[Fullstack] Learning note for Fullstack developer - FrontendMaster

Command Line

1. Navigate to your home directory

cd ~

2. Make a directory call "temp"

mkdir temp

3. Move into temp

cd temp

4. List the idrectory contents

ls -la temp

5. Make a file called "hello"

touch hello

6. List the directory contents

ls -la temp

7. Move out of temp

cd ../

8. Delet temp

rm -rf temp

9. Using man to get help for `rm`

man rm

Search for flag

/ -r

 

Secuirty

Hashing: with just hashing, you can reverse the hash

openssl md5 foo

openssl sha1 foo

openssl sha256 foo

Hashing + salt: with hash + salt, it's really difficult to reverse it

 

 

 

 

 

VIM

• insert mode: i
• normal mode: ESC
• command mode: :, for example, save and exit :wq
  
  • Exit and don't save:q!

 

Shell

• ~/.zshrc
• ~/.bash_profile

echo $0: tell which shell you are using

echo $USER

 

Server

Buying a VPS

https://www.digitalocean.com/

 

SSH into your remote server

// ssh into your server
ssh root@<your_IP>

// ssh into your server with private key
ssh -i ~/.ssh/fsfe root@<your_IP>

// Exit your server
exit

 

Modify ssh config:

# inside your .ssh folder
vi ~/.ssh/config

Host *
  AddKeysToAgent yes
  UseKeychain yes

ssh-add --apple-use-ketchain <name_of_ssh_private_key>

Now you should be able to ssh into remote server by omit to speicifing the key:

ssh root@<public_ip_address>

 

The Internet

# Check status of a network host
ping google.com
# Follow the path of your request
traceroute google.com
# Show network status
netstat -lt | less

 

DNS

# Lookup the nameservers for an domain
nslookup frontendmasters.com
# Lookup the DNS records for a domain
dig frontendmasters.com

 

Server

SSH into your server:

ssh root@<IP_ADDRESSS>

Update the server:

apt update

apt upgrade

Restart the server:

shutdown now -r

 

Create a user

1. Create a new user

adduser <YOU_NAME>

2. Add user to "sudo" group

usermod -aG sudo <YOU_NAME>

3. Switch User

su <YOU_NAME>

4. Check sudo access

sudo cat /var/log/auth.log

 

Enable login as new user

1. Create authorized_keys file

mkdir .ssh

cd .ssh/

vi authorized_key

2. Paste your SSH public key

3. Exit: you need to exit twice

exit

exit

4. Login with new user

ssh <YOU_NAME>@<IP_ADDRESS>

 

File Permissions

1. Change file permission

sudo cat /var/log/auth.log  # check the auth log for any actions

chmod 644 ~/.ssh/authorized_keys # -rw-rw-r--

2. Disable root login

sudo vi /etc/ssh/sshd_config

Change to PermitRootLogin no

Save and quite

3. Restart ssh daemon

sudo service sshd restart

Now the root login should be disabled.

 

Server

1. Install nginx

sudo apt install nginx

2. Start nginx

sudo service nginx start

3. Navigate to your server in the browser

 

View default nginx configuration

less /etc/nginx/sites-available/default

 

Defautl value locates:

/var/www/html/

 

Install tooling

1. Link to newest node.js source

curl https://deb.nodesource.com/setup_19.x | sudo -E bash -

2. Install node.js

sudo apt-get install nodejs

3. Install git

sudo apt install git

 

Application setup

1. Chnage ownership of /www

cd /var/www

sudo chown -R $USER:$USER /var/www  # no need to sudo everytime

2. Make an application directory

mkdir /var/www/app

cd app

3. Initialize empty git repo in /app

git init

4. Start your application

npm init -y

let app listen on prot 3000

 

Proxy pass

Connect nginx to our web server

1. Create a new nginx server and proxy requests

sudo vi /etc/nginx/sites-enabled/mycompany

server {
  listen 80 default_server;
  listen [::]:80 default_server;
  
  root /var/www/html;
  index index.html;
  
  server_name <your_domain>;
  
  location / {
    proxy_pass http://127.0.0.1:3000/;
  }
}

2. Point nginx to new server

sudo vi /etc/nginx/nginx.conf

##
# Virtual Host Configus
##

- include /etc/nginx/sites-enabled/*;
+ include /etc/nginx/sites-enabled/<YOUR_COMPANY>;

3. Double check configuration is working

sudo nginx -t

 4. Restart nginx server

sudo service nginx restart

 

PM 2

1. Install PM 2

sudo npm i -g pm2

2. Start PM2

pm2 start app.js --watch

3. Setup auto restart

pm2 list

pm2 save

pm2 startup

 

Git

1. Ensure git uses your new ssh key

vi ~/.ssh/config

Host github.com
 Hostname github.com
 IdentityFile ~/.ssh/gh_key

2. Change permission of config to 600

cmod 600 ~/.ssh/config

3. Change permission of gh_key to 600

chmod 600 ~/.ssh/gh_key

 

In case you get stuck

Stop a running process

pkill <process>

Test your ssh connection

ssh -vT git@github.com

Save a readonly file in vim

:w !sudo tee %

View permissions as numbers

stat -c %a <file_name>

 

Seucirty

check the well known prots

less /etc/services

 

nmap

1. Install nmap

sudo apt install nmap

2. Run nmap

nmap <your_service_ip>

3. Extra service/version information

nmap -sV <your_server_ip>

Port 3000 is open by Node.js, but we don't want it open. NGINX handle the connection.

 

Firewall

ufw - uncomplicated firewall

ufw <allow|deny|reject> <http|https|ssh>

1. Check firewall status

sudo ufw status

2. Allow SSH & http

sudo ufw allow ssh

sudo ufw allow http

3. Enable firewall

sudo ufw enable

 

Permission

https://quickref.me/chmod

 

Application Updates

1. Instal unattended upgrades

sudo apt install unattended-upgrades

2. Enabled upgrades

sudo dpkg-reconfigure --poriority=low unattended-upgrades

 

Create a cron job

crontab -e

*/2 * * * * sh /var/www/app/github.sh 2>&1 | logger -t github.sh

# github.sh
#! /sur/bin/bash
cd /var/www/app/
git pull origin main --ff-only

 

Logs

• tail: Output the last part of a file
• head: Output the first part of a file
• less: Output one page at time
• cat: Output entire file

Example: follow the output of a file

tail -f 

Normally on server, we have

• syslog
• auth.log
• nginx/access.log

 

Redirection

• | : read from stdout
• > : write stdout to file
• >> : append stdout to file
• < : read from stdin
• 2>&1 : redirect both stderr and stdout

 

Finding things

• find : search file names

1. Find all log files in /var/log

find /var/log -type f -name "*.log"

You might get permission issue

sudo !!

Wil help to run last cammnd with sudo

2. Find all directories with the name log

sudo find / -type d -name log

• grep: search file contents

zgrep FILE : search inside gzip file

FInd running node processes

ps aux | grep node

Nginx redirection

// redirect /help to https://developer.mozilla.org/en-US/

location /help {
   return 301 https://developer.mozilla.org/en-US/
}

 

Gzip

 

Subdomain

vi /etc/nginx/sites-enabled/blog.<YOUR_COMPANY>

server {
    listen 80;
    listen [::]:80;
    server_name blog.<your_domian>;
    
    location / {
        proxy_pass http://localhost:3000;
    }
}

 

sudo vi /etc/nginx/nginx.conf

include /etc/nginx/sites/enabled/blog.<YOUR-COMPANY>;

sudo service nginx restart

sudo nginx -t

 

WebSockets

vi /etc/nginx/site-enabled/<YOU_COMPANY>

location / {
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Cpnnection "upgrade";
    
    proxy_pass http://127.0.0.1:3000;
}

check the configuration

sudo nginx -t

restart nginx

sudo service nginx restart

 

Database

SQLITE 3

1. Install sqlite 3

npm install sqlite3

2. Setup a database

1. Create a table name "vistors"
2. Create a column named "count"
3. Create a column named "time"

3. On connection, save current visitor count

const sqlite = rquire('split3')
const db = new sqlite.Database(":memory:")

db.serialize(() => {
    db.run(`
        CREATE TABLE IF NOT EXISTS visitors (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            count INTEGER,
            time TEXT
        )
    `)
})

function getCounts() {
    db.each("SELECT * FROM visitors", (err, row) => {
        console.log(row)
    })
}

function shutdownDB() {
    getCounts()
    wss.clients.forEach((client) => {
        client.close()
    })
    console.log("Closing DB")
    db.close()
}

// express server
process.on('SIGINT', () => {
    server.close(() => {
        shutdownDB()
    })
})

// add data to the table
db.run("INSERT INTO visitors (count, time) VALUES (1, datetime('now'))")

 

HTTPS

Certbot: https://certbot.eff.org/instructions?ws=nginx&os=osx

For http2:

Modify the nginx config file to add http2

Container

Dockerfile:

FROM node:19-apline3.16
RUN mkdir -p /home/node/app/node_modules && chown -R node:node /home/node/app
WORKDIR /home/node/app

COPY --chown=node:node package*.json ./
USER node
RUN npm install

COPY --chown=node . .
EXPOSE 3000
CMD ["node", "app.js"]

Build docker container:

sudo docker build -t node-fsfe .

 Run:

docker run -d -p 3000:3000 node-fsfe

 

Load balancer

sudo vi /etc/nginx/nginx.conf

...
http {
  upstream nodebackend {
    server localhost:3000;
    server localhost:3001;
  }
  log_foramt upstreamlog '[$time_local] $remote_addr - $remoate_user - $server_name $host to: $upstream_attr: $request $status upstream_response_time $upstream_response_time msec $msec request_time $request_time';
  ...
}

 

sudo vi /etc/nginx/sites-enabled/<YOUR_COMPANY>

access_log /var/log/nginx/access.log upstreamlog;
location / {
  ...
  proxy_pass http://nodebackend;
}

sudo nginx -t

sudo service nginx restart

sudo service nginx restart

 Check the logs:

sudo tail - /var/log/nginx/access.log