Docker Kubernetes

Docker Kubernetes

• Kubernets is a popular container orchestrator
• Container Orchestration is something that makes many servers act like one.

What is the benifit of using orchestration?

• It automatically applies changes. (Is it the most important benefit??)
  • Servers + Change Rate = Benefit of orchestration.
• It enables for us to control lots of servers at once.

Advantages of Kubernetes

• a bit difficult(?) but more functional
• Clouds will deploy/manage Kubernetes for us
• Widest adoption and community
• Trendy

Terms

• Kubernetes: The whole orchestration system. Also called as K8s
• Kubectl: CLI to configure Kubernetes and manage apps
• Node: Single server in the Kubernetes cluster
• Kubelet: Kubernetes agent running on nodes(workers)
• Control Plane: Similar to Manager in Swarm but it also means group of masters
  • master node 들의 집합이라고 보면 될 듯!
• Pod : One or more containers running together on one Node
• Controller: For creating/updating pods and other objects
• Service: Network endpoint to connect to a pod
• etcd: Distributed storage system -> DB
  • 발음은 엣씨디..

About Service

ClusterIP

• cluster 내에서 사용되는 IP

NodePort

• 다른 노드 또는 외부에서 접근할 수 있는 IP

LoadBalancer

• cluster로 통하는 LB의 endpoint를 관리.
• Only availabel when infra provider gives us a LB (AWS’s ELB… etc..)

Node Structure

Master

• etcd
• API
• Scheduler
• Controller manager
• Core DNS

Node (worker)

• kublet (agent)
• kube-proxy : controls network

Local setup

• MicroK8s : ubuntu 버전으로 나왔지만 다른 OS에서도 잘 작동함.

1.

$ snap microk8s --classic --channel=1.18/stable

2.

$ microk8s.enable dns

참고: microk8s.xxx 명령어로 다양한 조작 가능!

Tips

alias kubectl=microk8s.kubectl 설정해놓는걸 추천`

kubectl 가동 방법

kubectl run

• kubectl run only create single pods.
  • ex) $ kubectl run <Pods name> --image <image name>

kubectl create

• creates replicaSet
  • ex) $ kubectl create <Deployment> <Pods> --image <image name>

kubectl apply

• yml 하고 같이 사용됨.
• create/update resources in a file.
  • kubectl apply -f myfile.yaml
• create/update a whole directory of yaml
  • kubectl apply -f myyaml/
• create/update from a URL
  • kubectl apply -f https://my.com/pod.yml
    • 이 커맨드는 시작 전에 curl 등으로 내용을 한 번 확인하고 실행하는걸 추천

YAML 구조

4 가지 요소는 무조건 포함해야함

• apiVersion
• kind
• metadata
• spec

Build YAML files

• kind: We can get a list of resources the cluster supports
  • kubectl api-resources 로 리소스 종류를 확인할 수 있음. Kind도!
• apiVersion: We can get the API versions the cluster supports
  • kubectl api-versions 로 확인 가능
• Tips: kind + apiVersion 은 세트로 생각할 것!
• metadata: only name is required
• spec: Where all the action is at!

Build YAML spec

• kubectl explain services --recursive We can get all the keys each kind supports
• kubectl explain services.spec
  • Spec에 관련된 정보만 얻을 수 있음
    • kubectl explain services.spec.type

Command

$ kubectl get pod

• List of pods
• -w option can be used. (–watch)

$ kubectl get all

• List of all objects on different layers

$ kubectl delete <replicaSet, pod> <pod name>

• Delete Pod

$ kubectl scale <replicaSet name> <pod name> --replicas <num>

• Update the number of replicas
• It is the same as 4 kubectl scale deployment (node name) --replicas <num>
• kubectl scale <short name replicaSets>/<pod name> --replicas <num>
  • ex) kubectl scale deploy/my-httpd –replicas
    • deploy = deployment = deployments

$ kubectl logs deploy/(pod name)

• option
  • –follow: works like -f option with tail
    • ex) kubectl logs deploy/my-apache --follow --tail 1
• 컨테이너 내부 로그 확인
• 많은 pod를 가지고 있더라도 하나만 가지고 와서 보여준다. 첫 라인에서 확인 가능.

$ kubectl describe <resource type> <pod name>

• It is very simliar to inspect command in docker
• 자세한 로그 확인 가능. 컨테이너 사양에 대해서도 확인 가능.

$ kubectl expose deployment/<pod name> --port <port number>

• To open port.
• Create clusterIP
  • expost command로 서비스를 생성하는 것!
  • clusterIP는 내부에서만 접속 가능하다! host OS 에서는 안 되는게 정상!
    • Linux host에서는 가능!
  • curl 등으로 확인하려면 새로운 pod를 생성해서 bash로 들어간 후에 curl을 날릴 수 있다.
    • service name이 DNS가 되기 때문에 curl my-httpd:(port)로 쓸 수 있다.
• ex) kubectl expose deploy/(node name) --port (port num) --name (alias) --type NodePort
• ex) kubectl expose deploy/(node name) --port (port num) --name (alias) --type LoadBalancer

NodePort 서비스 추가하기

• $ kubectl expose <resource name>/<pods name> --port <port number> --name <nodePort name> --type NodePort

• $ kubectl get service 를 해보면 추가되는걸 알 수 있는데 포트가 0000:30000 형식으로 되어있다.

  • :<외부에 노출되는="" IP="">

LoadBalancer 서비스 추가하기

• $ kubectl expose <resource name>/<pods>name> --port <port number> --name <loadBalancer name> --type LoadBalancer