Disaster Recovery

etcd database backs Kubernetes control plane state, so if the etcd service is unavailable Kubernetes control plane goes down, and the cluster is not recoverable until etcd is recovered with contents. The etcd consistency model builds around the consensus protocol Raft, so for highly-available control plane clusters, loss of one control plane node doesn’t impact cluster health. In general, etcd stays up as long as a sufficient number of nodes to maintain quorum are up. For a three control plane node Talos cluster, this means that the cluster tolerates a failure of any single node, but losing more than one node at the same time leads to complete loss of service. Because of that, it is important to take routine backups of etcd state to have a snapshot to recover cluster from in case of catastrophic failure.

Backup

Snapshotting etcd Database

Create a consistent snapshot of etcd database with talosctl etcd snapshot command:

$ talosctl -n <IP> etcd snapshot db.snapshot
etcd snapshot saved to "db.snapshot" (2015264 bytes)
snapshot info: hash c25fd181, revision 4193, total keys 1287, total size 3035136

Note: filename db.snapshot is arbitrary.

This database snapshot can be taken on any healthy control plane node (with IP address <IP> in the example above), as all etcd instances contain exactly same data. It is recommended to configure etcd snapshots to be created on some schedule to allow point-in-time recovery using the latest snapshot.

Disaster Database Snapshot

If etcd cluster is not healthy, the talosctl etcd snapshot command might fail. In that case, copy the database snapshot directly from the control plane node:

talosctl -n <IP> cp /var/lib/etcd/member/snap/db .

This snapshot might not be fully consistent (if the etcd process is running), but it allows for disaster recovery when latest regular snapshot is not available.

Machine Configuration

Machine configuration might be required to recover the node after hardware failure. Backup Talos node machine configuration with the command:

talosctl -n IP get mc v1alpha1 -o yaml | yq eval '.spec' -

Recovery

Before starting a disaster recovery procedure, make sure that etcd cluster can’t be recovered:

• get etcd cluster member list on all healthy control plane nodes with talosctl -n IP etcd members command and compare across all members.
• query etcd health across control plane nodes with talosctl -n IP service etcd.

If the quorum can be restored, restoring quorum might be a better strategy than performing full disaster recovery procedure.

Latest Etcd Snapshot

Get hold of the latest etcd database snapshot. If a snapshot is not fresh enough, create a database snapshot (see above), even if the etcd cluster is unhealthy.

Init Node

Make sure that there are no control plane nodes with machine type init:

$ talosctl -n <IP1>,<IP2>,... get machinetype
NODE         NAMESPACE   TYPE          ID             VERSION   TYPE
172.20.0.2   config      MachineType   machine-type   2         controlplane
172.20.0.4   config      MachineType   machine-type   2         controlplane
172.20.0.3   config      MachineType   machine-type   2         controlplane

Nodes with init type are incompatible with etcd recovery procedure. init node can be converted to controlplane type with talosctl edit mc --on-reboot command followed by node reboot with talosctl reboot command.

Preparing Control Plane Nodes

If some control plane nodes experienced hardware failure, replace them with new nodes. Use machine configuration backup to re-create the nodes with the same secret material and control plane settings to allow workers to join the recovered control plane.

If a control plane node is healthy but etcd isn’t, wipe the node’s EPHEMERAL partition to remove the etcd data directory (make sure a database snapshot is taken before doing this):

talosctl -n <IP> reset --graceful=false --reboot --system-labels-to-wipe=EPHEMERAL

At this point, all control plane nodes should boot up, and etcd service should be in the Preparing state.

Kubernetes control plane endpoint should be pointed to the new control plane nodes if there were any changes to the node addresses.

Recovering from the Backup

Make sure all etcd service instances are in Preparing state:

$ talosctl -n <IP> service etcd
NODE     172.20.0.2
ID       etcd
STATE    Preparing
HEALTH   ?
EVENTS   [Preparing]: Running pre state (17s ago)
         [Waiting]: Waiting for service "cri" to be "up", time sync (18s ago)
         [Waiting]: Waiting for service "cri" to be "up", service "networkd" to be "up", time sync (20s ago)

Execute the bootstrap command against any control plane node passing the path to the etcd database snapshot:

$ talosctl -n <IP> bootstrap --recover-from=./db.snapshot
recovering from snapshot "./db.snapshot": hash c25fd181, revision 4193, total keys 1287, total size 3035136

Note: if database snapshot was copied out directly from the etcd data directory using talosctl cp, add flag --recover-skip-hash-check to skip integrity check on restore.

Talos node should print matching information in the kernel log:

recovering etcd from snapshot: hash c25fd181, revision 4193, total keys 1287, total size 3035136
{"level":"info","msg":"restoring snapshot","path":"/var/lib/etcd.snapshot","wal-dir":"/var/lib/etcd/member/wal","data-dir":"/var/lib/etcd","snap-dir":"/var/li}
{"level":"info","msg":"restored last compact revision","meta-bucket-name":"meta","meta-bucket-name-key":"finishedCompactRev","restored-compact-revision":3360}
{"level":"info","msg":"added member","cluster-id":"a3390e43eb5274e2","local-member-id":"0","added-peer-id":"eb4f6f534361855e","added-peer-peer-urls":["https:/}
{"level":"info","msg":"restored snapshot","path":"/var/lib/etcd.snapshot","wal-dir":"/var/lib/etcd/member/wal","data-dir":"/var/lib/etcd","snap-dir":"/var/lib/etcd/member/snap"}

Now etcd service should become healthy on the bootstrap node, Kubernetes control plane components should start and control plane endpoint should become available. Remaining control plane nodes join etcd cluster once control plane endpoint is up.

Single Control Plane Node Cluster

This guide applies to the single control plane clusters as well. In fact, it is much more important to take regular snapshots of the etcd database in single control plane node case, as loss of the control plane node might render the whole cluster irrecoverable without a backup.