Common Mistakes I See Students Make

By Ravindra Bagale Last updated: 25 September 2026

Hard-coding passwords in code and pushing to GitHub. Use .env files with permission 600 and add them to .gitignore.
Using localhost in Node.js and getting ECONNREFUSED ::1:3306. Use 127.0.0.1.
Running the app with node app.js in the SSH session and closing the terminal — the app dies. Use pm2 or systemd.
Running both pm2 and a systemd unit for the same app → port 3000 already in use.
Opening port 3306 or 3000 to the internet instead of using the reverse proxy.
Forgetting setsebool -P httpd_can_network_connect 1 on CentOS → 502 Bad Gateway.
Not restarting PHP-FPM/Apache after installing PHP modules.