We use Raft as the underlying distributed protocol which provides consistency and persistence of the data across all of the etcd instances.
Let start by creating 3 new etcd instances.
We use `-peer-addr` to specify server port and `-addr` to specify client port and `-data-dir` to specify the directory to store the log and info of the machine in the cluster:
**Note:** If you want to run etcd on an external IP address and still have access locally, you'll need to add `-bind-addr 0.0.0.0` so that it will listen on both external and localhost addresses.
A similar argument `-peer-bind-addr` is used to setup the listening address for the server port.
Let's join two more machines to this cluster using the `-peers` argument. A single connection to any peer will allow a new machine to join, but multiple can be specified for greater resiliency.
If one machine is killed, it could rejoin the cluster when started with old name. If the peer address is changed, etcd will treat the new peer address as the refreshed one, which benefits instance migration, or virtual machine boot with different IP. The peer-address-changing functionality is only supported when the majority of the cluster is alive, because this behavior needs the consensus of the etcd cluster.
**Note:** For now, it is user responsibility to ensure that the machine doesn't join the cluster that has the member with the same name. Or unexpected error will happen. It would be improved sooner or later.
An etcd server is uniquely defined by the peer addresses it listens to. Suppose, however, that you wish to start over, while maintaining the data from the previous cluster -- that is, to pretend that this machine has never joined a cluster before.
You can use `--initial-cluster-name` to generate a new unique ID for each node, as a shared token that every node understands. Nodes also take this into account for bootstrapping the new cluster ID, so it also provides a way for a machine to listen on the same interfaces, disconnect from one cluster, and join a different cluster.