Get insight into a Linux machine using Cockpit

Cockpit is an interactive Linux server admin interface. You can use it to monitor/ manage a Linux node through a web browser.

Install Cockpit on the Linux machine

yum install cockpit -y

systemctl start cockpit

systemctl enable --now cockpit.socket

Kubernetes 101 - Part2 - Basic operations

In this article, I will walk you through basic kubectl commands for working with K8s clusters.

kubectl cluster-info

kubectl version --short

kubectl get namespaces

kubectl get nodes -o wide

kubectl get pods -o wide --all-namespaces

kubectl get pods --show-labels

kubectl get nodes --show-labels

Deploy a pod

Following is a sample yaml file for deploying a CentOS pod:

apiVersion: v1

kind: Pod

metadata:

 name: centos-pod

 labels:

  zone: test

  version: v1

spec:

 containers:

 - name: centos-pod

   image: centos:latest

   command: ["sleep"]

   args: ["1d"]

 nodeSelector:

    kubernetes.io/hostname: w2

To deploy the pod:

kubectl create -f centos-pod.yml

kubectl describe pod centos-pod

SSH into the pod:

kubectl exec -it centos-pod sh

kubectl delete pod centos-pod

Hope it was useful. Cheers!

Kubernetes 101 - Part1 - Create K8s cluster with kubeadm

Deploy 3 CentOS 7 VMs. One will be the master and the other two will be workers/ slaves.

Master is "m1" and workers are "w1" and "w2".

Plan IP address

192.168.105.100 - m1
192.168.105.101 - w1
192.168.105.102 - w2

Step1: on all 3 nodes

vi /etc/hosts

192.168.105.100 m1
192.168.105.101 w1
192.168.105.102 w2

Step2: on all 3 nodes

#Disable firewall

sudo firewall-cmd --state
sudo systemctl stop firewalld
sudo systemctl disable firewalld
sudo systemctl status firewalld

setenforce 0
sed -i --follow-symlinks 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/sysconfig/selinux

Step3: on all 3 nodes

#Configure iptables for Kubernetes
cat <<EOF > /etc/sysctl.d/k8s.conf
net.bridge.bridge-nf-call-ip6tables = 1
net.bridge.bridge-nf-call-iptables = 1
EOF
sysctl --system

Step4: on all 3 nodes

#Disable swap

swapoff -a
vi /etc/fstab (Edit fstab file and comment(#) swap partition)

reboot all 3 nodes

Step5: on all 3 nodes

#configure kubernetes repo

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

EOF

Step6: Install docker on all 3 nodes

yum install docker -y

Step7: on all 3 nodes

yum install -y kubeadm kubectl kubelet --disableexcludes=kubernetes

systemctl daemon-reload
systemctl restart docker && systemctl enable --now docker
systemctl restart kubelet && systemctl enable --now kubelet

Step8: on master

kubeadm init --pod-network-cidr 10.244.0.0/16

Step9: on master

$ mkdir -p $HOME/.kube

$ sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config

$ sudo chown $(id -u):$(id -g) $HOME/.kube/config

Step10: on master

kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml

Step11: on all worker nodes

Use the join token from master to join worker nodes to the K8s cluster.

Example:

kubeadm join 192.168.105.100:6443 --token 4j1cjv.gcj2hx9suq5akc7v \

--discovery-token-ca-cert-hash sha256:b2ead930d772d8af2e45ca8c86c3895b092484c10f8034e52f917e71dc4c3fea

Hope it was useful. Cheers!

References

Why K8s on VMs?

https://kubernetes.io/docs/setup/production-environment/tools/kubeadm/install-kubeadm/

Docker 101 - Part3 - Persisting data using volumes

In this article, I will explain how to use Docker volumes for persisting data generated by and used by containers with --mount flag. Volumes use the Docker area and it can be found under /var/lib/docker/volumes/ directory of the Docker host.

Example:

docker run -dit --name centos_volume_test --mount source=data_volume01,target=/datavol01 centos sleep 1800

The above command will run a CentOS container and mounts a volume at /datavol01 inside the container. It uses source /var/lib/docker/volumes/data_volume01. The below screenshot shows the necessary steps to verify it.

Hope it was useful. Cheers!

Related posts

Docker 101 - Part2 - Basic operations

Docker 101 - Part1 - Installation

References

https://docs.docker.com/storage/volumes/

https://docs.docker.com/storage/bind-mounts/

Docker 101 - Part1 - Installation

Enter cloud native! In this article, I will briefly explain how to build a virtual Docker host. Here I am installing Docker on a CentOS 7.4 virtual machine running on ESXi 6.5 which is part of a VMware vSAN cluster.

Prerequisites:

• Deploy a basic CentOS 7.4 VM
• Assign IP address and ensure the VM has internet connectivity
• You should have root creds

Installation:

• SSH to the CentOS VM as root
• yum check-update
• yum install -y yum-utils device-mapper-persistent-data lvm2
• yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
• yum install docker-ce
• systemctl start docker
• systemctl enable docker
• systemctl status docker

Verify version:

• docker version

Run your first container:

• docker run hello-world

Hope it was useful. Cheers! In the next part, I will explain basic Docker commands and operations.

Related posts

Docker 101 - Part2 - Basic operations

References

https://docs.docker.com/install/linux/docker-ce/centos/
https://phoenixnap.com/kb/how-to-install-docker-centos-7
https://linuxize.com/post/how-to-install-and-use-docker-on-centos-7/
https://www.digitalocean.com/community/tutorials/how-to-install-and-use-docker-on-centos-7