't think that it's a replacement for a cluster of machines behind a redundant load balancer, properly engineered for availability and capacity, because it's a whole different ball game.
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