How To Install Kubernetes on CentOS 7 / Ubuntu 18.04 / 16.04 & Debian 9

Kubernetes is an open-source Production-Grade container orchestration tool that helps to automate deploying, scaling, managing containerized applications. Google initially designed Kubernetes and now maintained by the Cloud Native Computing Foundation.

You can call Kubernetes is a cluster manager for Docker, and it provides almost same functionalities that of Docker Swarm. With Kubernetes, you can deploy any number of container replicas onto a node cluster, and Kubernetes will handle remainings (where to bring up containers) for you.

We can run Kubernetes in local-machine using below methods,

1. MinKube – A single node Kubernetes cluster for development and testing.
2. Kubeadm-dind (Kuberadm) – A multi-node Kubernetes cluster

You can read all the methods here.

Here, we will deploy a multi-node Kubernetes cluster using the kubeadm. In this multi-node setup, we will have one master node and multiple worker nodes (minions).

Components

Master Node

kube-API server: It is an API server, runs on the master node that exposes Kubernetes API
etcd: A key store that stores Kubenetes cluster data
kube-scheduler: It is a scheduler that runs on the master node which monitors newly created pods and runs those pods on select nodes depends on resource availability.
kube-controller-manager: It is a control manager that runs on the manager who is responsible for monitoring nodes and maintaining pods replication.
cloud-controller-manager: A cloud control manager that interact with underlying cloud providers (Ex: DigitalOcean, Rancher, etc..).

Worker Nodes

kubelet: It runs on all worker nodes and handles tasks like starting pods and containers.
kube-proxy: It is a Kubernetes network proxy that forwards TCP/UDP incoming requests to backend container.
Container Runtime: It is container software (Docker)

Environment

Node	Hostname	IP Address	OS	CPU	RAM
Master Node	master.itzgeek.local	192.168.1.10	CentOS 7 / RHEL 7	2	2GB
Minion Node 1	node1.itzgeek.local	192.168.1.20	Ubuntu 18.04 / 16.04	2	2GB
Minion Node 2	node2.itzgeek.local	192.168.1.30	Debian 9	2	2GB

You must disable swap for Kubernetes to work properly

Here, I am using a mixed environment for this demo. But, I request you use the similar operating system only for ease troubleshooting.

Prerequisites

Become the root user.

su -

OR

sudo su -

Set Hostname

Set unique hostname for all your nodes. Example:

hostnamectl set-hostname master.itzgeek.local

Make a host entry or DNS record to resolve hostname for all nodes.

vi /etc/hosts

Entry:

192.168.1.10 master.itzgeek.local master  192.168.1.20 node1.itzgeek.local node1  192.168.1.30 node2.itzgeek.local node2

Firewall

Configure Firewall for Kubernetes to work correctly.

ON MASTER NODE

FirwallD:

firewall-cmd --permanent --add-port=6443/tcp  firewall-cmd --permanent --add-port=2379-2380/tcp  firewall-cmd --permanent --add-port=10250/tcp  firewall-cmd --permanent --add-port=10251/tcp  firewall-cmd --permanent --add-port=10252/tcp  firewall-cmd --permanent --add-port=10255/tcp  firewall-cmd --reload

UFW:

ufw allow 6443/tcp  ufw allow 2379tcp  ufw allow 2380/tcp  ufw allow 10250/tcp  ufw allow 10251/tcp  ufw allow 10252/tcp  ufw allow 10255/tcp  ufw reload

ON WORKER NODES

FirwallD:

firewall-cmd --permanent --add-port=10251/tcp  firewall-cmd --permanent --add-port=10255/tcp  firewall-cmd --reload

UFW:

ufw allow 10251/tcp  ufw allow 10255/tcp  ufw reload

SELinux

Consider disabling SELinux on CentOS 7 / RHEL 7 nodes.

setenforce 0    sed -i 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/selinux/config

Kernel Settings

In RHEL 7 /CentOS 7, set net.bridge.bridge-nf-call-iptables to 1 in your sysctl config.

cat <<EOF > /etc/sysctl.d/k8s.conf  net.bridge.bridge-nf-call-ip6tables = 1  net.bridge.bridge-nf-call-iptables = 1  EOF  sysctl -p

Install Docker

Install Docker on all of your nodes (Master and Minions). Docker version v18.06 is recommended, but v1.11,  v1.12, v1.13 and 17.03 also work well with Kubernetes.

CentOS 7 / RHEL 7

### Install Docker from CentOS/RHEL repository ###    yum install -y docker  systemctl enable docker   systemctl start docker    OR    ### Install Docker CE 18.06 from Docker's CentOS repositories ###    # Install Prerequisites   yum install -y yum-utils device-mapper-persistent-data lvm2    # Add Docker repository   yum-config-manager       --add-repo       https://download.docker.com/linux/centos/docker-ce.repo    # Install Docker  yum update  yum install -y docker-ce-18.06.1.ce    # Create Docker Directory   mkdir /etc/docker    # Setup Docker Daemon  cat > /etc/docker/daemon.json <<EOF  {  "exec-opts": ["native.cgroupdriver=systemd"],  "log-driver": "json-file",  "log-opts": {  "max-size": "100m"  },  "storage-driver": "overlay2",  "storage-opts": [  "overlay2.override_kernel_check=true"  ]  }  EOF    mkdir -p /etc/systemd/system/docker.service.d    # Restart Docker Daemon  systemctl daemon-reload  systemctl restart docker  systemctl enable docker

Ubuntu 18.04 / Ubuntu 16.04

### Install Docker from Ubuntu's repositories ###    apt-get update  apt-get install -y docker.io    OR    ### Install Docker CE 18.06 from Docker's repositories for Ubuntu  ###    # Install Prerequisites  apt-get update  apt-get install -y apt-transport-https ca-certificates curl software-properties-common    # Download GPG Key  curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add -    # Add Docker's Repository   add-apt-repository      "deb [arch=amd64] https://download.docker.com/linux/ubuntu      $(lsb_release -cs)      stable"    # Install Docker  apt-get update  apt-get install -y docker-ce=18.06.0~ce~3-0~ubuntu    # Setup Daemon  cat > /etc/docker/daemon.json <<EOF  {  "exec-opts": ["native.cgroupdriver=systemd"],  "log-driver": "json-file",  "log-opts": {  "max-size": "100m"  },  "storage-driver": "overlay2"  }  EOF    mkdir -p /etc/systemd/system/docker.service.d    # Restart Docker Daemon  systemctl daemon-reload  systemctl restart docker

Debian 9

### Install Docker from Debian's repositories ###    apt-get update  apt-get install -y docker.io    OR    ### Install Docker CE 18.06 from Docker's repositories for Debian ###    # Install Prerequisites  apt-get update  apt-get install -y apt-transport-https ca-certificates curl software-properties-common    # Download GPG Key   curl -fsSL https://download.docker.com/linux/debian/gpg | apt-key add -    # Add Docker's Repository  add-apt-repository      "deb [arch=amd64] https://download.docker.com/linux/debian      $(lsb_release -cs)      stable"    # Install Docker  apt-get update  apt-get install -y docker-ce=18.06.0~ce~3-0~debian    # Setup Daemon  cat > /etc/docker/daemon.json <<EOF  {  "exec-opts": ["native.cgroupdriver=systemd"],  "log-driver": "json-file",  "log-opts": {  "max-size": "100m"  },  "storage-driver": "overlay2"  }  EOF    mkdir -p /etc/systemd/system/docker.service.d    # Restart Docker Daemon  systemctl daemon-reload  systemctl restart docker  

Configure Kubernetes Repository

Kubernetes packages are not available in OS repositories, so you need to follow the below steps to configure its repository on all your nodes.

### CentOS 7 / RHEL 7 ###    cat <<EOF > /etc/yum.repos.d/kubernetes.repo  [kubernetes]  name=Kubernetes  baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64  enabled=1  gpgcheck=1  repo_gpgcheck=1  gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg  exclude=kube*  EOF    ### Ubuntu 18.04 / 16.05 & Debian 9 ###    apt-get update  apt-get install -y curl apt-transport-https  curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | apt-key add -  echo "deb http://apt.kubernetes.io/ kubernetes-xenial main" | sudo tee /etc/apt/sources.list.d/kubernetes.list  

Install kubeadm, kubelet and kubectl

On all of your nodes, run the following commands to install required packages.

kubeadm: the command to create the cluster.

kubelet: Runs on all of the machines in your cluster and does things like starting pods and containers.

kubectl: the command line utility to manage your cluster.

### CentOS 7 / RHEL 7 ###    yum install -y kubelet kubeadm kubectl --disableexcludes=kubernetes  systemctl enable kubelet   systemctl start kubelet  ### Ubuntu 16.04 / Debian 9 ###    apt-get update  apt-get install -y kubelet kubeadm kubectl

Initialize Kubernetes Master

On the Master node, execute the kubeadm init command in the terminal to initialize the cluster.

Depending upon the network add-on you use, you may need to set the --pod-network-cidr to a specific value. Here, I am using Wave pod network which doesn’t require any extra arguments.

kubeadm init

Output:

[init] Using Kubernetes version: v1.13.0  [preflight] Running pre-flight checks          [WARNING Firewalld]: firewalld is active, please ensure ports [6443 10250] are open or your cluster may not function correctly  [preflight] Pulling images required for setting up a Kubernetes cluster  [preflight] This might take a minute or two, depending on the speed of your internet connection  [preflight] You can also perform this action in beforehand using 'kubeadm config images pull'    [kubelet-start] Writing kubelet environment file with flags to file "/var/lib/kubelet/kubeadm-flags.env"  [kubelet-start] Writing kubelet configuration to file "/var/lib/kubelet/config.yaml"  [kubelet-start] Activating the kubelet service  [certs] Using certificateDir folder "/etc/kubernetes/pki"  [certs] Generating "ca" certificate and key  [certs] Generating "apiserver-kubelet-client" certificate and key    .      .      .  .      .      .  .      .      .    [bootstraptoken] configured RBAC rules to allow certificate rotation for all node client certificates in the cluster  [bootstraptoken] creating the "cluster-info" ConfigMap in the "kube-public" namespace  [addons] Applied essential addon: CoreDNS  [addons] Applied essential addon: kube-proxy    Your Kubernetes master has initialized successfully!    To start using your cluster, you need to run the following as a regular user:      mkdir -p $HOME/.kube    sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config    sudo chown $(id -u):$(id -g) $HOME/.kube/config    You should now deploy a pod network to the cluster.  Run "kubectl apply -f [podnetwork].yaml" with one of the options listed at:    https://kubernetes.io/docs/concepts/cluster-administration/addons/    You can now join any number of machines by running the following on each node  as root:      kubeadm join 192.168.1.10:6443 --token d1dyaj.31zxywbg93s1ywjy --discovery-token-ca-cert-hash sha256:71a91721595fde66b6382908d801266602a14de8e16bdb7a3cede21509427009  

Manage Cluster

Run these commands in the terminal to manage and work on the cluster as a regular user.

mkdir -p $HOME/.kube  sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config  sudo chown $(id -u):$(id -g) $HOME/.kube/config

Run the kubectl get pods –all-namespaces command to check the status of the cluster.

kubectl get pods --all-namespaces

Output:

Install Kubernetes on CentOS 7 – Cluster Status

You can see that coredns pod is in pending state and the status should change once you install pod network.

Setup Pod Network

We need to set up a pod network add-on on the cluster so that pods can communicate with each other. There are several projects provide Kubernetes pod networks namely, calico, canal, flannel, etc.

Here, we will use Wave pod network for this demo.

export kubever=$(kubectl version | base64 | tr -d 'n')  kubectl apply -f "https://cloud.weave.works/k8s/net?k8s-version=$kubever"

Output:

serviceaccount/weave-net created  clusterrole.rbac.authorization.k8s.io/weave-net created  clusterrolebinding.rbac.authorization.k8s.io/weave-net created  role.rbac.authorization.k8s.io/weave-net created  rolebinding.rbac.authorization.k8s.io/weave-net created  daemonset.extensions/weave-net created  

Check the cluster status once again. The coredns pod should now be running state.

kubectl get pods --all-namespaces

Output:

Install Kubernetes on CentOS 7 – Cluster Status post installing Network Add-on

Join worker nodes to Kuberenete cluster

If you remember, there was token in the output of kubeadm init command for joining nodes. Use the token and join all of your worker nodes.

kubeadm join 192.168.1.10:6443 --token d1dyaj.31zxywbg93s1ywjy --discovery-token-ca-cert-hash sha256:71a91721595fde66b6382908d801266602a14de8e16bdb7a3cede21509427009

Output:

[preflight] Running pre-flight checks  [discovery] Trying to connect to API Server "192.168.1.10:6443"  [discovery] Created cluster-info discovery client, requesting info from "https://192.168.1.10:6443"  [discovery] Requesting info from "https://192.168.1.10:6443" again to validate TLS against the pinned public key  [discovery] Cluster info signature and contents are valid and TLS certificate validates against pinned roots, will use API Server "192.168.1.10:6443"  [discovery] Successfully established connection with API Server "192.168.1.10:6443"  [join] Reading configuration from the cluster...  [join] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -oyaml'  [kubelet] Downloading configuration for the kubelet from the "kubelet-config-1.13" ConfigMap in the kube-system namespace  [kubelet-start] Writing kubelet configuration to file "/var/lib/kubelet/config.yaml"  [kubelet-start] Writing kubelet environment file with flags to file "/var/lib/kubelet/kubeadm-flags.env"  [kubelet-start] Activating the kubelet service  [tlsbootstrap] Waiting for the kubelet to perform the TLS Bootstrap...  [patchnode] Uploading the CRI Socket information "/var/run/dockershim.sock" to the Node API object "node1.itzgeek.local" as an annotation    This node has joined the cluster:  * Certificate signing request was sent to apiserver and a response was received.  * The Kubelet was informed of the new secure connection details.    Run 'kubectl get nodes' on the master to see this node join the cluster.  

The above output confirms that the node has been successfully added to the cluster.

Now, check the worker nodes status on the master node using the following command.

kubectl get nodes

Output:

Install Kubernetes on CentOS 7 – Nodes List

You should see worker nodes are in ready state.

In our next article, we will deploy pods, services, and replication controllers in Kubernetes.

That’s All.

from https://www.itzgeek.com/how-tos/linux/centos-how-tos/how-to-install-kubernetes-on-centos-7-ubuntu-18-04-16-04-debian-9.html