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Intermediate9 lessons220 minutes

Firewall and hardening

Close what has no business being open, slow automated attacks down, and check regularly what the server exposes — without locking yourself out.

A server on the internet receives connection attempts continuously. This course reduces the attack surface with ufw and fail2ban, then sets up the periodic verification that matters more than the initial installation.

What you will be able to do

  • Configure ufw as default-deny without losing your SSH access
  • Understand why Docker bypasses ufw, and what that means
  • Ban repeated attempts with fail2ban, and unban yourself
  • Know what a server actually exposes, and check it periodically

Before this course

Taken from the learning path this course belongs to: the course placed just before it. A suggested order, not a lock — nothing here closes until you have finished it.

Outline

  1. 01

    The firewall

    Deny by default, allow deliberately — and do not saw off the branch.

  2. 02

    Knowing what the machine exposes

    The periodic check, which matters more than the initial configuration.

Technical content last reviewed on 3 August 2026