Multi-hop ssh Connections

Posted by Ryan Himmelwright on Sun, Jun 27, 2021
Tags linux, ssh, network, shell
Karsh Alumni Center (Duke University), Durham NC

Last weekend, I wanted to ensure that I could work on a personal project using my typical setup, while I was away for a few hours. This consists of running VS Code on my macbook air, but remotely connected to my Linux desktop. All of the coding actually happens on the Linux computer, even though I am running VS code on my macbook. However, when outside of my home network, connecting to the desktop requires multiple ssh hops. Fortunately, configuring ssh to handle a multi-hop setup is actually quite easy and…. it works with the VSCode remote plugin. Here’s how.

Problem

To restate the problem: If I am outside of my home network, I need to make multiple sshhops’ in order to get to my desktop (charmeleon).

Laptop -> Ponyta (SSH Entry Node) -> Charmeleon (Desktop)

Normally, this requires me to first ssh into my home network (ponyta), and then from there, ssh again to whichever device I want to connect to (In this example, Charmeleon). Out of pure laziness, I want to run these steps as a single command. Additionally, for tasks that are automated, or outside of a shell, connecting to my desktop truly needs to be a single step in order to work.

Solution

An simple solution is to create a new host item in the ssh config file. In this file, we can utilize the ProxyCommand option to setup a multi-hop scenario. So, I added the following my ~/.ssh/config (make sure to swap out your PORT and HOSTNAME values accordingly):

Host remote-charmeleon
	Hostname CHAMELEON-IP
	User ryan
	ProxyCommand ssh -p PORT ryan@PUBLIC_FACING_PONYTA_HOSTNAME -W %h:%p

Now, I only need to run ssh remote-charmeleon to kick off the the full Laptop -> (Ponyta) -> Charmeleon sequence. Easy.

Setting it up in VSCode

Connecting via a multi-hop ssh connection in vscode
Connecting to a multi-hop system via ssh in VS Code

Now, how can this be used in a VS Code session?

All I had to do was add the config sequence to the ssh config file that VSCode uses, which I usually have set to be different from my default one.

To do this, call the Remote-SSH: Open SSH Configuration File in VS Code to open the proper config file. Next, add the same code from above to the config. From then on, you can select that host item when running Remote-SSH: Connect to Host... in VS Code.

For example, I can now select remote-charmeleon when VSCode prompts for the host to connect to.

Conclusion

That’s all. It’s a simple solution that I very much appreciate. I always forget how powerful ssh is, especially when you start setting up custom configs. It’s worth taking a look at! As always, man ssh is a great place to start 😉.

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