Completek8s Classroomnotes 01/Aug/2023

Kubernetes the Hardway installation

• The state as of now is we are able to run the etcd from commandline as root user

/usr/local/bin/etcd \
  --name ip-172-31-51-202 \
  --cert-file=/etc/etcd/kubernetes.pem \
  --key-file=/etc/etcd/kubernetes-key.pem \
  --peer-cert-file=/etc/etcd/kubernetes.pem \
  --peer-key-file=/etc/etcd/kubernetes-key.pem \
  --trusted-ca-file=/etc/etcd/ca.pem \
  --peer-trusted-ca-file=/etc/etcd/ca.pem \
  --peer-client-cert-auth \
  --client-cert-auth \
  --initial-advertise-peer-urls https://172.31.51.202:2380 \
  --listen-peer-urls https://172.31.51.202:2380 \
  --listen-client-urls https://172.31.51.202:2379,https://127.0.0.1:2379 \
  --advertise-client-urls https://172.31.51.202:2379 \
  --initial-cluster-token etcd-cluster-0 \
  --initial-cluster controller-0=https://10.240.0.10:2380,controller-1=https://10.240.0.11:2380,controller-2=https://10.240.0.12:2380 \
  --initial-cluster-state new

• But running as service is not working out

[Unit]
Description=etcd
Documentation=https://github.com/coreos

[Service]
Type=notify
ExecStart=/usr/local/bin/etcd \
  --name ip-172-31-51-202 \
  --cert-file=/etc/etcd/kubernetes.pem \
  --key-file=/etc/etcd/kubernetes-key.pem \
  --peer-cert-file=/etc/etcd/kubernetes.pem \
  --peer-key-file=/etc/etcd/kubernetes-key.pem \
  --trusted-ca-file=/etc/etcd/ca.pem \
  --peer-trusted-ca-file=/etc/etcd/ca.pem \
  --peer-client-cert-auth \
  --client-cert-auth \
  --initial-advertise-peer-urls https://172.31.51.202:2380 \
  --listen-peer-urls https://172.31.51.202:2380 \
  --listen-client-urls https://172.31.51.202:2379,https://127.0.0.1:2379 \
  --advertise-client-urls https://172.31.51.202:2379 \
  --initial-cluster-token etcd-cluster-0 \
  --initial-cluster controller-0=https://10.240.0.10:2380,controller-1=https://10.240.0.11:2380,controller-2=https://10.240.0.12:2380 \
  --initial-cluster-state new
Restart=on-failure
RestartSec=5

[Install]
WantedBy=multi-user.target

Kubernetes Primitives – Pod

• The smallest unit of creation for
  • Hypervisor is Virtual Machine
  • Docker is Container
  • K8s is Pod
    
• Pod can have one or more container(s) in it.
• Recommended practice of k8s recommends running a microservice in a Pod and databases in different pods
• Scaling Application in k8s is increasing number of Pods not number of containers in a Pod
  
• Kubernetes maintains desired state
• For some of the explorations in terms of primitives
  • playground Refer Here
  • minikube
• Create a simple pod with any image

kubectl create nginx --image=nginx
# to  login into nginx
kubectl exec -it nginx -- /bin/bash
# install net-tools
apt update && apt install net-tools
ifconfig
# two network interfaces `lo` and `etho` (with pod ip)
exit

• Create an alpine pod with sleep 1d as argument with kubectl run imperative commands
• Refer Here for kubectl cheatsheet