Every server in this book is administered over SSH, the Secure Shell: it gives you a shell on a machine you cannot touch, copies your code to it, and tunnels database traffic so that port 3306 never faces the internet. Nearly everyone runs OpenSSH 23,707 , from the OpenBSD 11,943 project. Upstream is at 10.5 (11 August 2026), Ubuntu 26.04 225 LTS ships 10.2p1 with fixes backported, and Windows 11 bundles an OpenSSH client as ssh.exe.
The examples run on the WSL2 6 machine from A Local Stack with openssh-server installed. A throwaway account, bk3ssh, plays the remote user, so the host is localhost; on a real server only the name changes. Key Pairs and SSH Access applies the same ideas to EC2 24 .