k8s/StudyNotes

k8s/StudyNotes/cubectl k8s/StudyNotes/Deployments k8s/StudyNotes/Pods k8s/StudyNotes/Services

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kubeadm
- deploys all the kubernetes services downloaded from web
Kube-Scheduler
1. Filter Nodes (Pod cant fit)
2. Rank Nodes (Compare resources left, try to balance cpu/mem usage)
kubelet - captain on each Worker Node
- Registers with Master node, reports status and executes
- Always manual install wget https://storage.googleapis.com/kubernetes-release/release/v1.xx.x/bin/linux/amd64/kubelet
  - Not kubeadm managed.
  - Needs tls bootstrap
Kube-proxy - run on each node, service's virtual component
- All pods can see all other pods, through POD Network, by IP/Name. Exposed through service: eg. db(IP)
- Watches for service creation, and then configure network e.g. Iptables to forward to actual pod.
- Install: download wget to install or
  - kubeadm will deploy it as deamon set to each pod in namespace kube-system
PODs
- smallest object in k8s, contains containers, can contain one or more containers
- scale service by creating more pod instances.
- additional container could be helper container.
- network space is shared between containers in the same pod, they can communicate on localhost.
- k8s Controllers - the brains
  - kind: ReplicaSets - Replication controller -> newer -> Replica Sets
    1. yml definition ReplicationController same 4 sections as other configs
      - apiVersion: v1
      - kind: ReplicationController
      - metadata:
        name: myapp-rc labels:
        app: myapp type: front-end
      - spec:
        template:
        <pod definition nested, with same 2 sections, metadata, spec>
        replicas: 3
    2. yml definition newer ReplicationSet, requires selector:
```
         apiVersion: apps/v1
         kind: ReplicaSet
         metadata:
           name: myapp-rc
           labels:
             app: myapp
             type: front-end
           selector:
             app: myapp
             type: front-end
```
      - spec:
        template:
        <pod definition nested, with same 2 sections, metadata, spec>
        replicas: 3 selector:
        matchLabels:
        type: front-end
kind: Deployments - Encapsulates ReplicaSet that Encapsulate Pods
- Can have deployment and replacement policy
kind: ResourceQuote
- spec:
  - hard:
    - cpu:

kind: Service ,

Service-NodePort k8s-Obj-bind external node port to internal. NodePort is external port 30000-32767

         apiVersion: v1
         kind: Service
         metadata:
           name: myapp-service
         spec:
           type: NodePort
           ports:
            - targetPort: 80   ->POD
              port: 80         ->This service local ip port (Optional)
              nodePort: 30008  ->Node external port listening on host, same port on all Nodes!
           selector:
             app: myapp
             type: front-end

Service-!ClusterIP internal network, default type

         apiVersion: v1
         kind: Service
         metadata:
           name: back-end-service
         spec:
           type: ClusterIP   << Default if not specified
           ports:
            - targetPort: 80
              port: 80
           selector:
             name: my-app
             type: back-end

Service-LoadBalancer - Configure external LB

         apiVersion: v1
         kind: Service
         metadata:
           name: myapp-service
         spec:
           type: Loadbalancer
           ports:
            - targetPort: 80
              port: 80
              nodePort: 30008
           selector:
             name: my-app
             type: back-end