Patroni with etcd starting up
Thanks to CyberDem0n.  

Two issues in etcd1 start command:  

API VERSION
Etcd v3.4 default API version is v3.
Patroni doesn't currently support the v3 API.
Etcd 3.4 turned API v2 off by default.

I added --enable-v2=true flag on the three etcd.service and this error was fixed.  

advertise-client-urls FLAG

And for each etcd server I replaced 0.0.0.0 by the real etcd server ip on the --advertise-client-urls flag (like --advertise-client-urls http://10.B.B.99:2379 in the example).