Simon Willison (prominent tech blogger) recently highlighted an ingenious infrastructure solution from exe.dev, a new hosting provider focused on high-density virtual machine management. The service offers a compelling package for developers, providing up to 25 virtual machines (VMs) that share a hardware pool for a flat monthly fee. While the pricing is attractive, the real innovation lies in how the platform handles network routing through the Secure Shell (SSH) protocol. Unlike web traffic, which uses a "Host" header to tell a server which website a visitor wants, SSH lacks a built-in mechanism to distinguish between different destinations sharing the same entry point. To bypass this limitation, exe.dev avoids assigning a unique IP address to every single VM—a costly endeavor given the global shortage of IPv4 addresses. Instead, they ensure each user has an IP address unique to their specific account, even if that IP is shared with others. When a user connects, the system cross-references the incoming IP with the user's SSH public key (a cryptographic credential for secure login). This dual-layer identification allows their load balancer—a tool that directs network traffic—to pinpoint exactly which VM should receive the connection. This approach represents a sophisticated workaround for a long-standing protocol limitation. By leveraging public keys as unique identifiers, the service offers a seamless experience without the overhead of massive IP blocks. For those interested in system architecture, it serves as a masterclass in creative problem-solving within the constraints of legacy internet protocols, showing how modern infrastructure can find efficiency by rethinking the fundamentals of network identification.

Simon Willison (prominent tech blogger) recently highlighted an ingenious infrastructure solution from exe.dev, a new hosting provider focused on high-density virtual machine management. The service offers a compelling package for developers, providing up to 25 virtual machines (VMs) that share a hardware pool for a flat monthly fee. While the pricing is attractive, the real innovation lies in how the platform handles network routing through the Secure Shell (SSH) protocol. Unlike web traffic, which uses a "Host" header to tell a server which website a visitor wants, SSH lacks a built-in mechanism to distinguish between different destinations sharing the same entry point. To bypass this limitation, exe.dev avoids assigning a unique IP address to every single VM—a costly endeavor given the global shortage of IPv4 addresses. Instead, they ensure each user has an IP address unique to their specific account, even if that IP is shared with others. When a user connects, the system cross-references the incoming IP with the user's SSH public key (a cryptographic credential for secure login). This dual-layer identification allows their load balancer—a tool that directs network traffic—to pinpoint exactly which VM should receive the connection. This approach represents a sophisticated workaround for a long-standing protocol limitation. By leveraging public keys as unique identifiers, the service offers a seamless experience without the overhead of massive IP blocks. For those interested in system architecture, it serves as a masterclass in creative problem-solving within the constraints of legacy internet protocols, showing how modern infrastructure can find efficiency by rethinking the fundamentals of network identification.