Kubernetes Notes

Your Kubernetes control-plane has initialized successfully!

* Kubeadm init to start the cluster off.

Success:

#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/

Then you can join any number of worker nodes by running the following on each as root:

kubeadm join 192.168.1.160:6443 --token bt5jqu.92na40x473dukgdb \
    --discovery-token-ca-cert-hash sha256:2c2962c2f31519a5946064a1bbc0671367d4dd9630715ecfb2c71dfd1d4eed28

Other notes:

• Swap must be turned off (Caught in kubeadm preflight)
• Selinux must be off and disabled
• Ports:

What is a pod?

• Defines one or more containers
  • How they run
  • Resources needed
• Kubernetes manages pods, NOT containers
• Most applications use one application per pod
• Containers in same pod talk via localhost

Multi container pods

• Containers in same pod scaled identically, can be an issue for apps like database.
• Only group tightly coupled services into a pod.
• initContainers may contain software, passwords or secrets only used for startup
  • May allow you to use other images without changes
  • Example: Static site generator feeding output to volume which is then mounted at document root for web server.
  • Delay start of rest of service until they are complete.

Networking:

• NetworkPolicy defines external access to pods within the cube
  • CIDR Blocks
  • App labels
  • Ports
• Blank policies block everything
• Policy of {} allows all
• Network Docs

Controllers:

• Abstraction layer on top of pods
• They create and manage pods

Services:

Secrets & ConfgMaps:

• Secrets base64 encoded in config, viewable as plain text in pod
• Use RBAC to protect
• ConfgMaps primarily for config data

Volumes:

• Typically creed to be created before use
• RO or RW
• Plain Volumes are deleted with pod, underlying storage may remain
• Volume Docs