Kubernetes.txt

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Commands

kubectl --namespace=acp-system scale deployment acp-upgrade --replicas=0


$ kubectl get nodes
$ kubectl get events


$ kubectl config get-contexts
$ kubectl config use-context <context-name>

$ kubectl run <deployment-name> --image=<image-location> --port=<port-num>
$ kubectl expose deployment <deployment-name> --type=NodePort

$ kubectl explain

Kubernetes Structure:
1) 'kubectl' is entry to Kubernetes cluster
2) Controller Manager controls cluster-level functions
3) Scheduler talks to nodes to allocate resources
4) nodes then host pods
5) kube-proxy runs on each node and controls the network on nodes
6) pods then have groups of docker containers in them
7) docker containers share the same logical volume

Definitions:
POD: A group of coordinating containers. It's the smallest unit the Scheduler
understands. The containers within the pod share some context and interact,
directly or indirectly, with each other.

NODES: Closely associated with machines no network

SERVICES:

KUBE-PROXY: Manages network access on a node. Controls access to services on
the node. It also does load balancing.

SCHEDULER: Which Nodes have available resources and runs Pods on them.

CONTROLLER MANAGER: controls all other cluster level functions

KUBECTL: Talks to REST endpoint (Scheduler/Controller Mgr) to make it do
things


===============  KUBERNETES 101  ==============

- Kubernetes have 2 _types_ of nodes: HEAD Node and WORKER Nodes

- What's in a HEAD node?
-----------
    * API Server: Exposes APIs
    * Scheduler: Decides where to schedule pods, on which m/c etc
    * Controller Manager: Makes sure state of cluster in right shape
    * Etcd: Storage. It's possible etcd is outside the cluster
    * Sometimes:
        - kubelet: agent running on HEAD. Managed by systemd
        - docker

- kubelet config is in /etc/systemd/system/kubelet.service.d/10-kubeadm.conf
- Manifest files will be (usually) in: /etc/kubernetes/manifests/
        * bunch of YAML files in this directory


- What's in WORKER node? Lots of them.
-----------
    * kubelet: agent running on all WORKER nodes. It talks to API server on
      HEAD and local docker containers to manage them
    * kube-proxy: manages IP tables in that node
    * docker

POD:
- Lowest unit of computing maintained by kubectl

Installing Kubernetes (3 techniques)
----
- First install kubectl (brew install kubectl on MacOS)
- minikube
- GKE (Google Kubernetes Engine)
- kubeadm



COMMANDS
--------
$ systemctl status kubelet      # gives status of kubernetes on that node


$ minikube start
$ minikube status
$ kubectl version
$ kubectl get nodes

$ kubectl get pods
$ kubectl delete pod <pod-name>


$ kubectl -v=9 [command]    // very verbose. Underlying call is 'curl'

$ kubectl api-version       // gives all api GROUPS in the cluster

$ kubectl label pods <pod-name> [key=value] // key: value will sit in metadata
                                            // of the pod
$ kubectl get pods label <pod-name>         // returns all labels of the pod

$ kubectl get rs    // gets replicasets
$ kubectl scale rs <replicaset-name> --replicas=<number>



kubectl get deployments
kubectl get deployment <my-dep>
kubectl get nodes
kubectl get pods --all-namespaces


// debug command if pod fails to get deployed
kubectl describe pod <pod-name>

//
kubectl describe deployment <pod-name/deployment-name>

// deploy an image
kubectl run <depl-name> --image=<image-location>

// get top level status of pods
kubectl get pods

// more info about a pod
kubectl describe pod <pod-name>

kubectl logs <pod-name>

// if a pod is restarted, previous logs can still be seen as
kubectl logs <pod-name> --previous

kubectl create configmap <name> --from-file=<directory or file>
kubectl describe configmap <name>


kubectl get deployments
kubectl get deployment <name> -o yaml

kubectl get configmaps
kubectl get configmap <name> -o yaml

kubectl scale deploy <deployment-name> --replicas=<number>

[1] https://kubernetes.io/docs/reference/kubectl/cheatsheet/


[1] Safari Books Online: Kubernetes Fundamentals - Sebastien Goasguen
[2] kubernetes.io
[3] cncf.io
[4] github.io/kubernetes-incubator


Resources:
[1] O'Reilly Kubernetes Bootcamp: Get up to speed with Docker and Kubernetes -
Zed Shaw




@@@@@@@@@@@@@@@@@@@   KUBERNETES  CHEAT  SHEET    @@@@@@@@@@@@@@@@@@

Kubectl Autocomplete
BASH
    source <(kubectl completion bash) # set up autocomplete in bash into the current shell, bash-completion package should be installed first.
    echo "source <(kubectl completion bash)" >> ~/.bashrc # add autocomplete permanently to your bash shell.

Shorthand alias for kubectl
    alias k=kubectl
    complete -o default -F __start_kubectl


ZSH
    source <(kubectl completion zsh)  # set up autocomplete in zsh into the current shell
    echo '[[ $commands[kubectl] ]] && source <(kubectl completion zsh)' >> ~/.zshrc # add autocomplete permanently to your zsh shell



Resource:
https://kubernetes.io/docs/reference/kubectl/cheatsheet/