Interview Questions

By Ravindra Bagale Last updated: 25 September 2026

Q1. What is PHP-FPM?: FastCGI Process Manager — a separate service that runs PHP worker processes; Nginx (or Apache) passes .php requests to it over a unix socket or TCP.
Q2. Why do we run Gunicorn in front of a Flask app?: Flask's built-in server is for development only. Gunicorn is a production WSGI server that runs multiple worker processes reliably; Nginx sits in front for TLS and static files.
Q3. What is pm2 used for?: A process manager for Node.js that keeps apps running, restarts them on crash, starts them at boot (pm2 startup + pm2 save), manages logs and supports cluster mode.
Q4. Why should the database never be exposed to the internet?: Open database ports are scanned and attacked constantly (brute force, ransomware). The DB should listen on localhost or a private subnet and allow access only from the app's security group.
Q5. How do you create a MySQL user with access to only one database?: CREATE USER 'app'@'localhost' IDENTIFIED BY '...'; GRANT ALL PRIVILEGES ON appdb.* TO 'app'@'localhost'; FLUSH PRIVILEGES;
Q6. What causes a 502 Bad Gateway error behind Nginx?: The upstream is unreachable: app not running, wrong port/socket in proxy_pass/fastcgi_pass, app crashed, or SELinux blocking the connection.
Q7. How do you run an application as a service on Linux?: Create a systemd unit file in /etc/systemd/system/, then sudo systemctl daemon-reload, sudo service <name> start and sudo systemctl enable <name>.