I create the cluster template with the following command :

openstack coe cluster template create swarm-clustergp27 \
                     --image fedora-magnum-27-4 \
                     --external-network 566 \
                     --dns-nameserver 10.102.184.2 \
                     --master-flavor m1.small \
                     --flavor m1.small \
                     --coe swarm \
                     --http-proxy http://10.102.162.12:3128 \
                     --https-proxy http://10.102.162.12:3128 \
                     --docker-volume-size 20

It creates the stack and completes it but loggin in the master node it reports in cloudinit logs that etcd package is missing.

What about swarm-mode ?