SSH tunneling to connect to remote computers

We present software to establish secure shell (command prompt) connections to remote computers to perform maintenance, configuration, or debugging, even when the remote computers are connected to the Internet such that incoming connections are not allowed. The software is easy to install and to operate, has few dependencies, provides many useful security guarantees, and scales to large number of remote computers, possibly partitioned into isolated groups. The software relies on one or two inexpensive cloud services. A preliminary version of the system has been used for nine years to access geographically-remote computers that serve as sensors in wildlife tracking systems.