alyxruntime

Use any other computer's CPU/GPU as your Jupyter runtime - like Colab's "connect to local runtime", but for any machine you control, from the command line or from Python.

 your laptop        Cloudflare edge            GPU box (host) - no open ports, outbound only
 ┌────────────┐ https ┌───────────────┐ tunnel ┌─────────────────────────────────────────┐
 │ alyxruntime│ ────► │ *.trycloudflare│ ◄──────│ cloudflared ─► IP-allowlist gate        │
 │  connect   │ +token│     .com       │        │                  └─► Jupyter (loopback) │
 └────────────┘       └───────────────┘        │                        └─► kernel (GPU) │
                                                └─────────────────────────────────────────┘

The host talks out to Cloudflare through cloudflared, so there is no port forwarding, no public IP, and HTTPS is included - it works from behind home routers, NAT and most firewalls.

Install

pip install "alyxruntime[host]"   # on the machine that SHARES its GPU/CPU
pip install alyxruntime           # on the machine that CONNECTS (lighter)

Usage

On the host (the machine with the GPU):

alyxruntime stream --allowed_ip 203.0.113.7                # your client's public IP
alyxruntime stream --allowed_ip 203.0.113.7 10.0.0.0/24    # several IPs / CIDR ranges
alyxruntime stream --allowed_ip all                        # any IP - the token is the only gate

It starts a Cloudflare quick tunnel (if cloudflared is missing it offers to download the official binary, or pass --install-cloudflared) and prints a ready-to-paste command with a random access token:

alyxruntime connect 'https://random-words.trycloudflare.com/?token=...'

Not sure what your public IP is? Run alyxruntime connect from the client anyway: the host replies access denied for IP x.x.x.x. Ask the host to add it with --allowed_ip x.x.x.x.

On the client:

alyxruntime connect https://my-host:8765/?token=XXXX   # verifies, shows remote CPU/RAM/GPU, saves session
alyxruntime run train.py            # run a script   (also .ipynb, `-c "code"`, or stdin with `-`)
alyxruntime shell                   # interactive prompt; variables persist between commands
alyxruntime info                    # remote CPU / RAM / GPU
alyxruntime upload data.csv         # copy files to the host's working dir
alyxruntime download model.pt
alyxruntime restart                 # fresh kernel
alyxruntime disconnect --kill-kernel

Plots (plt.show()) are saved locally to ./alyx_outputs/. VS Code / JupyterLab also work: Select Kernel -> Existing Jupyter Server -> paste the same URL.

From Python

from alyxruntime import Runtime

rt = Runtime.connect("https://my-host:8765/?token=XXXX")
rt.run("import torch; print(torch.cuda.is_available())")
res = rt.run("2 + 2", echo=False);  print(res.results)     # ['4']
rt.upload("data.csv"); rt.download("out.pt")

Host side from Python: from alyxruntime import serve; serve(allowed_ip=["203.0.113.7"]).

Stable URL (named tunnel)

Quick tunnels get a new random URL every run. For a fixed hostname, create a tunnel in the Cloudflare dashboard (Zero Trust -> Networks -> Tunnels), point a public hostname at http://localhost:9000, then:

alyxruntime stream --tunnel-token <TOKEN> --public-url https://gpu.example.com --port 9000 \
                   --allowed_ip 203.0.113.7

stream options

Security - please read

A runtime is remote code execution by design: whoever connects runs arbitrary code as the host user.

• Two independent gates: the IP allowlist and a random token.
• How the allowlist works with a tunnel: cloudflared reaches the host from 127.0.0.1, so the socket address is useless for filtering. The gate instead reads the CF-Connecting-IP header, which Cloudflare's edge sets itself, and checks every request against --allowed_ip. Requests with no such header (anything not coming through the tunnel) are refused, loopback gets no special pass, and each request is forced to Connection: close so one vetted connection can't be reused by someone else.
• The quick-tunnel URL is public: anyone who learns it can reach the gate (and be refused). Treat the token like a password, and don't paste the connect line in public places.
• Traffic passes through Cloudflare's network (TLS to Cloudflare, then Cloudflare -> your host over the tunnel); Cloudflare can technically see it. If that's unacceptable, use --no-tunnel with your own VPN.
• IP allowlisting trusts that Cloudflare reports the true client IP. It won't protect against someone sharing your NAT/VPN exit IP, and mobile/CGNAT or rotating-IP connections will need a CIDR range.
• Local users on the host can reach the gate on its loopback port and are trusted like the host user.
• Don't run stream as root unless you mean it. The client's saved token lives in ~/.alyxruntime/session.json (0600).
• Cloudflare's free quick tunnels are meant for development: no uptime guarantee, and you should read Cloudflare's terms before using them for anything heavy or long-lived (use a named tunnel for that).