Instructions for setting up a Kubernetes cluster.

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The state of a Kubernetes cluster is kept in the etcd datastore. This page shows how to backup and restore the etcd shipped with the Canonical Distribution of Kubernetes. Backing up application specific data, normally stored in a persistent volume, is outside the scope of this document.

Before you begin

This page assumes you have a working Juju deployed cluster.

Snapshot etcd data

The snapshot action of the etcd charm allows the operator to snapshot a running cluster’s data for use in cloning, backing up, or migrating to a new cluster.

juju run-action etcd/0 snapshot 

This will create a snapshot in /home/ubuntu/etcd-snapshots by default.

Restore etcd data

The etcd charm is capable of restoring its data from a cluster-data snapshot via the restore action. This comes with caveats and a very specific path to restore a cluster: The cluster must be in a state of only having a single member. So it’s best to deploy a new cluster using the etcd charm, without adding any additional units.

juju deploy etcd new-etcd

The above code snippet will deploy a single unit of etcd, as ‘new-etcd’

juju run-action etcd/0 restore target=/mnt/etcd-backups

Once the restore action has completed, evaluate the cluster health. If the unit is healthy, you may resume scaling the application to meet your needs.

Migrating an etcd cluster

Using the above snapshot and restore operations, migrating etcd is a fairly easy task.

Step 1: Snapshot your existing cluster. This is encapsulated in the snapshot action.

juju run-action etcd/0 snapshot


Action queued with id: b46d5d6f-5625-4320-8cda-b611c6ae580c

Step 2: Check the status of the action so you can grab the snapshot and verify the sum. The copy.cmd result output is a copy/paste command for you to download the exact snapshot that you just created.

Download the snapshot archive from the unit that created the snapshot and verify the sha256 sum

juju show-action-output b46d5d6f-5625-4320-8cda-b611c6ae580c


    cmd: juju scp etcd/0:/home/ubuntu/etcd-snapshots/etcd-snapshot-2016-11-09-02.41.47.tar.gz
    path: /home/ubuntu/etcd-snapshots/etcd-snapshot-2016-11-09-02.41.47.tar.gz
    sha256: 1dea04627812397c51ee87e313433f3102f617a9cab1d1b79698323f6459953d
    size: 68K
status: completed

Copy the snapshot to the local disk and then check the sha256sum.

juju scp etcd/0:/home/ubuntu/etcd-snapshots/etcd-snapshot-2016-11-09-02.41.47.tar.gz .
sha256sum etcd-snapshot-2016-11-09-02.41.47.tar.gz

Step 3: Deploy the new cluster leader, and attach the snapshot:

juju deploy etcd new-etcd --resource snapshot=./etcd-snapshot-2016-11-09-02.41.47.tar.gz

Step 4: Reinitialize the master with the data from the resource we just attached in step 3.

juju run-action new-etcd/0 restore

Known Limitations

Loss of PKI warning

If you destroy the leader - identified with the * text next to the unit number in status: all TLS pki will be lost. No PKI migration occurs outside of the units requesting and registering the certificates.

Caution: Mismanaging this configuration will result in locking yourself out of the cluster, and can potentially break existing deployments in very strange ways relating to x509 validation of certificates, which affects both servers and clients.

Restoring from snapshot on a scaled cluster

Restoring from a snapshot on a scaled cluster will result in a broken cluster. Etcd performs clustering during unit turn-up, and state is stored in Etcd itself. During the snapshot restore phase, a new cluster ID is initialized, and peers are dropped from the snapshot state to enable snapshot restoration. Please follow the migration instructions above in the restore action description.


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