---
reviewers:
- sig-cluster-lifecycle
title: Set up a Highly Availabile etcd Cluster With kubeadm
content_template: templates/task
---

{{% capture overview %}}

Kubeadm defaults to running a single member etcd cluster in a static pod managed
by the kubelet on the control plane node. This is not a highly available setup
as the the etcd cluster contains only one member and cannot sustain any members
becoming unavailable. This task walks through the process of creating a highly
available etcd cluster of three members that can be used as an external etcd
when using kubeadm to set up a kubernetes cluster.

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{{% capture prerequisites %}}

* Three hosts that can talk to each other over ports 2379 and 2380. This
  document assumes these default ports. However, they are configurable through
  the kubeadm config file.
* Each host must [have docker, kubelet, and kubeadm installed][toolbox].
* Some infrastructure to copy files between hosts (e.g., ssh).

[toolbox]: /docs/setup/independent/install-kubeadm/

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{{% capture steps %}}

## Setting up the cluster

The general approach is to generate all certs on one node and only distribute
the *necessary* files to the other nodes. Note that kubeadm contains all the
necessary crytographic machinery to generate the certificates described below;
no other cryptographic tooling is required for this example.

1. Create configuration files for kubeadm.

    Generate one kubeadm configuration file for each host that will have an etcd
    member running on it using the following script.

    ```sh
    # Update HOST0, HOST1, and HOST2 with the IPs or resolvable names of your hosts
    export HOST0=10.0.0.6
    export HOST1=10.0.0.7
    export HOST2=10.0.0.8

    # Create temp directories to store files that will end up on other hosts.
    mkdir -p /tmp/${HOST0}/ /tmp/${HOST1}/ /tmp/${HOST2}/

    ETCDHOSTS=(${HOST0} ${HOST1} ${HOST2})
    NAMES=("infra0" "infra1" "infra2")

    for i in "${!ETCDHOSTS[@]}"; do
    HOST=${ETCDHOSTS[$i]}
    NAME=${NAMES[$i]}
    cat << EOF > /tmp/${HOST}/kubeadmcfg.yaml
    apiVersion: "kubeadm.k8s.io/v1alpha2"
    kind: MasterConfiguration
    etcd:
        localEtcd:
            serverCertSANs:
            - "${HOST}"
            peerCertSANs:
            - "${HOST}"
            extraArgs:
                initial-cluster: infra0=https://${ETCDHOST0}:2380,infra1=https://${ETCDHOST1}:2380,infra2=https://${ETCDHOST2}:2380
                initial-cluster-state: new
                name: ${NAME}
                listen-peer-urls: https://${HOST}:2380
                listen-client-urls: https://${HOST}:2379
                advertise-client-urls: https://${HOST}:2379
                initial-advertise-peer-urls: https://${HOST}:2380
    EOF
    done
    ```

1. Generate the certificate authority

    If you already have a CA then the only action that is copying the CA's `crt` and
    `key` file to `/etc/kubernetes/pki/etcd/ca.crt` and
    `/etc/kubernetes/pki/etcd/ca.key`. After those files have been copied, please
    skip this step.

    If you do not already have a CA then run this command on `$HOST0` (where you
    generated the configuration files for kubeadm).

    ```
    kubeadm alpha phase certs etcd-ca
    ```

    This creates two files

    - `/etc/kubernetes/pki/etcd/ca.crt`
    - `/etc/kubernetes/pki/etcd/ca.key`

1. Create certificates for each member

    ```sh
    kubeadm alpha phase certs etcd-server --config=/tmp/${HOST2}/kubeadmcfg.yaml
    kubeadm alpha phase certs etcd-peer --config=/tmp/${HOST2}/kubeadmcfg.yaml
    kubeadm alpha phase certs etcd-healthcheck-client --config=/tmp/${HOST2}/kubeadmcfg.yaml
    kubeadm alpha phase certs apiserver-etcd-client --config=/tmp/${HOST2}/kubeadmcfg.yaml
    cp -R /etc/kubernetes/pki /tmp/${HOST2}/
    # cleanup non-reusable certificates
    find /etc/kubernetes/pki -not -name ca.crt -not -name ca.key -type f -delete

    kubeadm alpha phase certs etcd-server --config=/tmp/${HOST1}/kubeadmcfg.yaml
    kubeadm alpha phase certs etcd-peer --config=/tmp/${HOST1}/kubeadmcfg.yaml
    kubeadm alpha phase certs etcd-healthcheck-client --config=/tmp/${HOST1}/kubeadmcfg.yaml
    kubeadm alpha phase certs apiserver-etcd-client --config=/tmp/${HOST1}/kubeadmcfg.yaml
    cp -R /etc/kubernetes/pki /tmp/${HOST2}/
    find /etc/kubernetes/pki -not -name ca.crt -not -name ca.key -type f -delete

    kubeadm alpha phase certs etcd-server --config=/tmp/${HOST0}/kubeadmcfg.yaml
    kubeadm alpha phase certs etcd-peer --config=/tmp/${HOST0}/kubeadmcfg.yaml
    kubeadm alpha phase certs etcd-healthcheck-client --config=/tmp/${HOST0}/kubeadmcfg.yaml
    kubeadm alpha phase certs apiserver-etcd-client --config=/tmp/${HOST0}/kubeadmcfg.yaml
    # No need to move the certs because they are for HOST0

    # clean up certs that should not be copied off this host
    find /tmp/${HOST2} -name ca.key -type f -delete
    find /tmp/${HOST1} -name ca.key -type f -delete
    ```

1. Copy certificates and kubeadm configs

    The certificates have been generated and now they must be moved to their
    respective hosts.

     ```sh
     USER=ubuntu
     HOST=${HOST1}
     scp -r /tmp/${HOST}/* ${USER}@${HOST}:
     ssh ${USER}@${HOST}
     USER@HOST $ sudo -Es
     root@HOST $ chown -R root:root pki
     root@HOST $ mv pki /etc/kubernetes/
     ```

1. Ensure all expected files exist

    The complete list of required files on `$HOST0` is:

    ```
    /tmp/${HOST0}
    └── kubeadmcfg.yaml
    ---
    /etc/kubernetes/pki
    ├── apiserver-etcd-client.crt
    ├── apiserver-etcd-client.key
    └── etcd
        ├── ca.crt
        ├── ca.key
        ├── healthcheck-client.crt
        ├── healthcheck-client.key
        ├── peer.crt
        ├── peer.key
        ├── server.crt
        └── server.key
    ```

    On `$HOST1`:

    ```
    $HOME
    └── kubeadmcfg.yaml
    ---
    /etc/kubernetes/pki
    ├── apiserver-etcd-client.crt
    ├── apiserver-etcd-client.key
    └── etcd
        ├── ca.crt
        ├── healthcheck-client.crt
        ├── healthcheck-client.key
        ├── peer.crt
        ├── peer.key
        ├── server.crt
        └── server.key
    ```

    On `$HOST2`

    ```
    $HOME
    └── kubeadmcfg.yaml
    ---
    /etc/kubernetes/pki
    ├── apiserver-etcd-client.crt
    ├── apiserver-etcd-client.key
    └── etcd
        ├── ca.crt
        ├── healthcheck-client.crt
        ├── healthcheck-client.key
        ├── peer.crt
        ├── peer.key
        ├── server.crt
        └── server.key
    ```

1. Create the static pod manifests

    Now that the certificates and configs are in place it's time to create the
    manifests. On each host run the `kubeadm` command to generate a static manifest
    for etcd.

    ```sh
    root@HOST0 $ kubeadm alpha phase etcd local --config=/tmp/${HOST0}/kubeadmcfg.yaml
    root@HOST1 $ kubeadm alpha phase etcd local --config=/home/ubuntu/kubeadmcfg.yaml
    root@HOST2 $ kubeadm alpha phase etcd local --config=/home/ubuntu/kubeadmcfg.yaml
    ```

1. Optional: Check the cluster health

    ```sh
    docker run --rm -it \
    --net host \
    -v /etc/kubernetes:/etc/kubernetes quay.io/coreos/etcd:v3.2.18 etcdctl \
    --cert-file /etc/kubernetes/pki/etcd/peer.crt \
    --key-file /etc/kubernetes/pki/etcd/peer.key \
    --ca-file /etc/kubernetes/pki/etcd/ca.crt \
    --endpoints https://${HOST0}:2379 cluster-health
    ...
    cluster is healthy
    ```

{{% /capture %}}

{{% capture whatsnext %}}

Once your have a working 3 member etcd cluster, you can continue setting up a
highly available control plane using the [external etcd method with
kubeadm](/docs/setup/independent/high-availability/).

{{% /capture %}}


