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+## Disaster recovery
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+
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+etcd is designed to withstand machine failures. An etcd cluster automatically recovers from temporary failures (e.g., machine reboots) and tolerates up to *(N-1)/2* permanent failures for a cluster of N members. When a member permanently fails, whether due to hardware failure or disk corruption, it loses access to the cluster. If the cluster permanently loses more than *(N-1)/2* members then it disastrously fails, irrevocably losing quorum. Once quorum is lost, the cluster cannot reach consensus and therefore cannot continue accepting updates.
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+
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+To recover from disastrous failure, etcd provides snapshot and restore facilities to recreate the cluster without data loss.
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+
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+### Snapshotting the keyspace
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+
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+Recovering a cluster first needs a snapshot of the keyspace from an etcd member. A snapshot may either be taken from a live member with the `etcdctl snapshot save` command or by copying the `member/snap/db` file from an etcd data directory. For example, the following command snapshots the keyspace served by `$ENDPOINT` to the file `snapshot.db`:
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+
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+```sh
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+$ etcdctl --endpoints $ENDPOINT snapshot save snapshot.db
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+```
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+
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+### Restoring a cluster
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+
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+To restore a cluster, all that is needed is a single snapshot "db" file. A cluster restore with `etcdctl snapshot restore` creates new etcd data directories; all members should restore using the same snapshot. Restoring overwrites some snapshot metadata (specifically, the member ID and cluster ID); the member loses its former identity. This metadata overwrite prevents the new member from inadvertently joining an existing cluster. Therefore in order to start a cluster from a snapshot, the restore must start a new logical cluster.
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+
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+A restore initializes a new member of a new cluster, with a fresh cluster configuration using `etcd`'s cluster configuration flags, but preserves the contents of the etcd keyspace. Continuing from the previous example, the following creates new etcd data directories (`m1.etcd`, `m2.etcd`, `m3.etcd`) for a three member cluster:
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+
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+```sh
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+$ etcdctl snapshot restore snapshot.db \
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+ --name m1 \
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+ --initial-cluster m1=http:/host1:2380,m2=http://host2:2380,m3=http://host3:2380 \
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+ --initial-cluster-token etcd-cluster-1 \
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+ --initial-advertise-peer-urls http://host1:2380
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+$ etcdctl snapshot restore snapshot.db \
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+ --name m2 \
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+ --initial-cluster m1=http:/host1:2380,m2=http://host2:2380,m3=http://host3:2380 \
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+ --initial-cluster-token etcd-cluster-1 \
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+ --initial-advertise-peer-urls http://host2:2380
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+$ etcdctl snapshot restore snapshot.db \
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+ --name m3 \
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+ --initial-cluster m1=http:/host1:2380,m2=http://host2:2380,m3=http://host3:2380 \
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+ --initial-cluster-token etcd-cluster-1 \
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+ --initial-advertise-peer-urls http://host3:2380
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+```
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+
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+Next, start `etcd` with the new data directories:
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+
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+```sh
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+$ etcd \
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+ --name m1 \
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+ --listen-client-urls http://host1:2379 \
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+ --advertise-client-urls http://host1:2379 \
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+ --listen-peer-urls http://host1:2380 &
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+$ etcd \
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+ --name m2 \
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+ --listen-client-urls http://host2:2379 \
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+ --advertise-client-urls http://host2:2379 \
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+ --listen-peer-urls http://host2:2380 &
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+$ etcd \
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+ --name m3 \
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+ --listen-client-urls http://host3:2379 \
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+ --advertise-client-urls http://host3:2379 \
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+ --listen-peer-urls http://host3:2380 &
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+```
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+
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+Now the restored etcd cluster should be available and serving the keyspace given by the snapshot.
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+
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Anthony Romano