Ubuntu-latest GitHub runner cannot Connect to localhost API

What specifically needs to be changed in the below in order for a program running on an Ubuntu-latest GitHub runner to successfully connect to a Twisted web server running on localhost of the same GitHub runner? The same code works on a Windows laptop, with only minor changes like using where twistd on Windows versus which twistd on Ubuntu as shown below. **SOME RELEVANT CODE:** The code to start the Twisted web server on localhost is in a script called twistdStartup.py that reads as follows: import subprocess import re import os escape_chars = re.compile(r'\x1B\[[0-?]*[ -/]*[@-~]') def runShellCommand(commandToRun, numLines=999): proc = subprocess.Popen( commandToRun,cwd=None, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, shell=True) while True: line = proc.stdout.readline() if line: if numLines == 1: return escape_chars.sub('', line.decode('utf-8').rstrip('\r|\n')) else: print(escape_chars.sub('', line.decode('utf-8').rstrip('\r|\n'))) else: break print("About to create venv.") runShellCommand("python3 -m venv venv") print("About to activate venv.") runShellCommand("source venv/bin/activate") print("About to install flask.") runShellCommand("pip install Flask") print("About to install requests.") runShellCommand("pip install requests") print("About to install twisted.") runShellCommand("pip install Twisted") ##Set environ variable for the API os.environ['PYTHONPATH'] = '.' print("Done updating PYTHONPATH. About to start server.") twistdLocation = runShellCommand("which twistd", 1) startTwistdCommand = twistdLocation+" web --wsgi myAPI.app &>/dev/null & " print("startTwistdCommand is: ", startTwistdCommand) subprocess.call(startTwistdCommand, shell=True) print("startTwistdCommand should be running in the background now.") The code in a calling program named startTheAPI.py that invokes the above twistdStartup.py is: myScript = 'twistdStartup.py' print("About to start Twisted.") subprocess.Popen(["python", myScript], stdout=subprocess.PIPE, stderr=subprocess.STDOUT) print("Just finished starting Twisted.") The logs produced by that step in the GitHub Action job are as follows: About to start Twisted. Just finished starting Twisted. The results of running the curl command on the same Ubuntu-latest GitHub runner in the next step of the same job after waiting 30 seconds for startup are as follows: $ curl http://localhost:1234/api/endpoint/ % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 curl: (7) Failed to connect to localhost port 1234 after 1 ms: Connection refused The contents of a callTheAPI.py program that runs the curl command would look like: import subprocess import re import os escape_chars = re.compile(r'\x1B\[[0-?]*[ -/]*[@-~]') def runShellCommand(commandToRun, numLines=999): proc = subprocess.Popen( commandToRun,cwd=None, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, shell=True) while True: line = proc.stdout.readline() if line: if numLines == 1: return escape_chars.sub('', line.decode('utf-8').rstrip('\r|\n')) else: print(escape_chars.sub('', line.decode('utf-8').rstrip('\r|\n'))) else: break print("About to call API.") runShellCommand("curl http://localhost:1234/api/endpoint/") print("Done calling API.") **SUMMARY:** The twistdStartup.py script is running, but is failing to provide any output to the logs despite all the print() commands. The curl command fails to connect to the correctly-stated http://localhost:1234/api/endpoint/