how to setup Azure Kubernetes Service cluster and configure Kubernetes dashboard with AZ CLI?

it is very easy to create and run a  AKS cluster with few AZ CLI commands.

1. create a resource group for AKS

az group create --name dan-aks-rg --location eastus

2. create an AKS cluster

az aks create --resource-group dan-aks-rg --name dan-cluster

3.get the credentials for the cluster, this will download the credetenials and store in the config file
under this path C:\Users\admin\.kube

az aks get-credentials --resource-group dan-aks-rg --name dan-cluster

4. install the Kubernetes cli utility

az ask install-cli

5. install Kubernetes dashboard

kubectl apply -f https://raw.githubusercontent.com/kubernetes/dashboard/v2.0.0/aio/deploy/recommended.yaml

6. Access the dashboard. there are two way to access the Kubernetes dashboard.
 from AZ CLI

az aks browse --resource-group dan-aks-rg --name dan-cluster

it will automatically lauch in the web browser

http://127.0.0.1:8001/api/v1/namespaces/kube-system/services/https:kubernetes-dashboard:/proxy/


or we can use kubectl proxy to access the Kubernetes Dashboard UI. Type Kubectl proxy in the CMD windows, then hit enter and launch the web chrome and paste the following url in the url windows to launch the kubernetes dashboard.

kubectl proxy 

http://localhost:8001/api/v1/namespaces/kubernetes-dashboard/services/https:kubernetes-dashboard:/proxy/#/overview?namespace=default

7. Trouble shot tips

if you see an empty kubernetes dashboard with warming message
"secrets is forbidden: User "clusterUser" cannot list resource "secrets" in API group "" in the namespace "default"

it is permission issue. you can resolve this following steps, you need to replace the clusterUser with specific name that was shown in your error message.

• kubectl delete clusterrolebinding kubernetes-dashboard
  
  kubectl delete clusterrolebinding kubernetes-dashboard -n kube-system
  
  kubectl create clusterrolebinding kubernetes-dashboard --clusterrole=cluster-admin --serviceaccount=kube-system:kubernetes-dashboard --user=clusterUser

https://kubernetes.io/docs/reference/generated/kubectl/kubectl-commands#-em-clusterrolebinding-em-

how to use build-in debugger to debug a Node.js appliation?

it is very important to trouble shot an issue or bug in the application development. i will show you how to use the debug tools that built into Node, that let you step through the code.

step 1. add debugger; before the line that you want to debug

 show: (req, res, next) => {

    let userId = req.params.id;

    User.findById(userId)

      .then(user => {

        debugger;

        res.locals.user = user;

        next();

      })

      .catch(error => {

        console.log(`Error fetching user by ID: ${error.message}`);

        next(error);

      });

  },

step 2. run node --inspect-brk main.js command in your project's terminal window to launch the build in debugger

C:\code\Node\unit5\recipe_app (master) (capstone@1.0.0)
λ node --inspect-brk main
Debugger listening on ws://127.0.0.1:9229/d66cdcb4-12df-4f71-80db-43d9c5ba6adc
For help, see: https://nodejs.org/en/docs/inspector
Debugger attached.

step 3. launch the chrome browse and type chrome://inspect in the url window.

click on the inspect link. it will start breaking at the first line of main.js









you can either go to line by line with press F10 function or key or press the continue button to go the the line of code with debugger;

you can also go to the node tab under source section, then you can pick anything javascript files to set the breakpoint in order to inspect or trace the code and values

now you can easily fix the trouble code.

how to run a node.js application in debug mode?

it is very convenient to trouble shot a node.js application when we run it under debug mode.

here is the line that we can execute in the command line within the project folder in the CMD

set DEBUG=* & node main (for project with main.js as the start up file)

or
set DEBUG=* & node index (for project setting index.js as the entry point.

or we can add the following code to the script section in the package.json file.

"debug": "set DEBUG=* node main"


here is the sample from my node.js application.

  "scripts": {

    "start": "node main.js",

    "test": "echo \"Error: no test specified\" && exit 1",

    "debug": "set DEBUG=* & node main"

  },

then we can start the application with the following line

npm run debug

how to test JWT token with CURL in command line?

after we implement api to load the JWT with basic authentication via login form that requried user to provide email and password in order to access the api with JWT authorization.

it is very to easy to test the logic by executing the following command line in CMD/cmder

curl -d "email=test@email.com&password=test1234" http://localhost:3000/api/login

the output is below indicating that the JWT token is generated with provided login information.

λ curl -d "email=test@email.com&password=test1234" http://localhost:3000/api/login
{"success":true,"token":"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJkYXRhIjoiNW
VmYTA5ZWEzMGE2ZTAwYzIwMmJhNjhiIiwiZXhwIjoxNTkzNTQ0NDM4NzE2L
CJpYXQiOjE1OTM0NTgwMzh9.IHTlnRuOg_AlppmraGMY8xibrGNAoGGSMA3yGx_2DmI"}

how to use environment variable in Node.js and Express Server development?

it is very convenient to use environment variable during the web development with express server and Node.js

here is the steps to configure the environment variable in the  project.

1. add a .env file to the project folder.

2. install the dotenv package
    npm i dotenv -S

3. add dotnet library to the file that will load the environment variable. in my case it is from a controller

dotenv = require('dotenv');

dotenv.config();

4. add required variables to the .env file

#test token
TOKEN=recipeT0k3n

# API
API_TOKEN=recipeAPIT0k3n

5. load the environment variable, it must be the same file in the step 3

const token=process.env.TOKEN || "recipeT0k3n",

or you can define it as global variable in the index.js or main.js with the following snippet of code

dotenv = require('dotenv');

dotenv.config();

export const token=process.env.TOKEN || "recipeT0k3n",

Handy npm commands

1. use npm init to generate a package.json file for the application

2. use npm install --save flag to mark the package as an application dependency.

for example when i ran npm install express --save, the process will automatically add express to the
dependencies section.

use npm install --save-dev to install the library for the development of an application only

{

  "name": "first_express_project",

  "version": "1.0.0",

  "description": "first web project build with express",

  "main": "main.js",

  "scripts": {

    "test": "echo \"Error: no test specified\" && exit 1"

  },

  "author": "Dan Deng",

  "license": "ISC",

  "dependencies": {

    "express": "^4.17.1"

  }

}

3.  run npm docs library name to access the library documentation.

for example npm docs express will launch the default web browser to http://expressjs.com.

4. npm i nodemon -g to install the node monitor package to force restart the application. after any change to the project.
use the following configuration to setup nodemon to run the application

 "scripts": {

    "start":"nodemon main.js",

    "test": "echo \"Error: no test specified\" && exit 1"

  },

then run npm start to launch the application.

λ npm start

> first_express_project@1.0.0 start C:\code\Node\first_express_project
> nodemon main.js

[nodemon] 2.0.4
[nodemon] to restart at any time, enter `rs`
[nodemon] watching path(s): *.*
[nodemon] watching extensions: js,mjs,json
[nodemon] starting `node main.js`
The express server has started and is listening on port number : 3000

how to implement a simple typesafe assertion library in Typescript?

we can assert typesafe to ensure that parameters with specific type in typescript.

here i will demostrate a simple function to ensure that input parameters are the same type

type is={

    <T>(a: T, b:T):boolean

}

let isSame:is=<T>(

    first:T,

    second:T

)=>{

    return first==second;

}

function print(b:boolean){

    console.log(b);

}

print(isSame("string","anotherString"));

print(isSame(true,false));

print(isSame(42, 42));

print(isSame(10, 'foo'));

src/index.ts:73:18 - error TS2345: Argument of type '"foo"' is not assignable to parameter of type 'number'.

73 print(isSame(10, 'foo'));
                    ~~~~~


Found 1 error.



we can easily get the catch the error in compile time. that is the magic of typesafe in typescript, the compiler enforce the type-safe check in the compile time.