What port must be open for Linux instances to enable remote control via Secure Shell (SSH)?

To enable remote control of Linux instances via Secure Shell (SSH), port 22 must be open. SSH is a protocol specifically designed for secure remote login and command execution over an insecure network. Port 22 is the default port designated for SSH connections, facilitating the encrypted transfer of information between a client and a server. By opening this port in the firewall settings of a Linux instance, you allow SSH clients to connect securely.

The other ports listed are associated with different services: port 21 is used for File Transfer Protocol (FTP), which is not secure; port 80 is the standard port for Hypertext Transfer Protocol (HTTP), used for web traffic but does not provide secure connections; and port 443 is primarily used for Hypertext Transfer Protocol Secure (HTTPS), which is for secure web traffic. Thus, for remote access to Linux instances using SSH, ensuring that port 22 is open is essential for proper functionality.