What would happen if systemd is used to manage a cluster resource?
You must not manage services managed by a cluster resource with systemd. The cluster will try to “fix the problem” e.g. if you used systemd to stop apache on a server the cluster monitoring would see apache had failed and try to restart it a number of times, dependent on the cluster resource configuration. If the restart failed, for example and you kept using systemd to stop it again it would reconfigure the cluster, i.e. load apache on another node. Remember the cluster only knows about cluster resources not about systemd units. If you need to manually manage resources on a node set that node to maintenance mode. Maintenance mode on a node means it will not monitor, start or stop resource on that node which allows you to manually manage services to test and troubleshoot. Maintenance mode does not stop or move services running on the node. Other nodes run normally.