Kubernets

• Introduction
• kubetct
  • Update Resource
• Pods
• ReplicaSet
• Deployment
  • Update and Rollback
• Service

Quick

• All Alias

• kubectl get all
  

Introductions

It is used to deploy and orchestrate containers
It used multiple components to work :

• API server
  • front end
• etcd
  • key value
• kubelet
  • Agent that run in each node
• Container Runtime
  • docker for example
• Controler
  • healty check of container
• Scheduler
  • Distributing works across

Kubernetes use yaml or json format to describe configuration file.

Tow different nodes | Master Node | Worker Node | | :-: | :-: | | Control woker nodes | Run containers | | kube-apiserver
etcd
Controler
scheduler | kubelet
Container runtime |

kubectl

Resources Type

| Name | Full | Alias | | :-: | :-: | :-: | | Pod | pod | po | | Nodes | node | TODO | | ReplicaSet | replicaset | rs | | Deployment | deployment | deploy | | Service | service | svc |

Table Kind and Version | Kind | Version | | :-: | :-: | | Pod | v1 | | Service | v1 | | ReplicaSet | apps/v1 | | Deployment | apps/v1 |

Create a pod with a docker image

kubectl run <POD_NAME> --image=<IMAGE_NAME>

Get Cluster info :

kubectl cluster-info

Get list of resource

kubectl get <RESOURCE_TYPE>
# For more info use
kubectl get <RESOURCE_TYPE> -o wide
# Get all resources at once
kubectl get all
# Get some different resources type at once
kubectl get <RESOURCE_TYPE>,<RESOURCE_TYPE>,<RESOURCE_TYPE>,...

Get description on a resource

Usage:
  kubectl describe (-f FILENAME | TYPE [NAME_PREFIX | -l label] | TYPE/NAME) [options]

Delete a resource

Usage:
  kubectl delete ([-f FILENAME] | [-k DIRECTORY] | TYPE [(NAME | -l label | --all)]) [options]

Update the definition : 3 methods

1. Direct edit

   kubectl edit <RESOURCE_TYPE> <RESOURCE_NAME>
   

2. Scale

   kubectl scale replicaset <REPLICASET_NAME> --replicas=5
   kubectl scale -f <YAML_FILE> --replicas=5
   

3. YAML

   kubectl <replace | apply | patch> -f <YAML_FILE>
   

PODS

DESC : pod are a single instance of an application

Pod
Offen containe only one docker
We can have multiple docker that do different stuff
Docker in the same pod can access each other with localhost

Start a pods with a yaml definition

kubectl create -f <YAML_FILE>

Pod configuration are structured as follow

apiVersion: <VERSION> # See Kind and Version
kind: <KIND>          # See Kind and Version
metadata:
  name: <POD_NAME>
  labels:             # you can create every labels you want for example :
    app: myapp
    type: front-end
spec:
  containers:         # array of container with name and image like so
    - name: <CONTAINER_NAME>
      image: <DOCKER_IMAGE>

Adding environments variables

spec:
  containers:
    - [...]
      env:            # Array of name value
        - name: <ENV_VAR_NAME>
          value: <ENV_VAR_VALUE>

ReplicaSet

DESC : Replica Set are use to manage multiple pods at the same time.

ReplicatSet configuration are structured as follow

apiVersion: apps/v1   # See Kind and Version
kind: ReplicaSet      # See Kind and Version
metadata:
  name: <REPLICATSET_NAME>
  labels:             # You can create every labels you want for example :
    <REPLICATSET_LABEL_NAME>: <REPLICATSET_LABEL_VALUE>
spec:
  selector:           # Select the Pods to managed
    matchLabels:
      <POD_LABEL_NAME>: <POD_LABEL_VALUE>
  replicas: 3         # Number of Pods to be created
  template:           # Template of a Pod definition with label match with selector
    [POD DEFINITION]

Start the ReplcaSet with a yaml definition

kubectl create -f <YAML_FILE>

Deployment

DESC : Deployment is a higher-level concept that manages ReplicaSets and provides declarative updates to Pods along with a lot of other useful features

Deployment configuration are structured as ReplicaSet exept for kind field

apiVersion: apps/v1   # See Kind and Version
kind: Deployment      # See Kind and Version
metadata:
  name: <DELPOYMENT_NAME>
  labels:             # You can create every labels you want for example :
    <DELPOYMENT_LABEL_NAME>: <DEPLOYMENT_LABEL_VALUE>
spec:
  selector:           # Select the Pods to managed
    matchLabels:
      <POD_LABEL_NAME>: <POD_LABEL_VALUE>
  replicas: 3         # Number of Pods to be created
  template:           # Template of a Pod definition with label match with selector
    [POD DEFINITION]

Update and rollback

Strategies	Description
Recreate	1. destroy all 2. recreate all
Rolling Update	1. destroy and recreate one by one Is the default strategie

To Update see Update Resource with YAML

Manage the rollout of one or many resources.

Valid resource types include:
  *  deployments
  *  daemonsets
  *  statefulsets

Available Commands:
  history       View rollout history
  pause         Mark the provided resource as paused
  restart       Restart a resource
  resume        Resume a paused resource
  status        Show the status of the rollout
  undo          Undo a previous rollout

Usage:

kubectl rollout SUBCOMMAND [options]

Example:

# Rollback to the previous deployment
kubectl rollout undo deployment/abc

# Restart a deployment
kubectl rollout restart deployment/abc

# Restart deployments with the app=nginx label
kubectl rollout restart deployment --selector=app=nginx

Service

DESC : Use to manage connection between deployments

Service Type	Description
NodePort	Made internal pod accessible from a Node through a port
ClusterIp	Virtual IP to have multiple pods accessible through one IP, default value of spec.type
Load Balancer	Load Balance the workload to multiple instance, see compatible cloud providers (gcp, aws, azure)

All Service Type configuration are structured as follow:

apiVersion: v1
kind: Service
metadata:
  name: <SERVICE_NAME>
spec:
  [See spec bellow]

Get URL of a service:

minikube service <SERVICE_NAME> --url

• NodePort example

  spec:
    type: NodePort
    port:
      - targetPort: 80
        port: 80
        nodePort: 30008
    selector:
      [LABEL_NAME]: [LABEL_VALUE]
  

• ClusterIP example

  spec:
    type: ClusterIP
    port:
      - targetPort: 80
        port: 80
    selector:
      [LABEL_NAME]: [LABEL_VALUE]
  

• Load Balancer : see with your clouds providers