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Reverse Proxy

It is occasionally necessary to run interactive software on Turing which is accessed via a web interface. This can be accomplished through the OpenOnDemand reverse proxy.

OpenOnDemand

Turing's Open OnDemand instance supports acting as a reverse proxy for things running on compute nodes. It has two simialar versions of the endpoint:

  • https://ondemand.turing.wpi.edu/node/<node>.cm.cluster/<port>
  • https://ondemand.turing.wpi.edu/rnode/<node>.cm.cluster/<port>

The difference between the two is that node passes the path through unchanged, while rnode strips off the excess path components.

Example

Pick a random port 

$ WEB_PORT=$(free_port $((10000+RANDOM%10000))) # (1)! (2)!
$ echo "Connect at https://ondemand.turing.wpi.edu/node/$HOSTNAME.cm.cluster/$WEB_PORT"
$ python serve.py $WEB_PORT
1. Pick a random port in the high part of the range. If you attempt to use a port that's already in use -- including by your own software, it will fail. By randomly choosing, you drastically reduces the chances of collision.

2. You can also use the free_port program provided by the wpi-scripts module. This will start with the provided one, and consecutively test ports until it finds an open one, returning that number.

from http.server import BaseHTTPRequestHandler, HTTPServer
import sys

class SimpleHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        self.send_response(200)
        self.end_headers()
        self.wfile.write(f"You queried path: {self.path}".encode())

if __name__ == '__main__':
    port = int(sys.argv[1])
    server = HTTPServer(('0.0.0.0', port), SimpleHandler)
    print(f"Serving on http://0.0.0.0:{port}")
    server.serve_forever()

In this example, if I then visit the site, it reports the connected path

# Connecting with node
- Visit https://ondemand.turing.wpi.edu/node/compute-2-02.cm.cluster/18623/gompei
- Returns "You queried path: /node/compute-2-02.cm.cluster/18623/gompei"
- Python logs 10.128.147.168 - - [28/Jul/2025 11:03:59] "GET /node/compute-2-02.cm.cluster/18623/gompei HTTP/1.1" 200 -

# Connecting via rnode
- Visit https://ondemand.turing.wpi.edu/rnode/compute-2-02.cm.cluster/18623/gompei
- Returns "You queried path: /gompei"
- Python logs 10.128.147.168 - - [28/Jul/2025 11:03:59] "GET /gompei HTTP/1.1" 200 -