
curl -X POST http://etcd1:2379/v3/cluster/member/add -d '{"peerURLs":["http://etcd4:2380"]}'
Deploy this template, then verify:
curl -X POST http://etcd1:2379/v3/cluster/member/list
Update ETCD3_HOSTS in all Patroni services to include the new node:
etcd1:2379,etcd2:2379,etcd3:2379,etcd4:2379