Note: If you have missed my previous articles on Docker and Kubernetes, you can find them here
Application deployment models evolution.
Getting started with Docker.
Docker file and images.
Publishing images to Docker Hub and re-using them
Docker- Find out what's going on
Docker Networking- Part 1
Docker Networking- Part 2
Docker Swarm-Multi-Host container Cluster
Docker Networking- Part 3 (Overlay Driver)
Introduction to Kubernetes
Test Drive and Install KubernetesKubernetes cluster can be setup on a single node with Minicube which could be used in development/test environments. Production deployments use a multi-node Kubernetes cluster. In the previous article, I showed you how to deploy a multinode Kubernetes cluster with Ubuntu hosts running Docker. In this article, let's look at some of the Kubernetes concepts and finally deploy a service in the multinode cluster.
Node
Node is a host with Docker (or another container runtime) installed. A node can be a Master or Slave (a.k.a Minion). When PoDs are deployed, they are spread across Nodes on the cluster to achieve optimum load balancing.
PoD
A PoD is the smallest unit of abstraction in Kubernetes. A single PoD can contain multiple containers that are part of the application. For a 3 tier application, a PoD could be made up of a webserver, application server, and DB server containers. On the other hand, PoDs can also contain a single container image. PoDs can be scaled with replica sets.
Replica Sets/Replication Controller
The replication controller ensures the required number of replicas of PoD is always running. If a PoD/node goes down, the replication controller deploys PoDs to satisfy the required number of replica sets.
Deployment
Deployment is a set of identical PoDs that are used to run replicas of an application/microservice in Kubernetes. Typically deployments are used in production and can be used to perform hitless updates to the application.
Kubernetes Networking
Unlike Docker Swarm, Kubernetes does not have a default network and expects users to setup a network. Some of the requirements of the Kubernetes network are :
All containers within a PoD should be able to communicate with one another (Without NAT).
Containers should be able to communicate with Nodes and vice versa (without NAT).
Services running in PoD should be exposed to the outside world.
Fortunately, there are many Kubernetes Networking solutions. Some of them are
Cisco ACI
Cilium
Flannel
Calico
VMWare-NSX T
Look at https://kubernetes.io/docs/concepts/cluster-administration/networking/ for all the options out there.
Let's get started and setup a multinode cluster
Installing Kubernetes, Docker on Master and worker nodes
1. Disable swapfile in /etc/fstab by commenting it out and turn off swap.
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point> <type> <options> <dump> <pass>
# / was on /dev/sda1 during installation
UUID=74665848-fc50-4e30-bdcc-5ad47c295ecd / ext4 errors=remount-ro 0 1
#/swapfile none swap sw 0 0root@sathish-vm2:~# swapoff -a2. Install Kubernetes
root@sathish-vm2:~# apt-get update && sudo apt-get install -y apt-transport-https curlroot@sathish-vm2:~# curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key add -root@sathish-vm2:~# cat <<EOF | sudo tee /etc/apt/sources.list.d/kubernetes.list
deb https://apt.kubernetes.io/ kubernetes-xenial main
EOFroot@sathish-vm2:~# apt-get updateroot@sathish-vm2:~# apt-get install -y kubelet kubeadm kubectlroot@sathish-vm2:~# apt-mark hold kubelet kubeadm kubectl3. Install Docker (Ref: https://docs.docker.com/engine/install/ubuntu/)
root@sathish-vm2:~# apt-get install apt-transport-https ca-certificates curl gnupg lsb-release
root@sathish-vm2:~# curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg
gpg: WARNING: unsafe ownership on homedir '/home/extreme/.gnupg'
root@sathish-vm2:~# echo \
> "deb [arch=amd64 signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu \
> $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
root@sathish-vm2:~# apt-get update
root@sathish-vm2:~# apt-get install docker-ce docker-ce-cli containerd.ioInitialize master node
root@sathish-vm2:~# kubeadm init --pod-network-cidr=10.244.0.0/16
……………………………………
kubeadm join 10.127.13.203:6443 --token 1hgoov.dbks7wnix14rnad3 \
--discovery-token-ca-cert-hash sha256:bcb73f5f258621b27a53f5cdc8e3d49bf6a6a499ccfb972caa883e86f1e46c24Create .kubeconfig on master node
sathish@sathish-vm2:~$ mkdir -p $HOME/.kube
sathish@sathish-vm2:~$ sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
[sudo] password for extreme:
Sorry, try again.
[sudo] password for extreme:
sathish@sathish-vm2:~$Adding worker node to cluster
Use the join URL provided by kubeadm init to join the cluster
root@sathish-vm1:~# kubeadm join 10.127.13.203:6443 --token 1hgoov.dbks7wnix14rnad3 \
> --discovery-token-ca-cert-hash sha256:bcb73f5f258621b27a53f5cdc8e3d49bf6a6a499ccfb972caa883e86f1e46c24
………………………
root@sathish-vm2:~# kubectl get nodes
NAME STATUS ROLES AGE VERSION
kubemaster NotReady control-plane,master 13m v1.21.2
kubeworker NotReady <none> 41s v1.21.2Note: The nodes are in “Not Ready” state as we have not installed a networking plugin required for CNI (Container Network Interface).
Installing container network plugin (flannel)
root@sathish-vm2:~# sysctl net.bridge.bridge-nf-call-iptables=1
net.bridge.bridge-nf-call-iptables = 1kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.ymlCheck the nodes again
root@sathish-vm2:~# kubectl get nodes
NAME STATUS ROLES AGE VERSION
kubemaster Ready control-plane,master 18m v1.21.2
kubeworker Ready <none> 5m51s v1.21.2Removing Taint on Master node
By default, scheduling of PODs is disabled on the master node. This is achieved using a “NoScheduleTaint”. This should be removed to enable Kubernetes to schedule workloads on master node.
root@sathish-vm2:~# kubectl describe nodes | grep Taint
Taints: node-role.kubernetes.io/master:NoSchedule
Taints: <none>
root@sathish-vm2:~# kubectl taint node kubemaster node-role.kubernetes.io/master:NoSchedule-
node/kubemaster untainted
root@sathish-vm2:~# kubectl describe nodes | grep Taint
Taints: <none>
Taints: <none>
Verifying install by deploying various objectsCreating and verifying k8 objects
Create and verify POD
root@sathish-vm2:~# kubectl run nginx --image=nginx:alpine
root@sathish-vm2:~# kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx 1/1 Running 0 100s 10.244.1.4 kubeworker <none> <none>Create ,Verify and scale Deployment
root@sathish-vm2:~# kubectl create deployment mynginx --image=nginx --replicas=2
deployment.apps/mynginx created
root@sathish-vm2:~# kubectl get deployment
NAME READY UP-TO-DATE AVAILABLE AGE
mynginx 1/2 2 1 16s
root@sathish-vm2:~# kubectl get rs
NAME DESIRED CURRENT READY AGE
mynginx-5b686ccd46 2 2 2 79s
root@sathish-vm2:~# kubectl get pods
NAME READY STATUS RESTARTS AGE
mynginx-5b686ccd46-5bmtz 1/1 Running 0 82s
mynginx-5b686ccd46-prqtr 1/1 Running 0 82s
scaling mygnix
root@sathish-vm2:~# kubectl scale deployment mynginx --replicas=5
deployment.apps/mynginx scaled
root@sathish-vm2:~# kubectl get rs
NAME DESIRED CURRENT READY AGE
mynginx-5b686ccd46 5 5 2 2m20sHope this was informative. That's all for today folks.
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