Try to find a way to automatically set SystemMaxUse for systemd-journald.service. I knew I can set it in /etc/systemd/journald.conf manually. But it will restore to default after CoreOS updates in my experience.
Also, configuring drop-ins in cloud-config does not work because the default service definition file does not contain the SystemMaxUse field.
Is there a way to configure journald.conf through cloud config on CoreOS ? Or, is there a way to automatically set it ?