3.6.3 is the version included with this particular software stack, running on CentOS 6.5. 4GB RAM, 2GB currently assigned to Aerospike. Hm, we were informed that at midnight UTC, it will check and resync the cluster, causing a brief spike in CPU load.
Rebooting the principal server helped for a couple of days as described here, but after that the cluster splintered and couldn’t recover for nearly three hours due to suddenly high CPU load as seen when resyncing.