Develop Reference

find available port to run server

What's the best approach in python to do something like what happens when you run jupyter notebook, in other words, run a server (for example, with http.server) on some available port if the default one isn't available? Is it common to just catch the error if starting the server fails and try a different port until it works?

You can use port 0 - this will bind your server to some port that is currently known to be available by kernel. However, that makes a problem of service discovery - how your clients will know which port number server is listening on? If that's only you, shouldn't be big deal.

How to port forward from Eclipse Che instance to local machine?

Background
So after about a year of having a GoDaddy cloud service, and super disappointed with it from the get-go. Once they announced that they would be discontinuing Cloud Server services, it was like a sign from the heavens.
I then created a Google Cloud account. One of the biggest reasons I got a Cloud Server to begin with was to have an eclipse Che instance, an IDE wherever you are! I love it, but despite the temporary partnership between Bitnami and GoDaddy, launching a Eclipse instance with them with such a mind-numbing task since their internal Factory build still required a ton of Docker configurations...
And though I can appreciate the fact that I did learn the ins-and-outs of configuring Dockers Network settings, which is not something to wince at... As soon as I got my Google Cloud account it was simply a 1 2 3 and go!
Question
Whilst I'm running an Eclipse chat instance, what is the proper way to port-forward a given work space to my local machine? The scenario is simple...
I created a Python stack of which I am using Django but when I run server, of course default being the local IP to the project, I have yet to find the easy and more than likely existing standard way to run the Django server and have the eclipse Che create the URL to the project. I'm ninety-nine percent sure that I'm going about this the wrong way given the fact that even some of the demo stack projects with Node or Python are plug-and-play.
PS: I am able to ssh into the workspace no issue, I'm just confused on how to port forward from remote to local as I've only really done it the other way around.. ssh -R ... or -L?

What you need is SSH Tunnel, which is -L. If you need to send a port from local to server that is called a Reverse SSH Tunnel, which is -R.
so simple command
ssh -L <localport>:127.0.0.1:<remoteport> <user>#<server>

Some extension to the other answer mentioning ssh tunneling...
If you run a docker-dev on a server (e.g. 192.168.1.123) not being your local machine in eclipse-che that provides some web service you want to access, then find out the IP address of the docker-dev, e.g. by opening a terminal in your eclipse che workspace and executing ip addr. There you will see some 172.17.x.x that is accessible only from the server. Assume the service in docker-dev is listening on port 12345, then you need the following ssh port forwarding from your local machine to access it:
ssh -L 8888:172.17.0.2:12345 192.168.1.123
While the ssh connection is open, you can access the web service with you browser by accessing http://127.0.0.1:8888/

Python process suspends on SSH logout after nohup/screen

I have a remote server through Blue Host that's intended to run a server based on Twisted for Python. The only access I have to it is over SSH, so to keep Python running after I log out I tried using nohup python server.py & and screen -dm python server.py, getting the same results for each. Everything works fine until I log out of SSH - even though Python is running in the background as expected, once I've logged out, my client can no longer communicate with the server. The strange part is that if I log back in over SSH and check the running processes with ps aux, I see Python running and my client can successfully communicate with the server again. Even if I don't type anything at all once I log back in, everything works as expected. But, of course, as soon as I log back out, it's as if the server is gone.
I've contacted support for the hosting service in case this is some oddity on their end, but hopefully this is something that can be resolved on my end instead.
Edit: Looks like Blue Host doesn't want me doing server-y stuff without buying the VPS upgrade so it looks like that's the big problem.
Edit 2: Okay, so in case anybody ends up having a similar problem, here's what the main issue turned out to be. I was mistaken in my original description; I was able to connect to the server but I was getting kicked off immediately for what turned out to be a MySQL error. I guess trying to connect to a localhost database with no active connection somehow causes problems, so instead I changed the MySQL connection command to connect to my site's IP address instead, even though it was the same IP as the server. That seemed to do the trick in terms of my main issue.

Don't use this method to keep the server process running. Instead try using supervisor (apt-get install supervisor). It allows you to daemonize your process, and ability to stop/restart etc.
Here's a sample config entry (/etc/supervisor/supervisord.conf):
[program:my_server]
command=python /path/to/server/server.py
directory=/path/to/server/
autostart=true
autorestart=true
stdout_logfile=/var/log/server.log
stderr_logfile=/var/log/server_error.log
user=your_linux_user_name
After you edit your config, do
sudo service supervisor stop
sudo service supervisor start #need to do this - doing a `restart` doesn't reload the config file!
your server should now be running properly. You can manage its lifecycle via sudo supervisorctl

google compute engine connection keeps disconecting

I have an instance on google compute engine, connecting to it by terminal: gcutil ssh, on it I have several DJango servieces. I run the server using: python manage.py runserver 0.0.0.0:8000. the services are being called from an iPhone application IOS 6.1
the problem I'm facing is that every few minutes (between 10- 15) I'm getting disconnected and have to reconnect and run the server again.
Why is my server being disconnected and how can I keep the it running?

Try using supervisor.d. It sounds like for what your trying to do, supervisor can keep your process up and running. http://supervisord.org/
Here's an example conf:
[program:app]
process_name = app-%(process_num)s
command =python /home/ubuntu/production/current/app/src/app.py --port=%(process_num)s
# Increase numprocs to run multiple processes on different ports.
# Note that the chat demo won't actually work in that configuration
# because it assumes all listeners are in one process.
numprocs = 4
numprocs_start = 8000
This is for running multiple processes of the same program. Just change around the args and it should work for you.

SSH normally times out after a period of inactivity, and that may be what is happening here. If so, this article might be useful to help configure SSH to send a regular message so connections are less likely to be dropped.
However, the core issue is that you'd like software you started at the terminal to keep running even when you're logged out. Consider using screen or tmux to host your shell sessions. This will allow your shell software to run even when you are not connected, and for you to pick up right where you left off when you reconnect. Here is a nice getting started post about tmux.
Once you're ready for production, take a look at the Django deployment docs.

Cannot access Python server running as Windows service

I have written a Python TCP/IP server for internal use, using win32serviceutil/py2exe to create a Windows service.
I installed it on a computer running Windows XP Pro SP3. However, I can't connect to it when it's running as a service. I can confirm that it's binding to the address/port, because I get a conflict when I try to bind to that address/port with another application. Further, I have checked the Windows Firewall settings and have added appropriate exceptions. If I run the server as a simple console application, everything works as expected. However, when I run it as a service, it doesn't work.
I vaguely remember running into this problem before, but for the life of me can't remember any of the details.
Suggestions, anyone?

Possibly the program may be terminated just after initialization. Please check whether it is continuously listening to the requests.
netstat -an |find /i "listening"
And analyze the command line parsed to the programs. You may use procexp to do that.

First of all, whenever you implement a Windows service, be sure to add proper logging.
My worker threads were terminating because of the exception, "The socket operation could not complete without blocking."
The solution was to simply call sock.setblocking(1) after accepting the connection.

Check to see that the service is running under the Nertwork Service account and not the Local System account. The later doesn't have network access and is the default user to run services under. You can check this by going to the services app under administrative tool in the start menu and looking for your service. If you right-click the service you can go to properties and change the user that it is run under.