Helm Chart for MySQL in GKE

Here is how to deploy and test connectivity of MySQL in Google Kubernetes Engine GKE

# connect to cluster in Google Kubernetes Engine
$ gcloud container clusters get-credentials <your-cluster> --zone <your-zone> --project <your-project>
$ git clone --depth=1 https://github.com/helm/charts.git
$ cd charts/stable/mysql
$ vim values.yaml
$ helm install --name dbserver -f values.yaml stable/mysql
$ kubectl get pods
$ MYSQL_ROOT_PASSWORD=$(kubectl get secret --namespace default dbserver-mysql -o jsonpath="{.data.mysql-root-password}" | base64 --decode; echo)
$ echo $MYSQL_ROOT_PASSWORD
$ kubectl run -i --tty ubuntu --image=ubuntu:16.04 --restart=Never -- bash -il
root@ubuntu:/# apt-get update && apt-get install mysql-client -y
root@ubuntu:/#  mysql -h dbserver-mysql -p
mysql> exit
root@ubuntu:/# exit
$ kubectl get pvc
$ kubectl get pv
 
# clean up
$ helm delete --purge dbserver
$ kubectl delete pod/ubuntu

Useful JavaScript Snippets

By using lodash you can loop through arrays and objects with ease

const _ = require("lodash");
// replace object in array
var arr = [{ id: 1, name: "Adam" }, { id: 2, name: "Bob" }];
var index = _.findIndex(arr, { id: 1 });
arr.splice(index, 1, { id: 100, name: "New man" });
document.write(JSON.stringify(arr));
document.write(`<hr/>`);
// update object in array
var mike = { id: 17, name: "mike" };
var newMike = { id: 17, name: "New Mike" };
var updatedMike = _.merge(mike, newMike);
document.write(JSON.stringify(updatedMike));
document.write(`<hr/>`);
// iterate over object using key value
const obj = { a: [76, 23], b: ["en", "es"]}
const result = _.map(obj, (value, key) => {
  document.write(`pair: ${key} : ${value[0]} <br />`);
});
document.write(`<hr/>`);
// filter array of objects by property 
var users = [
  { 'user': 'Adam', 'age': 36, 'active': false },
  { 'user': 'Bob', 'age': 40, 'active': false }
];
var flint = _.filter(users, o => o.age === 40)
document.write(JSON.stringify(flint));

Dealing with undefined in ternary operator

let element;
let item = typeof element === 'undefined' ? 'no val' : element;
  
console.log(item) // no val

Adding an element to a object

    let item = {id: 119 ,name: 'clothing', amount: 45}
 
    // no mutation add at the end of element
    let newItem1 = Object.assign({}, item, {category: 'Personal'})
    console.log(item);
    console.log(newItem1);
 
    // mutate add to end of element
    item = Object.assign(item, {category: 'Personal'});
    console.log(item);
 
    // proces array add at the end of every element
    let collection: any[] = []
    let items = [
      {id: 119 ,name: 'clothing', amount: 45},
      {id: 118 ,name: 'umbrela', amount: 47}
    ]
 
    items.map((item) => collection.push({...item, key4:"val4"}))
    console.log(collection);

Clone and modify existing element in clone. Great for setState in react.

const arrayOfObjects = [
  {name:"adam", isChecked: false},
  {name:"bob", isChecked: false}
]
 
let clone = arrayOfObjects.map((item) => ({...item}));
 
clone.map((item) => item.isChecked = true)
 
clone.map((item)=> console.log("clone ",item.name, item.isChecked))
arrayOfObjects.map((item)=> console.log("arrayOfObjects ",item.name, item.isChecked))

Images, Containers and Docker Registry

This tutorial shows how to create images and containers and push to hub.docker.com registry. GitHub repo is at https://github.com/nikola-bodrozic/Docker-ReactJS

Simple Build on Linux

Apache web server no Dockerfile, $(pwd) prints path to current folder

docker run -d --name apa -e TZ=UTC -p 8080:80 -v $(pwd)/html/:/var/www/html/ ubuntu/apache2

Development Build

docker build -t reactapp:1.0 .

docker run -p 3000:3000 \ 
       --env REACT_APP_BASE_URL=localhost \ 
       --name react-app reactapp:1.0

docker logs -f YOUR_CONTAINER_SHA

Prod build & push to registry

Create empty private image repo at DOCKER_HUB_USERNAME/REPO_NAME

The repo should be visible in browser at https://hub.docker.com/repository/docker/DOCKER_HUB_USERNAME/REPO_NAME

For production you need to set env variable in Dockerfile-prod not in docker run. Here's how
RUN REACT_APP_BASE_URL=example.com yarn build

build, run and push to registry

docker run -d \
           -p 80:80 \
           --name react-app-prod DOCKER_HUB_USERNAME/REPO_NAME:1.0

docker build -t DOCKER_HUB_USERNAME/REPO_NAME:1.0 \
             -f Dockerfile-prod .

docker login

docker push DOCKER_HUB_USERNAME/REPO_NAME:1.0

DOCKER_HUB_USERNAME/REPO_NAME:1.0

Override env. variable and shell script

Override env. variable and shell script defined in Docker file in run command.

build an image

docker build -t busybox .

run container with env. variable & run CMD in Dockerfile

docker run busybox

override env. variable in Dockerfile

docker run --env ENV_TARGET=yahoo.com busybox

override CMD in Dockerfile

docker run busybox sh -c 'whoami && pwd'

Dockerfile

FROM busybox

WORKDIR /app
ENV ENV_TARGET google.com
COPY subs.sh subs.sh
RUN chmod +x subs.sh
CMD ["/app/subs.sh"]

subs.sh

#!/bin/sh

ping -c 2 ${ENV_TARGET}

axios concurrent calls

Axios can make multiple concurrent calls. In app.js calls to two end-points are started at the same time so total waiting time is 4 seconds. Server latency is 4 seconds for demo purposes.

app.js

const axios = require('axios')
 
try {
    console.log("start");
    function getUserName() {
        return axios.get('http://localhost:3000/heroes');
    }
 
    function getId() {
        return axios.get('http://localhost:3000/heroes');
    }
 
    // Performing multiple concurrent requests waiting time 4 seconds
    axios.all([getUserName(), getId()])
        .then(axios.spread(function (acct, perms) {
            const user = acct.data[0].param;
            const id = perms.data[1].param;
            console.log(`${user} ${id}`)
            const str = 'https://jsonplaceholder.typicode.com/' + user + '/' + id
            console.log(str)
            axios.get(str).then(response => console.log(response.data.name));
        }));
} catch (error) {
    console.error(error);
}

axios async await

Sometimes you need to wait for one (axios) call to finish to continue with next one. It's accomplished by using async/await. Last axios call in app.js downloads a file without waiting for getUser() to be finished.

set server delay to 4 seconds for demo purposes

{
  "name": "async-await",
  "scripts": {
    "serve-json": "json-server --delay 4000 --watch db.json",
    "start": "node app.js"
  },
  "dependencies": {
    "axios": "^0.19.0",
    "json-server": "^0.15.0"
  }
}

db.json

{
    "heroes": [
        {
            "param": "users"
        },
        {
            "param": "1"
        }
    ]
}

app.js

const axios = require('axios')
const fs = require('fs')
 
async function getUser() {
    try {
        console.log("start");
        const response = await axios.get('http://localhost:3000/heroes');
        var1 = response.data[0].param; // users
        console.log("4 sec after start ", var1);
        const response2 = await axios.get('http://localhost:3000/heroes');
        var2 = response2.data[1].param; // 1
        console.log("8 sec after start", var2);
        const response3 = await axios.get('https://jsonplaceholder.typicode.com/' + var1 + '/' + var2);
        console.log(response3.data.name);
    } catch (error) {
        console.error(error);
    }
}
 
getUser()
 
// call below doesnot wait for getUser() to be finished 
axios({
    method: 'get',
    url: 'https://jsonplaceholder.typicode.com/users/2',
    responseType: 'stream'
  })
    .then(function (response) {
      response.data.pipe(fs.createWriteStream('full-user.json'))
});

Oracle 12c Create Table with Auto Increment and Flashback

CREATE TABLE table_name ( 
    id NUMBER(10) GENERATED BY DEFAULT AS IDENTITY ( START WITH 1 NOCACHE ) NOT NULL, 
    ctimestamp TIMESTAMP DEFAULT current_timestamp 
) NOLOGGING; 

CREATE UNIQUE INDEX table_name_pk ON table_name (id ASC ); 

ALTER TABLE table_name ADD CONSTRAINT table_name_pk PRIMARY KEY ( id ); 

SELECT TO_CHAR (SYSDATE, 'YYYY-MM-DD HH24:MI:SS') "NOW" FROM DUAL; 

CREATE TABLESPACE archivetest_tabspace DATAFILE SIZE 10M SEGMENT SPACE MANAGEMENT AUTO; 

CREATE FLASHBACK ARCHIVE archivetest TABLESPACE archivetest_tabspace QUOTA 50M RETENTION 7 DAY; 

ALTER TABLE table_name FLASHBACK ARCHIVE archivetest; 

SELECT * FROM table_name AS OF TIMESTAMP TO_TIMESTAMP ('2018-11-29 14:05:11', 'YYYY-MM-DD HH24:MI:SS');

Docker and node_modules

Development environment for a NodeJS App

Dockefile

FROM node:16-alpine

WORKDIR /app

COPY package.json ./

RUN npm install

COPY . .

EXPOSE 3000

CMD ["npm", "start"]

.dockerignore

node_modules
npm-debug.log
.git
Dockerfile
.dockerignore

Open your browser on http://localhost:3000

docker-compose.yaml

version: "3.8"

services:
  app:
    build:
      context: .
      dockerfile: Dockerfile
    volumes:
      - './src:/app/src'
      - './public/assets:/app/public/assets'
      - '/app/node_modules'
    ports:
      - 3000:3000
    stdin_open: true
    environment:
      - CHOKIDAR_USEPOLLING=true