Kubernetes Concepts

Turn key solutions:

• RedHat OpenShift
• Vultr
• Linode
• Google Kubernetes Engine
• AWS
• Digital Ocean

Some terms:

• kubectl - control tool
• kubeadm - setting up clusters
• kind - to run on local computer
• minikube - run single node cluster on your computer
• k3s - mini kubernetes from Rancher Labs

Pods:

• kind of like application specific logical hosts
• resources
  • shared storage volumes
  • networking with unique cluster IP
  • container info ( ports, image, etc. )

Nodes

• worker machine
• VM or physical
• multiple pods
• kublet
• container runtime

Service

• logical set of pods
• provides access to them
• type
  • ClusterIP (default)
    • setup internal IP within cluster
    • also load balances
  • NodePort
    • expose with NAT
    • also load balances
    • 30000 - 32767
  • LoadBalancer
    • create load balancer with external IP (NEEDS third party LB!!!!)
    • cloud only ?
  • ExternalName - setup a DNS name

More terms:

• Deployment - Used to create and update application instances.
• ReplicaSet - Pods can be run and failover within this.

• Labels and Selectors - You can categorize things with these.

• CRI - Container Runtime Interface

Container runtimes:

• containerd
• CRI-O
• Docker Engine
• Mirantis Container Runtime

Important tips:

• best to only have one cgroup manager
• use systemd as cgroup manager
• set this with docker: native.cgroupdriver=systemd
• cgroups v2 can be installed
• docker runs containerd

Windows containers?

Deployment tools:

• Kubespray
• kops
• kubeadm

Nodes

* pods
    * containers

Control plane

* kube-apiserver
* etcd - key store for cluster data
* kube-scheduler - assigns pods to nodes and probably more
* kube-controller-manager 
    * Node controller
    * Job controller
    * Endpoints controller
    * Service Account & Token controllers
* cloud-controller-manager - only in the cloud
    * Node controller
    * Route controller
    * Service controller

Node components:

• kubelet - makes sure containers in PodSpecs are running
• kube-proxy - manages network stuff for the node
• container runtime

Addons

• DNS ( Cluster DNS )
• Web UI ( Dashboard )
• Container Resource Monitoring
• Cluster-level Logging

API accessed with

• kubectl
• kubeadm
• REST
• API Objects: Pods, Namespaces, ConfigMaps, and Events

Objects:

• spec - what it should be
• status - what it currently is
• has name and UID

Object management:

• Imperative commands - adhoc commands ( good for dev )
• Imperative object configuration - objects defined in files ( good for prod ) WARN - could overwrite stuff
• Declarative object configuration - objects defined in files within a dir ( good for prod )

Namespaces

• isolation groups
• provide scoping
• good for teams and projects

kubectl get namespace

4 initial namespaces:

• default
• kube-system
• kube-public
• kube-node-lease

Terms to expand on:

• Labels and Selectors - these exist
• Annotations - these also exist
• Field Selectors - these exist too
• Finalizers - wait for condition before fully deleting, can block deletion
• Owners and Dependents - some objects own others

Field selector example:

kubectl get pods --field-selector status.phase=Running