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phusion / passenger-python-flask-demo

Passenger: Flask example app
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Issue in NginX/Passenger/Flask app/Ubuntu 16.04 online Tutorial: setup not working #1

Open tony-bony opened 4 years ago

tony-bony commented 4 years ago

Issue report

Question 1: What is the problem?: I want to install Nginx and Passenger on Ubuntu 16.04 to run python apps e.g. using Flask and I run into issues. When I visit my server http://hXXXXXXX.stratoserver.net/ in the browser I am getting:

We're sorry, but something went wrong.

Question 2: Passenger version and integration mode: Passenger open source 6.0.4 + Nginx

Question 3: OS or Linux distro, platform (including version): Ubuntu 16.04 LTS 

$ uname -a
Linux hXXXXXXX.stratoserver.net 4.4.0-042stab141.3 phusion/passenger#1 SMP Fri Nov 15 22:45:34 MSK 2019 x86_64 x86_64 x86_64 GNU/Linux
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 16.04.6 LTS
Release:    16.04
Codename:   xenial

Question 4: Passenger installation method: Nginx + Phusion APT repo

Question 5: Your app's programming language (including any version managers) and framework (including versions): Python 3.7.6 + Flask 1.1.1

Question 6: Are you using a PaaS and/or containerization? If so which one? NA

Question 7: Anything else about your setup that we should know? I have a VPS at strato.nl with Ubuntu 16.04 installed, and the host address is: http://hXXXXXXX.stratoserver.net/ and I was following "Deploying a Python app with Passenger to production" tutorial with the following infrastructure:

Linux/Unix
Nginx
Passenger open source
Python installed via LinuxBrew
Passenger installed on Ubuntu 16.04 LTS
Demo Flask app from github

So the demo Flask app was cloned like this: git clone https://github.com/phusion/passenger-python-flask-demo.git

Running passenger-memory-stats gives:

$ sudo /usr/sbin/passenger-memory-stats
Version: 6.0.4
Date   : 2020-01-29 13:12:15 +0100
------------- Apache processes -------------
*** WARNING: The Apache executable cannot be found.
Please set the APXS2 environment variable to your 'apxs2' executable's filename, or set the HTTPD environment variable to your 'httpd' or 'apache2' executable's filename.

---------- Nginx processes -----------
PID    PPID   VMSize    Private  Name
--------------------------------------
23320  1      174.9 MB  0.8 MB   nginx: master process /usr/sbin/nginx -g daemon on; master_process on;
23325  23320  174.9 MB  0.8 MB   nginx: worker process
### Processes: 2
### Total private dirty RSS: 1.54 MB

----- Passenger processes -----
PID    VMSize    Private  Name
-------------------------------
23309  445.7 MB  2.5 MB   Passenger watchdog
23312  672.3 MB  7.5 MB   Passenger core
### Processes: 2
### Total private dirty RSS: 9.98 MB

When I run the app locally on the server everything works as expected:

$ python app.py
 * Serving Flask app "app" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

Then in another terminal:

$ curl localhost:5000
<!DOCTYPE html>
<html>
<head>
  <title>Hello</title>
  <style>
    html, body {
      font-family: sans-serif;
      background: #f0f0f0;
      margin: 4em;
    }

    .main {
      background: white;
      border: solid 1px #c0c0c0;
      border-radius: 8px;
      padding: 2em;
    }
  </style>
</head>
<body>

  <section class="main">
    <h1>Hello world!</h1>
    <p>Welcome to the Passenger Flask example app.</p>
  </section>

</body>
</html>

So it looks like locally all works fine. However when I visit http://hXXXXXXX.stratoserver.net/ in the browser I got an error page like described above.

The nginx error /var/log/nginx/error.log:


App 29730 output: Traceback (most recent call last):
App 29730 output:   File "/usr/share/passenger/helper-scripts/wsgi-loader.py", line 369, in <module>
App 29730 output:
App 29730 output: app_module = load_app()
App 29730 output:   File "/usr/share/passenger/helper-scripts/wsgi-loader.py", line 76, in load_app
App 29730 output:
App 29730 output: return imp.load_source('passenger_wsgi', startup_file)
App 29730 output:   File "/var/www/demoapp/code/passenger_wsgi.py", line 3, in <module>
App 29730 output:
App 29730 output: from app import MyApp as application
App 29730 output:   File "/var/www/demoapp/code/app.py", line 1, in <module>
App 29730 output:
App 29730 output: from flask import Flask, render_template
App 29730 output: ImportError
App 29730 output: :
App 29730 output: No module named flask

It seems the server uses Python2 by default. I need it to use Python3 where I installed Flask. How can I setup the Python version and Python libraries in Nginx/Passenger?

My demoapp.conf is:

$ vi /etc/nginx/sites-enabled/demoapp.conf
server {
    listen 80;
    server_name hXXXXXXX.stratoserver.net;

    # Tell Nginx and Passenger where your app's 'public' directory is
    root /var/www/demoapp/code/public;

    # Turn on Passenger
    passenger_enabled on;
    passenger_app_env development;
    passenger_friendly_error_pages off;
    passenger_user demoapp;

}

What are the passenger / Nginx settings that I need to set to successfully run a Flask application? How can I set Passenger/Nginx to use Python3 and Python3 libraries?

tony-bony commented 4 years ago

The solution for me was to add passenger_python /home/linuxbrew/.linuxbrew/bin/python3; to the demoapp.conf. So it should look like:

server {
    listen 80;
    server_name hXXXXXXX.stratoserver.net;

    # Tell Nginx and Passenger where your app's 'public' directory is
    root /var/www/demoapp/code/public;
    passenger_python /home/linuxbrew/.linuxbrew/bin/python3;

    # Turn on Passenger
    passenger_enabled on;
    passenger_user demoapp;
}

This way Passenger is using Python3 and this is where I installed Flask. Maybe you could adit your tutorial to include this information?

Also the Passenger installation for Nginx should not include Apache support.

pauljohn32 commented 4 years ago

You should use a python virtual environment and, as you note, the path tug o the python executable can be supplied. However, your comment confuses the issue somewhat. Flask is not a production level tool and you need Passenger and the wsgi application server to replace flask.

tony-bony commented 4 years ago

Yes, using the virtual environment was the next step but online tutorial does not specify it is required for the Flask demo app as far as I recall. I know Flask is an application framework and I am running a Flask app on Nginx/Phusion Passenger server.