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

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.

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:

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:

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:

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.