What does Dockerfile define?

Great question! Think of a Dockerfile as a blueprint or a recipe for creating a virtual computer environment (called a "container").

In this specific lab, the Dockerfile you are creating defines exactly how our SSH server should look and behave. Here’s a breakdown of what it defines:

The Base Operating System: FROM ubuntu:22.04 tells Docker to start with a clean Ubuntu Linux environment.
Software Installation: It specifies which programs to install. In this case, we are installing openssh-server (to allow remote logins) and nginx (a web server).
User Setup: It creates a specific user named sshuser and sets a password (password123). This simulates a real user on a remote server.
Security Configurations: It sets up the SSH rules, such as permitting password authentication and public key authentication, while disabling root login for better security.
Environment Settings: It creates necessary folders (like .ssh) and sets the correct permissions so that security keys will work later.
Network Ports: EXPOSE 22 80 tells Docker which "doors" (ports) to leave open for communication.
The Startup Command: CMD ["/usr/sbin/sshd", "-D"] defines the main task of the container—to keep the SSH service running in the background.

Why do we use it?
Instead of manually setting up a server every time, the Dockerfile allows us to build the exact same environment automatically every time we run the docker build command.

Ready to build your image? Just run:

sudo docker build -t ssh-server .