Comment 3 for bug 1921797

> I can clearly see via querying etcd that the V2 keys all seem related to Flannel, and thus I'm suspecting they're using the /usr/local/bin/etcdctl binary.

Flannel itself uses a golang lib, and only supports ETCD v2. It will likely never support ETCD v3. That etcdctl binary (which is woefully out of date) is only used by the charm for initial configuration of Flannel.

> If I copy the etcdctl from one of the flannel charms onto one of the etcd units for the sake of running "etcdctl backup", it fails

You should be able to do this with the etcd 3.4 client by setting the ETCDCTL_API=2 environment variable: `ETCDCTL_API=2 etcdctl backup ...`