To create a backup (a snapshot) of the current status of your cluster, first download the new version of etcdctl from the website:
wget https://github.com/coreos/etcd/releases/download/v3.2.0/etcd-v3.2.0-linux-amd64.tar.gz tar xvf etcd-v3.2.0-linux-amd64.tar.gz
Once untarred, the folder will contain the new version of the etcdctl executable. To create a snapshot, run the following command:
ETCDCTL_API=3 ./etcdctl snapshot save snapshot.db
This will create a snapshot.db file in the current directory. Do not omit the ETCDCTL_API environment variable, it defines the version of the API etcdctl will use to connect to the ETCD server.