I've set up a small cluster at home via Docker Swarm. I use it to not only an environment to prototype more complex apps, but also keep my devops knowledge up, too.
I originally had a Cluster Hat (https://clusterhat.com/) which piggybacked four Pi-0's on a Pi 3. Even cut out a nice acrylic case, too (https://climbers.net/sbc/clusterhat-review-raspberry-pi-zero...). It worked fine, and I even had Hadoop running on it for a while. The biggest issue was the ARM7 of the host (pi3) vs the ARM6 of the Zero's. This caused a lot of problems with deployments, essentially eliminating the redundancy you get from orchestration systems.