Kubernetes

Kubernetes is an open-source system for automating deployment, scaling, and management of containerized applications.

Features

Service discovery and load balancing

Automatic binpacking

Storage orchestration

Self-healing

Automated rollouts and rollbacks

Secret and configuration management

Batch execution

Horizontal scaling

Pods and services in Kubernetes have their own IP; however, it is normally not the interface you’d provide to the external internet. Though there is service with node IP configured, the port in the node IP can’t be duplicated among the services. It is cumbersome to decide which port to manage with which service. Furthermore, the node comes and goes, it wouldn’t be clever to provide a static node IP to external service.

Ingress defines a set of rules that allows the inbound connection to access Kubernetes cluster services. It brings the traffic into the cluster at L7, allocates and forwards a port on each VM to the service port. This is shown in the following figure. We define a set of rules and post them as source type ingress to the API server. When the traffic comes in, the ingress controller will then fulfill and route the ingress by the ingress rules. As shown in the following figure, ingress is used to route external traffic to the kubernetes endpoints by different URLs:

https://www.packtpub.com/mapt/book/virtualization_and_cloud/9781788396646/5/ch05lvl1sec25/ingress

Setup:

Install Virtualbox

Install kubectl

brew install kubernetes-cli

Install minikube

brew cask install minikube
minikube start

Get all namespaces

kubectl get namespaces

Create new namespace

namespace-balram.json

{
 “kind”: “Namespace”,
 “apiVersion”: “v1”,
 “metadata”: {
 “name”: “balram”,
 “labels”: {
 “name”: “balram”
 }
 }
}

Run command

kubectl create -f namespace-balram.json

ref: https://kubernetes.io/docs/tasks/administer-cluster/namespaces-walkthrough/

See Kubectl config

kubectl config view

I got below response

apiVersion: v1
clusters:
- cluster:
certificate-authority: /Users/balsingh1/.minikube/ca.crt
server: https://192.168.99.101:8443
name: minikube
contexts:
- context:
cluster: minikube
user: minikube
name: minikube
current-context: minikube
kind: Config
preferences: {}
users:
- name: minikube
user:
client-certificate: /Users/balsingh1/.minikube/client.crt
client-key: /Users/balsingh1/.minikube/client.keyapiVersion: v1

Run

kubectl config current-context

Got response

minikube

The next step is to define a context for the kubectl client to work in each namespace. The value of “cluster” and “user” fields are copied from the current context.

kubectl config set-context dev --namespace=balram \
>   --cluster=minikube \
>   --user=minikube

Response

Context "dev" created.

Recheck config

kubectl config viewGot response

Response

apiVersion: v1
clusters:
- cluster:
certificate-authority: /Users/balsingh1/.minikube/ca.crt
server: https://192.168.99.101:8443
name: minikube
contexts:
- context:
cluster: minikube
namespace: balram
user: minikube
name: dev
- context:
cluster: minikube
user: minikube
name: minikube
current-context: minikube
kind: Config
preferences: {}
users:
- name: minikube
user:
client-certificate: /Users/balsingh1/.minikube/client.crt
client-key: /Users/balsingh1/.minikube/client.key

Let’s switch to operate in the development namespace.

kubectl config use-context dev

You can verify your current context by doing the following:

kubectl config current-context

response

dev

At this point, all requests we make to the Kubernetes cluster from the command line are scoped to the balram namespace.

Let’s create some contents.

kubectl run snowflake --image=kubernetes/serve_hostname --replicas=2

We have just created a deployment whose replica size is 2 that is running the pod called snowflake with a basic container that just serves the hostname. Note that kubectl run creates deployments only on Kubernetes cluster >= v1.2. If you are running older versions, it creates replication controllers instead. If you want to obtain the old behavior, use --generator=run/v1 to create replication controllers. See kubectl runfor more details.

kubectl get deployment

Response

NAME        DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
snowflake   2         2         2            2           1m
kubectl get pods -l run=snowflake

response

NAME                         READY   STATUS    RESTARTS   AGE
snowflake-54fccfcd67-dflkh   1/1     Running   0          8m
snowflake-54fccfcd67-lww4w   1/1     Running   0          8m

Ingress

ref

https://kubernetes.io/docs/concepts/workloads/pods/pod/

https://kubernetes.io/docs/concepts/workloads/controllers/deployment/

https://kubernetes.io/docs/concepts/services-networking/service/

Ingress

Kubernetes NodePort vs LoadBalancer vs Ingress? When should I use what?

Command to get IP of service if it is saying pending in kubectl get services

minikube service list