kubernetes

minikube

minikube start
--vm-driver='': Driver is one of: [virtualbox parallels vmwarefusion kvm2 vmware none] (defaults to auto-detect)

minikube service --url vote-app

concepts

docker: container, image, tags

kubernetes:

• nodes (formerly minions): machine (hardware or vm) units
• cluster: set of nodes
• pods: multiple containers, share one ip and volumes, run on same machine
• services: set of pods
• replication controllers: restart pods, load balancing, scaling
• replica set: replacement for replication controller, selector is required
• labels: key-value
• volumes
• secrets
• namespaces
• cluster: set of grouped nodes, balancing, fallback

components

master node, part of cluster, watches over nodes:

• api server: frontend
• etcd: key-value store
• scheduler: assigns containers to nodes
• controller: notice and respond to changes

worker node:

• container runtime: f.e. docker
• kubelet: runs on nodes, watches containers

rollout / deployment

kubectl create or kubectl run. deployments create their own replicasets.

deployment strategies:

• recreate: destroy and rebuild, downtime

• rolling update, default: each pod

• kubectl apply -f <file>

• kubectl rollout undo deployment/myapp-deployment

• kubectl rollout status deployment/myapp-deployment

networking

• pods get ip adresses
• to prevent conflicts in the cluster need to install/configure s.th., not builtin

services

exposes port which forwards to several pods of same type.

• kinds
  • ClusterIP: default, exposes on a cluster-internal ip
  • NodePort: exposes publicly on each node at a static port (curl <nodeIP>:<nodePort>), includes ClusterIP service
  • LoadBalancer: connects w/ cloud provider's load balancer
• targetPort: on pod, what container provides, defaults to port
• port: on service, like virtual server inside node, required
• nodePort: on each node, 30.000-23.767, defaults to autogenerate
• clusterIP: to be identified inside cluster
• matches to pods via selector, clusterwide
• balancing: random w/ SessionAffinity

tools

kubeadm

used to setup kubernetes cluster.

kubectx

show and select contexts (clusters), f.e.

kubectx      # list all
kubectx foo  # switch to "foo"
kubectx -c   # show current
kubectx -h

kubens

show and select namespaces inside context.

kubens      # list all
kubens foo  # switch to "foo"
kubens -c   # show current
kubens -h

kubectl

kubectl config use-context docker-for-desktop
kubectl cluster-info
kubectl get nodes
# create pod, deploy image
kubectl run nginx --image=nginx
kubectl get pods
kubectl get pods -o wide
kubectl get pods -o yaml
kubectl describe pods
kubectl get deployments
kubectl delete deployment nginx
kubectl get all

yaml

• apiVersion: v1 for pods and services, app/v1 for replicasets and deployments

• kind

• metadata:name: cascades to subcomponents, that is pods will have name of replicaset or deployment, don't need to be unique, but probably a good idea

• metadata:labels: used for selectors and custom categorizing

• kubectl create -f <file>

• kubectl create -f . processes all files in dir

• kubectl replace -f <file> disruptive update

• kubectl apply -f <file> create or in-place update

• kubectl diff -f <file> show what apply would do

namespaces

• kube-system
• kube-public
• default: playground, don't use on real-life cluster
• connect to service "db" via connect("db"), from other namespave via connect("db.<namespace>.svc.cluster.local")
• specify namespace via kubectl --namespace or via yaml as metadata:namespace
• kubectl create namespace myapp-dev or via yaml
• kubectl config set-context $(kubectl config current-context) --namespace=myapp-dev
• kubectl get pods --all-namespaces
• ResourceQuota puts limits on namespaces

unsorted

• Ingress does what Route does in okd
• Helm is a thing
• containerPort in pod def, does it obsolete service port defs?