k8s/StudyNotes

k8s/StudyNotes/cubectl k8s/StudyNotes/Deployments

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* kubeadm

deploys all the kubernetes services downloaded from web

* Kube-Scheduler

Filter Nodes (Pod cant fit)
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
  - 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
      - spec:
        template:
        <pod definition nested, with same 2 sections, metadata, spec>
        replicas: 3 selector:
        matchLabels:
        type: front-end