GoKawiilWe have a challenge with ssh. Every VM has a standard URL that we use for both HTTPS and SSH, e.g. undefined-behavior.exe.xyz . Just as you can type the domain into a web browser (and have TLS and auth taken care of for you), you can run:
ssh undefined-behavior.exe.xyz
To get a shell in your VM.
This is very straightforward to implement if you give each machine its own IP address, but exe.dev gives you many VMs on a flat rate subscription.
We cannot issue an IPv4 address to each machine without blowing out the cost of the subscription. We cannot use IPv6-only as that means some of the internet cannot reach the VM over the web. That means we have to share IPv4 addresses between VMs.
For the web, this is a long-solved problem. Many sites can and do have the same IP address. Web browsers send the domain they used to reach the server in the HTTP request as the Host header. The exe.dev proxy switches on this header and send requests to the appropriate VM.
SSH, on the other hand, has no equivalent of a Host header. If we reuse IPv4 addresses between VMs, we have no way to send SSH connections to the right VM.
How we solved this: SSH IP sharing
Instead of using one IP address for all VMs, we have a pool of public IPv4 addresses. Each VM is assigned a unique address relative to its owner.
So instead of an A record, you will find
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