Why Raspberry Pi Cluster?
There seem to be two schools of thought in the homelab community regarding whether Raspberry Pi clusters are worth it. Many are of the thought that four Raspberry Pis, clustered, with all the peripherals like hard drives, networking equipment, power supplies, etc. adds up to be more expensive than a single NUC or blade with way better specs. This seems reasonable and yet I still find myself drawn to the Pi cluster.
Why? Because of resource isolation and balance.
I have four Raspberry Pi 4 B (4gb) hosts running Ubuntu 64bit. I can have one dedicated to running a Bitcoin full node and know that any disk or CPU spike will not interrupt my web hosting on a separate host. I have dedicated and isolated units comprising CPU, RAM, NIC, and HDD resources. This, in some ways, is the opposite of running a true cluster with tools like Kubernetes. In a true cluster environment, the system is agnostic to where services are deployed on the bare metal, with some caveats.
Under normal loads, my Raspberry Pis are not maxing out any system resources except for network bandwidth at times. A perfect case for a CPU per NIC. It's also why I won't be adding an 8gb Pi 4 to my homelab any time soon.
Some other reasons people go with a Pi cluster, unverified by me, are lower power usage, substantially lower costs in some cases, and above all else, it's just fun.