Kubernetes - Building NodeJS Application and deployment - Recreate Strategy

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Now we'll build a simple Node.js web application and package it into a container image. 

The application will accept HTTP requests and respond with the hostname of the machine it's running in.

root@masterk8s:/kube# mkdir nodejs

root@masterk8s:/kube# cd nodejs/

root@masterk8s:/kube/nodejs# vi app.js

root@masterk8s:/kube/nodejs# cat app.js

const http = require('http');

const os = require('os');

console.log("My server starting and listening on 8080...");

var handler = function(request, response) {

  console.log("Received request from " + request.connection.remoteAddress);

  response.writeHead(200);

  response.end("You've hit " + os.hostname() + "\n");

};

var www = http.createServer(handler);

www.listen(8080);

root@masterk8s:/kube/nodejs#


It starts up an HTTP server on port 8080. The server responds with an HTTP response status code 200 OK and the text "You've hit <hostname>" to every request. 

The request handler also logs the client's IP address to the standard output, which we'll need later.

root@masterk8s:/kube# cat Dockerfile

FROM node:7

ADD nodejs/app.js /app.js

ENTRYPOINT ["node", "app.js"]

root@masterk8s:/kube#


root@masterk8s:/kube# docker build . -t rajasekar/node-web-v1

Sending build context to Docker daemon   47.1kB

Step 1/3 : FROM node:7

 ---> d9aed20b68a4

Step 2/3 : ADD nodejs/app.js /app.js

 ---> ec9668d794c4

Step 3/3 : ENTRYPOINT ["node", "app.js"]

 ---> Running in c383f70fb199

Removing intermediate container c383f70fb199

 ---> 67e44dc71429

Successfully built 67e44dc71429

Successfully tagged rajasekar/node-web-v1:latest

root@masterk8s:/kube#


root@masterk8s:/kube# docker run --name my-app -p 8080:8080 -d 67e44dc71429

7883bf20192fed68d39587831878f6b4b19bd426073dc8b85903e6bb1bb90ade

root@masterk8s:/kube#

root@masterk8s:/kube# docker container ls  | grep -i my-app

7883bf20192f   67e44dc71429           "node app.js"            24 seconds ago   Up 22 seconds   0.0.0.0:8080->8080/tcp, :::8080->8080/tcp   my-app

root@masterk8s:/kube#

root@masterk8s:/kube# curl 0.0.0.0:8080

You've hit 7883bf20192f

root@masterk8s:/kube#


Since, I have one worker node. I am going to take backup of this image and restore in worker node.

root@masterk8s:/tmp# docker save rajasekar/node-web-v1 -o /tmp/node-web-v1.tar

root@masterk8s:/tmp# ls -l /tmp/node-web-v1.tar

-rw------- 1 root root 681218048 May  2 21:16 /tmp/node-web-v1.tar

root@masterk8s:/tmp#


On the worker node:

root@worker1:/tmp# docker load < /tmp/node-web-v1.tar

Now, Lets use this image to do a k8s deployment.

apiVersion: apps/v1

kind: Deployment

metadata:

  name: node-app

spec:

  selector:

    matchLabels:

      app: nodejs

  template:

    metadata:

      labels:

        app: nodejs

    spec:

      containers:

      - name: nodejs-v1

        image: rajasekar/node-web-v1:latest

        imagePullPolicy: Never

        ports:

        - containerPort: 8080


root@masterk8s:/kube# kubectl get pods

NAME                        READY   STATUS    RESTARTS   AGE

node-app-565bc4d7dc-xjjwg   1/1     Running   0          5s

root@masterk8s:/kube#


root@masterk8s:/kube# kubectl scale deployment node-app --replicas=3

deployment.apps/node-app scaled

root@masterk8s:/kube# kubectl get pods

NAME                        READY   STATUS              RESTARTS   AGE

node-app-565bc4d7dc-csf68   0/1     ContainerCreating   0          2s

node-app-565bc4d7dc-xjjwg   1/1     Running             0          29s

node-app-565bc4d7dc-zrvjs   0/1     ContainerCreating   0          2s

root@masterk8s:/kube# kubectl get pods

NAME                        READY   STATUS    RESTARTS   AGE

node-app-565bc4d7dc-csf68   1/1     Running   0          4s

node-app-565bc4d7dc-xjjwg   1/1     Running   0          31s

node-app-565bc4d7dc-zrvjs   1/1     Running   0          4s

root@masterk8s:/kube#


Lets expose this deployment to a NodePort service.

root@masterk8s:/kube# kubectl expose deployment node-app --type NodePort --port 8080 --target-port 8080

service/node-app exposed

root@masterk8s:/kube# kubectl get svc

NAME         TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE

node-app     NodePort    10.102.49.246   <none>        8080:32253/TCP   3s

root@masterk8s:/kube#

root@masterk8s:/kube# kubectl get ep

NAME         ENDPOINTS                                            AGE

node-app     10.244.1.10:8080,10.244.1.11:8080,10.244.1.12:8080   20s

root@masterk8s:/kube#


Lets test by hittig the cluster IP on port 8080:

root@masterk8s:/kube# curl 10.102.49.246:8080

You've hit node-app-565bc4d7dc-zrvjs

root@masterk8s:/kube# curl 10.102.49.246:8080

You've hit node-app-565bc4d7dc-xjjwg

root@masterk8s:/kube# curl 10.102.49.246:8080

You've hit node-app-565bc4d7dc-csf68

root@masterk8s:/kube#


We are able to hit the pods behind the deployment.

Now, I am going to make changes to my image with some modification and create new image. Load the new image [rajasekar/node-web-v2] across the workers.


apiVersion: apps/v1

kind: Deployment

metadata:

  name: node-app

spec:

  selector:

    matchLabels:

      app: nodejs

  template:

    metadata:

      labels:

        app: nodejs

    spec:

      containers:

      - name: nodejs-v2

        image: rajasekar/node-web-v2:latest

        imagePullPolicy: Never

        ports:

        - containerPort: 8080


root@masterk8s:/kube# kubectl get pods

NAME                        READY   STATUS        RESTARTS   AGE

node-app-565bc4d7dc-csf68   1/1     Terminating   0          23m

node-app-565bc4d7dc-xjjwg   1/1     Terminating   0          23m

node-app-565bc4d7dc-zrvjs   1/1     Terminating   0          23m

node-app-5c97994c4c-7hnsh   1/1     Running       0          27s

node-app-5c97994c4c-t97pk   1/1     Running       0          32s

node-app-5c97994c4c-tkdjg   1/1     Running       0          30s

root@masterk8s:/kube# 


root@masterk8s:/kube# curl 10.102.49.246:8080

You've hit node-app-5c97994c4c-tkdjgThis is a secure link of version 99.99%

root@masterk8s:/kube# curl 10.102.49.246:8080

You've hit node-app-5c97994c4c-7hnshThis is a secure link of version 99.99%

root@masterk8s:/kube# curl 10.102.49.246:8080

You've hit node-app-5c97994c4c-7hnshThis is a secure link of version 99.99%

root@masterk8s:/kube#


If you looks closely, We have not changed anything other than the container name and image. So, when we deploy this delete V1 pods and V2 pods becomes active.

This deployment is called "RECREATE Deployment".







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