DigitalOcean Cheatsheet

Building Node.js Application

To build Node.js without interrupting run below command:

nohup yarn build &

Install Node.js

cd ~
curl -sL https://deb.nodesource.com/setup_20.x -o /tmp/nodesource_setup.sh

Check and validate script file using command:

nano /tmp/nodesource_setup.sh

Install using commands:

sudo bash /tmp/nodesource_setup.sh

sudo apt-get install -y nodejs

To install yarn package manager use:

curl -sL https://dl.yarnpkg.com/debian/pubkey.gpg | gpg --dearmor | sudo tee /usr/share/keyrings/yarnkey.gpg >/dev/null
echo "deb [signed-by=/usr/share/keyrings/yarnkey.gpg] https://dl.yarnpkg.com/debian stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
sudo apt-get update && sudo apt-get install yarn

Verify installation using command:

node -v

Installing PostgreSQL

sudo apt update

sudo apt install postgresql postgresql-contrib

sudo systemctl start postgresql.service

To open postgreql in terminal use command:

sudo -i -u postgres
psql -h localhost -U postgres

Set postgres user password using below SQL:

ALTER USER postgres WITH PASSWORD 'postgres';

Check port on which server is running use SQL:

SELECT * FROM pg_settings WHERE name = 'port';

Create database using SQL:

create database todoapp;

Login to database (username: postgres):

psql -h localhost -U postgres

Running Node.js app in background with pm2

Install pm2 using below command:

yarn global add pm2

sudo npm install pm2@latest -g

Switch to your Node.js application directory and build your project using command like:

npm run build

yarn build

Run below command to run start script:

pm2 start npm --name "nextapp" -- start

Check status of running app process using command:

pm2 status

Stop process using command:

pm2 stop nextapp

To update app, rebuild application and restart process using command:

pm2 restart nextapp

To list running processes use command:

pm2 ls

Hosting Node.js (under pm2) with Nginx

Install Nginx using command:

sudo apt-get update
sudo apt-get install nginx

Setup your site by editing file:

sudo vim /etc/nginx/sites-available/default

Paste below config in file (change 3000 port with your node.js application port):

server {
        listen 80;
        server_name example.com www.example.com;
        root /var/www/html;
        index index.html index.htm;

        location / {
                proxy_pass             http://127.0.0.1:3000;
                proxy_read_timeout     60;
                proxy_connect_timeout  60;
                proxy_redirect         off;

                # Allow the use of websockets
                proxy_http_version 1.1;
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection 'upgrade';
                proxy_set_header Host $host;
                proxy_cache_bypass $http_upgrade;
        }
}

Restart nginx using command:

sudo service nginx restart

Copy local files to server using SSH

 scp -r full_path_of_source_folder username@server_ip:~/path_to_files/

Example:

 scp -r C:/Users/username/Documents/bedrock root@server_ip:~/bedrock/

Destination path should be a valid existing path.

Fix `npm install` getting killed

Run below command in ssh terminal:

sudo fallocate -l 1G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
sudo swapon --show
sudo cp /etc/fstab /etc/fstab.bak
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab
sudo sysctl vm.swappiness=10
echo 'vm.swappiness=10' | sudo tee -a /etc/sysctl.conf
sudo sysctl vm.vfs_cache_pressure=50
echo 'vm.vfs_cache_pressure=50' | sudo tee -a /etc/sysctl.conf

Kill process

Run below command in ssh terminal:

To list running process:

ps -aux

To kill by process ID

sudo kill <pid>

Or to kill process by name

sudo killall <process-name>

List process running on a port

sudo lsof -n -i :PORT_NUMBER | grep LISTEN

Create new user

adduser username
usermod -aG sudo username

Use password login:

Go to dashboard -> project -> access. Enter username and launch console. Type below command:

sudo nano /etc/ssh/sshd_config
sudo service ssh restart

change PasswordAuthentication from no to yes save

Deleting user

deluser username

Delete user with it's home:

deluser --remove-home userame

Run Python Jupyter Server

If python pip command is not installed use below command:

sudo apt install -y python3-pip

Installing jupyter using below command:

python3 -m pip install jupyter

To access jupyter you need to use SSH tunneling. Run below command in your local computer:

ssh username@server_ip -L 8888:localhost:8888 -t "jupyter notebook --no-browser --port 8888"

If you are using root user then use below command:

ssh [email protected] -L 8888:localhost:8888 -t "jupyter notebook --no-browser --port 8888 --allow-root"

Open http://localhost:8888/ in your browser. It will ask for login token, copy from console and paste.

Second method [prevents killing of server]

Instead of running above ssh command run below command:

 ssh -N -f -L 8888:localhost:8888 username@server_ip

This command will run a background port forwarding using ssh.

Now open digitalocean dashboard and go to your project. Click on: Access. Now enter your username and Launch Droplet console. Run below command under the terminal:

jupyter notebook

Open http://localhost:8888/ in your browser. It will ask for login token, copy from console and paste.

Using jupyter in virtual environment:

Install python virtual environment:

sudo apt install -y python3-venv

Setup path for environments:

mkdir environments
cd environments

Create environment:

python3 -m venv my_env

Check if environment created:

ls my_env

Activating environment:

source my_env/bin/activate

To leave the environment, type the command deactivate and you will return to your original directory.

Install jupyter kernel for virtual environment

ipython kernel install --user --name=my_env

Now when you run the jupyter notebook you will be able to select the kernel to run in virtual environment.

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