I use IDEA 10.5 for my Flask experimentation. Flask has en embedded test server (like Django does)
When I launch my test class, the dev server launches as well on port 5000. All good.
* Running on http://127.0.0.1:5000/
When I click on the "Stop process" button (red square), I get the message saying the process is finished :
Process finished with exit code 143
However the server is still alive (responds to requests) and I can see I still have a python process running.
Obviously this prevents me from relaunching the test straight away, I have to kill the server process first.
How do you manage to get both your program and the server ending at the same time ?
I guess what happens is that you start your flask app which then is forking the development server as a new process. If you stop the app the forked process is still running.
This looks like a problem, that cannot easily be solved within the means of your IDE. You could add something to your main to kill the already running server process, before starting the app again, but that seems ugly.
But why don't you just start your app with app.run(debug=True) as described in flask doc? The server will reload automatically everytime you changed your app so you don't have to stop and restart it manually.
EDIT:
Something a bit quirky just came to my mind: if you just need a comfortable way to kill the server from within the IDE all you have to do is to introduce a syntactical error in one of the places the reloader monitors, save the file and the server will choke on it and die :)
This doesn't happen anymore with newer versions (tested with PyCharm 2.0)
Related
I have a Flask app that I run with uWSGI. I have configured logging to file in the Python/Flask application, so on service start it logs that the application has been started.
I want to be able to do this when the service stops as well, but I don't know how to implement it.
For example, if I run the uwsgi app in console, and then interrupt it with Ctrl-C, I get only uwsgi logs ("Goodbye to uwsgi" etc) in console, but no logs from the stopped python application. Not sure how to do this.
I would be glad if someone advised on possible solutions.
Edit:
I've tried to use Python's atexit module, but the function that I registered to run on exit is executed not one time, but 4 times (which is the number of uWSGI workers).
There is no "stop" event in WSGI, so there is no way to detect when the application stops, only when the server / worker stops.
I created a droplet that runs a flask application. My question is when I ssh into the droplet and restart the apache2 server, do I have to keep the console open all the time (that is I should not shut down my computer) for the application to be live?
What if I have a dynamic application that runs scripts in the background, do I have to keep the console open all the time for the dynamic parts to work?
P.S:
there's a similar question in SO about a NodeJs app but some parts of the answer they provided are irrelevant to my Flask app.
You can use the "screen" command to mantain the sesion open.
please see https://www.rackaid.com/blog/linux-screen-tutorial-and-how-to/
In my opinion it is not a good practice to use remote computers for the development stage unless you don't have an other option. If you want to make your application available after logging out from the ssh console, screen works, but it still a workaround.
I would suggest taking a look at this great tutorial on how to daemonize flask applications with Gunicorn+Nginx.
You needn't keep the console on, the app will still running after you close the console on your computer. But you may need to set a log to monitor it.
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.
I'm coming from PHP/Apache world where running an application is super easy. Whenever PHP application crashes Apache process running that request will stop but server will be still ruining happily and respond to other clients. Is there a way to have Python application work in a smilar way. How would I setup wsgi server like Tornado or CherryPy so it will work similarly? also, how would I run several applications from one server with different domains?
What you are after would possibly happen anyway for WSGI severs. This is because any Python exception only affects the current request and the framework or WSGI server would catch the exception, log it and translate it to a HTTP 500 status page. The application would still be in memory and would continue to handle future requests.
What we get down to is what exactly you mean by 'crashes Apache process'.
It would be rare for your code to crash, as in cause the process to completely exit due to a core dump, the whole process. So are you being confused in your terminology in equating an application language level error to a full process crash.
Even if you did find a way to crash a process, Apache/mod_wsgi handles that okay and the process will be replaced. The Gunicorn WSGI server will also do that. CherryPy will not unless you have a process manager running which monitors it and the process monitor restarts it. Tornado in its single process mode will have the same problem. Using Tornado as the worker in Gunicorn is one way around that plus I believe Tornado itself may have some process manager in it now for running multiple process which allow it to restart processes if they die.
Do note that if your application bug which caused the Python exception is bad enough and it corrupts state within the process, subsequent requests may possibly have issues. This is the one difference with PHP. With PHP, after any request, whether successful or not, the application is effectively thrown away and doesn't persist. So buggy code cannot affect subsequent requests. In Python, because the process with loaded code and retained state is kept between requests, then technically you could get things in a state where you would have to restart the process to fix it. I don't know of any WSGI server though that has a mechanism to automatically restart a process if one request returned an error response.
If you're in an UNIX-like environment, you can run mod_wsgi under Apache in Daemon Mode. This means there will be a separate process for the Python code, and even if it crashes the server will continue running normally (and hopefully the WSGI process will restart itself). A WSGI application can run under multiple processes and multiple threads per process.
As for running multiple domains in the same server, check Name-Based Virtual Hosts.
Question pretty much says it all. If I am running Tornado on a server with Supervisor, what happens to active requests when I deploy code and need to restart the Tornado server? Are they dropped mid-request? Are they allowed to finish?
Supervisord send a signal like HUP or TERM to tornado process, the most important point is how tornado deal with it.
Unfortunately, tornado will simple exit when it get signal like HUP, TERM, INT.
Tornado has a sub module named autoreload, it make the application could detect the code files' changes and reload the application, but it only works the debug mode for one process, and not in WSGI applications. It's development tool.
But, we can define a function within run tornado.autoreload._reload function by manual, and register it for HUP sigal. tornado.autoreload.add_reload_hook can add functions should be called when reload.
Because the tornado doesn't manage the processes well on fork mode, so it's suggested running many independent processes for different ports. On this mode, the _reload will works like set debug flag.
After all, test and benchmark it for make sure it works well in your application.