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Creating HA clusters with kubeadm

This guide shows you how to install and set up a highly available Kubernetes cluster using kubeadm.

This document shows you how to perform setup tasks that kubeadm doesn’t perform: provision hardware; configure multiple systems; and load balancing.

Note: This guide is only one potential solution, and there are many ways to configure a highly available cluster. If a better solution works for you, please use it. If you find a better solution that can be adopted by the community, feel free to contribute it back.

Before you begin

Installing prerequisites on masters

For each master that has been provisioned, follow the installation guide on how to install kubeadm and its dependencies. At the end of this step, you should have all the dependencies installed on each master.

Setting up an HA etcd cluster

For highly available setups, you will need to decide how to host your etcd cluster. A cluster is composed of at least 3 members. We recommend one of the following models:

While the first option provides more performance and better hardware isolation, it is also more expensive and requires an additional support burden.

For Option 1: create 3 virtual machines that follow CoreOS’s hardware recommendations. For the sake of simplicity, we will refer to them as etcd0, etcd1 and etcd2.

For Option 2: you can skip to the next step. Any reference to etcd0, etcd1 and etcd2 throughout this guide should be replaced with master0, master1 and master2 accordingly, since your master nodes host etcd.

Create etcd CA certs

  1. Install cfssl and cfssljson on all etcd nodes:

     curl -o /usr/local/bin/cfssl https://pkg.cfssl.org/R1.2/cfssl_linux-amd64
     curl -o /usr/local/bin/cfssljson https://pkg.cfssl.org/R1.2/cfssljson_linux-amd64
     chmod +x /usr/local/bin/cfssl*
  2. SSH into etcd0 and run the following:

     mkdir -p /etc/kubernetes/pki/etcd
     cd /etc/kubernetes/pki/etcd
    
     cat >ca-config.json <<EOF
     {
        "signing": {
            "default": {
                "expiry": "43800h"
            },
            "profiles": {
                "server": {
                    "expiry": "43800h",
                    "usages": [
                        "signing",
                        "key encipherment",
                        "server auth",
                        "client auth"
                    ]
                },
                "client": {
                    "expiry": "43800h",
                    "usages": [
                        "signing",
                        "key encipherment",
                        "client auth"
                    ]
                },
                "peer": {
                    "expiry": "43800h",
                    "usages": [
                        "signing",
                        "key encipherment",
                        "server auth",
                        "client auth"
                    ]
                }
            }
        }
     }
     EOF
     cat >ca-csr.json <<EOF
     {
        "CN": "etcd",
        "key": {
            "algo": "rsa",
            "size": 2048
        }
     }
     EOF
    Optional: You can modify ca-csr.json to add a section for names. See the CFSSL wiki for an example.
  3. Next, generate the CA certs:

     cfssl gencert -initca ca-csr.json | cfssljson -bare ca -

Generate etcd client certs

Generate the client certificates. While on etcd0, run the following:

cat >client.json <<EOF
{
  "CN": "client",
  "key": {
      "algo": "ecdsa",
      "size": 256
  }
}
EOF
cfssl gencert -ca=ca.pem -ca-key=ca-key.pem -config=ca-config.json -profile=client client.json | cfssljson -bare client

Both client.pem and client-key.pem are created.

Create SSH access

In order to copy certs between machines, you must enable SSH access for scp.

  1. First, open new tabs in your shell for etcd1 and etcd2. Ensure you are SSHed into all three machines and then run the following (it will be a lot quicker if you use tmux syncing - to do this in iTerm enter cmd+shift+i):

     export PEER_NAME=$(hostname)
     export PRIVATE_IP=$(ip addr show eth1 | grep -Po 'inet \K[\d.]+')

    Make sure that eth1 corresponds to the network interface for the IPv4 address of the private network. This might vary depending on your networking setup, so please check by running echo $PRIVATE_IP before continuing.

  2. Next, generate some SSH keys for the boxes:

     ssh-keygen -t rsa -b 4096 -C "<email>"

    Make sure to replace <email> with your email, a placeholder, or an empty string. Keep hitting enter until files exist in ~/.ssh.

  3. Output the contents of the public key file for etcd1 and etcd2:

     cat ~/.ssh/id_rsa.pub
  4. Finally, copy the output for each and paste them into etcd0’s ~/.ssh/authorized_keys file. This will permit etcd1 and etcd2 to SSH in to the machine.

Generate etcd server and peer certs

  1. In order to generate certs, each etcd machine needs the root CA generated by etcd0. On etcd1 and etcd2, run the following:

     mkdir -p /etc/kubernetes/pki/etcd
     cd /etc/kubernetes/pki/etcd
     scp root@<etcd0-ip-address>:/etc/kubernetes/pki/etcd/ca.pem .
     scp root@<etcd0-ip-address>:/etc/kubernetes/pki/etcd/ca-key.pem .
     scp root@<etcd0-ip-address>:/etc/kubernetes/pki/etcd/client.pem .
     scp root@<etcd0-ip-address>:/etc/kubernetes/pki/etcd/client-key.pem .
     scp root@<etcd0-ip-address>:/etc/kubernetes/pki/etcd/ca-config.json .

    Where <etcd0-ip-address> corresponds to the public or private IPv4 of etcd0.

  2. Once this is done, run the following on all etcd machines:

     cfssl print-defaults csr > config.json
     sed -i '0,/CN/{s/example\.net/'"$PEER_NAME"'/}' config.json
     sed -i 's/www\.example\.net/'"$PRIVATE_IP"'/' config.json
     sed -i 's/example\.net/'"$PEER_NAME"'/' config.json
     cfssl gencert -ca=ca.pem -ca-key=ca-key.pem -config=ca-config.json -profile=server config.json | cfssljson -bare server
     cfssl gencert -ca=ca.pem -ca-key=ca-key.pem -config=ca-config.json -profile=peer config.json | cfssljson -bare peer

    The above will replace the default configuration with your machine’s hostname as the peer name, and its IP addresses. Make sure these are correct before generating the certs. If you found an error, reconfigure config.json and re-run the cfssl commands.

This results in the following files: peer.pem, peer-key.pem, server.pem, server-key.pem.

Please select one of the tabs to see installation instructions for the respective way to set up a virtual IP.

  1. First, install etcd binaries:

     ETCD_VERSION="v3.1.12" curl -sSL https://github.com/coreos/etcd/releases/download/${ETCD_VERSION}/etcd-${ETCD_VERSION}-linux-amd64.tar.gz | tar -xzv --strip-components=1 -C /usr/local/bin/

    It is worth noting that etcd v3.1.12 is the preferred version for Kubernetes v1.10. For other versions of Kubernetes please consult the changelog.

    Also, please realize that most distributions of Linux already have a version of etcd installed, so you will be replacing the system default.

  2. Next, generate the environment file that systemd will use:

     touch /etc/etcd.env
     echo "PEER_NAME=${PEER_NAME}" >> /etc/etcd.env
     echo "PRIVATE_IP=${PRIVATE_IP}" >> /etc/etcd.env
  3. Now copy the systemd unit file:

     cat >/etc/systemd/system/etcd.service <<EOF
     [Unit]
     Description=etcd
     Documentation=https://github.com/coreos/etcd
     Conflicts=etcd.service
     Conflicts=etcd2.service
    
     [Service]
     EnvironmentFile=/etc/etcd.env
     Type=notify
     Restart=always
     RestartSec=5s
     LimitNOFILE=40000
     TimeoutStartSec=0
    
     ExecStart=/usr/local/bin/etcd --name <name> --data-dir /var/lib/etcd --listen-client-urls http://localhost:2379 --advertise-client-urls http://localhost:2379 --listen-peer-urls http://localhost:2380 --initial-advertise-peer-urls http://localhost:2380 --cert-file=/etc/kubernetes/pki/etcd/server.pem --key-file=/etc/kubernetes/pki/etcd/server-key.pem --client-cert-auth --trusted-ca-file=/etc/kubernetes/pki/etcd/ca.pem --peer-cert-file=/etc/kubernetes/pki/etcd/peer.pem --peer-key-file=/etc/kubernetes/pki/etcd/peer-key.pem --peer-client-cert-auth --peer-trusted-ca-file=/etc/kubernetes/pki/etcd/ca.pem --initial-cluster <etcd0>=https://<etcd0-ip-address>:2380,<etcd1>=https://<etcd1-ip-address>:2380,<etcd2>=https://<etcd2-ip-address>:2380 --initial-cluster-token my-etcd-token --initial-cluster-state new
    
     [Install]
     WantedBy=multi-user.target
     EOF

    Make sure you replace <etcd0-ip-address>, <etcd1-ip-address> and <etcd2-ip-address> with the appropriate IPv4 addresses. Replace <name> with the name of this etcd member. Modify the values of --listen-client-urls, --advertise-client-urls, --listen-peer-urls and --initial-advertise-peer-urls if needed. Replace <etcd0>, <etcd1> and <etcd2> with real hostnames of each machine. These machines must be able to reach every other using DNS or make sure that records are added to /etc/hosts.

  4. Finally, launch etcd:

     systemctl daemon-reload
     systemctl start etcd
  5. Check that it launched successfully:

     systemctl status etcd

Note: This is only supported on nodes that have the all dependencies for the kubelet installed. If you are hosting etcd on the master nodes, this has already been set up. If you are hosting etcd on dedicated nodes, you should either use systemd or run the installation guide on each dedicated etcd machine.

Run the following to generate the manifest file:

  cat >/etc/kubernetes/manifests/etcd.yaml <<EOF
  apiVersion: v1
  kind: Pod
  metadata:
    labels:
      component: etcd
      tier: control-plane
    name: <name>
    namespace: kube-system
  spec:
    containers:
    - command:
      - etcd --name <name> 
      - --data-dir /var/lib/etcd 
      - --listen-client-urls http://localhost:2379 
      - --advertise-client-urls http://localhost:2379 
      - --listen-peer-urls http://localhost:2380 
      - --initial-advertise-peer-urls http://localhost:2380 
      - --cert-file=/certs/server.pem 
      - --key-file=/certs/server-key.pem 
      - --client-cert-auth 
      - --trusted-ca-file=/certs/ca.pem 
      - --peer-cert-file=/certs/peer.pem 
      - --peer-key-file=/certs/peer-key.pem 
      - --peer-client-cert-auth 
      - --peer-trusted-ca-file=/certs/ca.pem 
      - --initial-cluster etcd0=https://<etcd0-ip-address>:2380,etcd1=https://<etcd1-ip-address>:2380,etcd2=https://<etcd2-ip-address>:2380 
      - --initial-cluster-token my-etcd-token 
      - --initial-cluster-state new
      image: k8s.gcr.io/etcd-amd64:3.1.10
      livenessProbe:
        httpGet:
          path: /health
          port: 2379
          scheme: HTTP
        initialDelaySeconds: 15
        timeoutSeconds: 15
      name: etcd
      env:
      - name: PUBLIC_IP
        valueFrom:
          fieldRef:
          fieldPath: status.hostIP
      - name: PRIVATE_IP
        valueFrom:
          fieldRef:
            fieldPath: status.podIP
      - name: PEER_NAME
        valueFrom:
          fieldRef:
            fieldPath: metadata.name
      volumeMounts:
      - mountPath: /var/lib/etcd
        name: etcd
      - mountPath: /certs
        name: certs
  hostNetwork: true
  volumes:
  - hostPath:
      path: /var/lib/etcd
      type: DirectoryOrCreate
    name: etcd
  - hostPath:
      path: /etc/kubernetes/pki/etcd
    name: certs
  EOF

Make sure you replace: * <name> with the name of the node you’re running on (e.g. etcd0, etcd1 or etcd2) * <etcd0-ip-address>, <etcd1-ip-address> and <etcd2-ip-address> with the public IPv4s of the other machines that host etcd.

Please select one of the tabs to see installation instructions for the respective way to set up a virtual IP.

Some examples of cloud provider solutions are:

You will need to ensure that the load balancer routes to just master0 on port 6443. This is because kubeadm will perform health checks using the load balancer IP. Since master0 is set up individually first, the other masters will not have running apiservers, which will result in kubeadm hanging indefinitely.

If possible, use a smart load balancing algorithm like “least connections”, and use health checks so unhealthy nodes can be removed from circulation. Most providers will provide these features.

In an on-site environment there may not be a physical load balancer available. Instead, a virtual IP pointing to a healthy master node can be used. There are a number of solutions for this including keepalived, Pacemaker and probably many others, some with and some without load balancing.

As an example we outline a simple setup based on keepalived. Depending on environment and requirements people may prefer different solutions. The configuration shown here provides an active/passive failover without load balancing. If required, load balancing can by added quite easily by setting up HAProxy, NGINX or similar on the master nodes (not covered in this guide).

  1. Install keepalived, e.g. using your distribution’s package manager. The configuration shown here works with version 1.3.5 but is expected to work with may other versions. Make sure to have it enabled (chkconfig, systemd, …) so that it starts automatically when the respective node comes up.

  2. Create the following configuration file /etc/keepalived/keepalived.conf on all master nodes:

     ! Configuration File for keepalived
     global_defs {
      router_id LVS_DEVEL
     }
    
     vrrp_script check_apiserver {
      script "/etc/keepalived/check_apiserver.sh"
      interval 3
      weight -2
      fall 10
      rise 2
     }
    
     vrrp_instance VI_1 {
        state <STATE>
        interface <INTERFACE>
        virtual_router_id 51
        priority <PRIORITY>
        authentication {
            auth_type PASS
            auth_pass 4be37dc3b4c90194d1600c483e10ad1d
        }
        virtual_ipaddress {
            <VIRTUAL-IP>
        }
        track_script {
            check_apiserver
        }
     }

    In the section vrrp_instance VI_1, change few lines depending on your setup:

    • state is either MASTER (on the first master nodes) or BACKUP (the other master nodes).
    • interface is the name of an existing public interface to bind the virtual IP to (usually the primary interface).
    • priority should be higher for the first master node, e.g. 101, and lower for the others, e.g. 100.
    • auth_pass use any random string here.
    • virtual_ipaddresses should contain the virtual IP for the master nodes.
  3. Install the following health check script to /etc/keepalived/check_apiserver.sh on all master nodes:

     #!/bin/sh
    
     errorExit() {
        echo "*** $*" 1>&2
        exit 1
     }
    
     curl --silent --max-time 2 --insecure https://localhost:6443/ -o /dev/null || errorExit "Error GET https://localhost:6443/"
     if ip addr | grep -q <VIRTUAL-IP>; then
        curl --silent --max-time 2 --insecure https://<VIRTUAL-IP>:6443/ -o /dev/null || errorExit "Error GET https://<VIRTUAL-IP>:6443/"
     fi

    Replace the <VIRTUAL-IP> by your chosen virtual IP.

  4. Restart keepalived. While no Kubernetes services are up yet it will log health check fails on all master nodes. This will stop as soon as the first master node has been bootstrapped.

Acquire etcd certs

Only follow this step if your etcd is hosted on dedicated nodes (Option 1). If you are hosting etcd on the masters (Option 2), you can skip this step since you’ve already generated the etcd certificates on the masters.

  1. Generate SSH keys for each of the master nodes by following the steps in the create ssh access section. After doing this, each master will have an SSH key in ~/.ssh/id_rsa.pub and an entry in etcd0’s ~/.ssh/authorized_keys file.

  2. Run the following:

     mkdir -p /etc/kubernetes/pki/etcd
     scp root@<etcd0-ip-address>:/etc/kubernetes/pki/etcd/ca.pem /etc/kubernetes/pki/etcd
     scp root@<etcd0-ip-address>:/etc/kubernetes/pki/etcd/client.pem /etc/kubernetes/pki/etcd
     scp root@<etcd0-ip-address>:/etc/kubernetes/pki/etcd/client-key.pem /etc/kubernetes/pki/etcd

Run kubeadm init on master0

  1. In order for kubeadm to run, you first need to write a configuration file:
  cat >config.yaml <<EOF
  apiVersion: kubeadm.k8s.io/v1alpha1
  kind: MasterConfiguration
  api:
    advertiseAddress: <virtual-ip>
    controlPlaneEndpoint: <virtual-ip>
  etcd:
    endpoints:
    - https://<etcd0-ip-address>:2379
    - https://<etcd1-ip-address>:2379
    - https://<etcd2-ip-address>:2379
    caFile: /etc/kubernetes/pki/etcd/ca.pem
    certFile: /etc/kubernetes/pki/etcd/client.pem
    keyFile: /etc/kubernetes/pki/etcd/client-key.pem
  networking:
    podSubnet: <podCIDR>
  apiServerCertSANs:
  - <virtual-ip>
  - <private-ip>
  apiServerExtraArgs:
    apiserver-count: "3"
  EOF

Ensure that the following placeholders are replaced:

Note: If you are using Kubernetes 1.9+, you can replace the apiserver-count: 3 extra argument with endpoint-reconciler-type: lease. For more information, see the documentation.
  1. When this is done, run kubeadm: bash kubeadm init --config=config.yaml

Run kubeadm init on master1 and master2

Before running kubeadm on the other masters, you need to first copy the K8s CA cert from master0. To do this, you have two options:

Option 1: Copy with scp

  1. Follow the steps in the create ssh access section, but instead of adding to etcd0’s authorized_keys file, add them to master0.
  2. Once you’ve done this, run:

     scp root@<master0-ip-address>:/etc/kubernetes/pki/* /etc/kubernetes/pki
     rm /etc/kubernetes/pki/apiserver*

Option 2: Copy paste

Copy the contents of /etc/kubernetes/pki/ca.crt, /etc/kubernetes/pki/ca.key, /etc/kubernetes/pki/sa.key and /etc/kubernetes/pki/sa.pub and create these files manually on master1 and master2.

When this is done, you can follow the previous step to install the control plane with kubeadm.

Add master1 and master2 to load balancer

Once kubeadm has provisioned the other masters, you can add them to the load balancer pool.

Install CNI network

Follow the instructions here to install the pod network. Make sure this corresponds to whichever pod CIDR you provided in the master configuration file.

Install workers

Next provision and set up the worker nodes. To do this, you will need to provision at least 3 Virtual Machines.

  1. To configure the worker nodes, follow the same steps as non-HA workloads.

Configure workers

  1. Reconfigure kube-proxy to access kube-apiserver via the load balancer:

     kubectl get configmap -n kube-system kube-proxy -o yaml > kube-proxy-cm.yaml
     sed -i 's#server:.*#server: https://<masterLoadBalancerFQDN>:6443#g' kube-proxy-cm.yaml
     kubectl apply -f kube-proxy-cm.yaml --force
     # restart all kube-proxy pods to ensure that they load the new configmap
     kubectl delete pod -n kube-system -l k8s-app=kube-proxy
  2. Reconfigure the kubelet to access kube-apiserver via the load balancer:

     sudo sed -i 's#server:.*#server: https://<masterLoadBalancerFQDN>:6443#g' /etc/kubernetes/kubelet.conf
     sudo systemctl restart kubelet

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