Kubernetes

with the help of - https://www.redhat.com/sysadmin/podman-inside-kubernetes - https://www.howtoforge.com/how-to-setup-kubernetes-cluster-with-kubeadm-on-rocky-linux/ mnemonic for a test cluster with - 1 controller - 3 workers - Rocky Linux 9 - podman not docker, because it's superiour - netavark - containerd - IPv6 centered

Basics - Object types

• Pods A container or a logical group of containers
• Replica Sets How many pods shall there be?
• Services A service within the kubernetes cluster
• Volumes Volumes for pods
• Name Spaces logical groups for DNS and privilege separation
• ConfigMaps and Secrets environment variables and secrets
• Stateful Sets for statefull applications
• Daemon Sets Kubernetes Scheduler???

Basics - Commands

• change namespace (here: backend) kubectl config set-context --current --namespace=backend

General

• Setup DNS records for your nodes or make entries in /etc/hosts
• Set hostnames for your nodes, mine will be
• pod-ctrl-3
• pod-worker-4
• pod-worker-5
• pod-worker-6
• example command hostnamectl hostname pod-ctrl-3 --static
• set selinux to permissive

  sudo setenforce 0
  sudo sed -i 's/^SELINUX=enforcing$/SELINUX=permissive/' /etc/selinux/config
  

• Kernel modules and parameters

  cat <<EOF | sudo tee /etc/sysctl.d/k8s.conf
  net.bridge.bridge-nf-call-iptables  = 1
  net.bridge.bridge-nf-call-ip6tables = 1
  net.ipv4.ip_forward                 = 1
  net.ipv6.conf.all.forwarding        = 1
  EOF
  sudo sysctl --system
  cat <<EOF | sudo tee /etc/modules-load.d/k8s.conf
  overlay
  br_netfilter
  EOF
  sudo modprobe overlay
  sudo modprobe br_netfilter
  

• Installing

  dnf -y install dnf-utils
  sudo yum-config-manager \
      --add-repo \
      https://download.docker.com/linux/centos/docker-ce.repo
  sudo dnf repolist
  sudo dnf makecache
  sudo dnf -y install containerd.io
  

• Configuring

  mv /etc/containerd/config.toml /etc/containerd/config.toml.original
  sudo containerd config default > /etc/containerd/config.toml
  sudo vim /etc/containerd/config.toml
  

• Replace SystemdCgroup = false with SystemdCgroup = true
• Start containerd with sudo systemctl enable --now containerd
• Install kube admin packages

  cat <<EOF | sudo tee /etc/yum.repos.d/kubernetes.repo
  [kubernetes]
  name=Kubernetes
  baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-\$basearch
  enabled=1
  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=kubelet kubeadm kubectl
  EOF
  sudo dnf repolist
  sudo dnf makecache
  sudo dnf install kubelet kubeadm kubectl --disableexcludes=kubernetes
  sudo systemctl enable --now kubelet
  

• Initialize

  sudo kubeadm config images pull
  

Controller (Master) only

• Setup firewall

  sudo firewall-cmd --add-port=6443/tcp --permanent
  sudo firewall-cmd --add-port=2379-2380/tcp --permanent
  sudo firewall-cmd --add-port=10250/tcp --permanent
  sudo firewall-cmd --add-port=10259/tcp --permanent
  sudo firewall-cmd --add-port=10257/tcp --permanent
  sudo firewall-cmd --reload
  sudo firewall-cmd --list-all
  

Workers only

• swapoff -a
• sudo sed -i '/ swap / s/^\(.*\)$/#\1/g' /etc/fstab
• Setup firewall

  sudo firewall-cmd --add-port=10250/tcp --permanent
  sudo firewall-cmd --add-port=30000-32767/tcp --permanent
  sudo firewall-cmd --reload
  sudo firewall-cmd --list-all