A question about /ssh/revdial

[shiqinfeng1]

I'm a new user of ShellHub and I have a question. When an SSH client connects to a device, why doesn't it directly query the ConnectionManager cache to obtain the dialer, but instead let the agent initiate the /ssh/revdial?revdial.dialer=uID request to obtain the dialer through the uID?

[gustavosbarreto]

The reason the SSH client doesn’t directly access the ConnectionManager cache to get the dialer and instead relies on the agent to initiate the /ssh/revdial?revdial.dialer=uid is rooted in ShellHub’s architecture and its use of reverse tunneling over a persistent WebSocket control channel.

When a device connects to ShellHub, it establishes a persistent WebSocket connection to the server. This WebSocket isn’t used for data transfer in the actual SSH sessions — it acts more like a control channel, allowing the server to send commands or requests to the agent (such as asking it to initiate a new tunnel).

Whenever an SSH client initiates a connection, ShellHub generates a unique identifier (uid) for that session and stores it. Then, using the existing WebSocket connection, the server sends a message to the agent, instructing it to open a new connection to /ssh/revdial?revdial.dialer=uid. This creates a separate, dedicated tunnel for that specific SSH session.