Flask Traditional Deployments: Zero to One <Deploy uWSGI>

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The following article will introduce how to install a production-ready web server.

Background

  • A quite developed web project ( For Flask case, flask run listens 127.0.0.1:5000 by default. However, flask run --host 0.0.0.0 listens a.b.c.d:5000 under the same wifi. Have fun with it first, then come and playing with VPS! )
  • This series is a supplyment for Tradition Deploments in Chapter 17. Deployment in Flask Web Development, 2nd Edition written by Miguel Grinberg.

0. Try uWSGI

Official documents: https://uwsgi-docs.readthedocs.io/en/latest/WSGIquickstart.html

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$ uwsgi --http 127.0.0.1:3031 --wsgi-file v1siuol.py --callable app --processes 4 --threads 2 --stats 127.0.0.1:9191

We choose --http instead of --socket since we will use uwsgitop later to determine how many processes and thread are optimal.

There is no magic rule for setting the number of processes or threads to use. It is very much application and system dependent. Simple math like processes = 2 * cpucores will not be enough. You need to experiment with various setups and be prepared to constantly monitor your apps. uwsgitop could be a great tool to find the best values.

Reference: https://uwsgi-docs.readthedocs.io/en/latest/ThingsToKnow.html

Running the above line, we are expecting to see something like:

1. Config uWSGI

Keep uWSGI running, we now open another terminal, logging in the server via ssh.

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# After login, new ssh connection
$ cd flask/
$ cd v1siuol-site/
$ source venv/bin/activate
(venv)$ uwsgitop :9191

The port uwsgitop listen to should be the same as the port uWSGI put the stat in.

Since uwsgi and uwsgitop are ocupying two terminals, we open the third terminal to simulate the regular access to our flask website.

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# After login, another new ssh connection
$ curl -v localhost:3031  # You may repeat it, but this only accesses index page

Meanwhile, CHECK your uwsgitop window.

See! Here we moniter the reaction under 4 processes, each with 2 threads. Obviously, we don’t need that much (though we only consider one connection cases).

Try a few times and find the best values. THEN we shall move to the next step, configing uWSGI in a more proper way.

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(venv)$ sudo mkdir /etc/uwsgi
(venv)$ sudo chmod 777 /etc/uwsgi 
(venv)$ touch /etc/uwsgi/emperor.ini
(venv)$ vim /etc/uwsgi/emperor.ini

> [ emperor.ini ]

In emperor.ini :

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[uwsgi]
emperor = /etc/uwsgi/vassals
uid = 1000
gid = 1000
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(venv)$ sudo touch /etc/systemd/system/uwsgi_v1siuol.service 
(venv)$ chmod 777  /etc/systemd/system/uwsgi_v1siuol.service
(venv)$ vim /etc/systemd/system/uwsgi_v1siuol.service

> [ uwsgi_v1siuol.service ]

In uwsgi_v1siuol.service :

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[Unit]
Description=uWSGI instance to serve flask
After=syslog.target

[Service]
ExecStart=/home/ubuntu/flask/v1siuol-site/venv/bin/uwsgi --ini /etc/uwsgi/emperor.ini
# Requires systemd version 211 or newer
RuntimeDirectory=uwsgi
Restart=always
KillSignal=SIGQUIT
Type=notify
NotifyAccess=all

[Install]
WantedBy=multi-user.target
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(venv)$ sudo systemctl start uwsgi_v1siuol.service
(venv)$ systemctl status uwsgi_v1siuol.service  # check if active

We are almost there, but one vassal left.

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(venv)$ sudo systemctl stop uwsgi_v1siuol.service
(venv)$ touch /etc/uwsgi/vassals/uwsgiconfig.ini

> [ uwsgiconfig.ini ]

In uwsgiconfig.ini :

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[uwsgi]

chdir = /home/ubuntu/flask/v1siuol-site

socket = /home/ubuntu/flask/v1siuol-site/logs/uwsgi.sock
chmod-socket = 666
stats = /home/ubuntu/flask/v1siuol-site/logs/uwsgi_stat.sock

wsgi-file = v1siuol.py
callable = app

logto = /home/ubuntu/flask/v1siuol-site/logs/uwsgi.log

Try again!

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(venv)$ sudo systemctl start uwsgi_v1siuol.service
(venv)$ ps aux | grep uwsgi

ubuntu 23216 0.0 0.4 34696 4252 ? Ss 13:53 0:00 /home/ubuntu/flask/v1siuol-site/venv/bin/uwsgi --ini /etc/uwsgi/emperor.ini
ubuntu 23218 0.4 6.1 144172 62620 ? S 13:53 0:00 /home/ubuntu/flask/v1siuol-site/venv/bin/uwsgi --ini uwsgiconfig.ini
ubuntu 23222 0.0 5.3 144172 54456 ? S 13:53 0:00 /home/ubuntu/flask/v1siuol-site/venv/bin/uwsgi --ini uwsgiconfig.ini
ubuntu 23236 0.0 0.1 12916 1084 pts/1 S+ 13:55 0:00 grep --color=auto uwsgi

Great! We finally daemonize uWSGI. BUT plz never ever daemonize the Emperor unless you know what you are doing!!!

2. Kill uWSGI

Now you can do something really fun.

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(venv)$ ps aux | grep uwsgi

ubuntu 23216 0.0 0.4 34696 4252 ? Ss 13:53 0:00 /home/ubuntu/flask/v1siuol-site/venv/bin/uwsgi --ini /etc/uwsgi/emperor.ini
ubuntu 23218 0.0 6.1 144172 62620 ? S 13:53 0:00 /home/ubuntu/flask/v1siuol-site/venv/bin/uwsgi --ini uwsgiconfig.ini
ubuntu 23222 0.0 5.3 144172 54456 ? S 13:53 0:00 /home/ubuntu/flask/v1siuol-site/venv/bin/uwsgi --ini uwsgiconfig.ini
ubuntu 23368 0.0 0.0 12916 932 pts/1 S+ 15:31 0:00 grep --color=auto uwsgi

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(venv)$ kill -INT 23222
(venv)$ ps aux | grep uwsgi

ubuntu 23216 0.0 0.4 34696 4252 ? Ss 13:53 0:00 /home/ubuntu/flask/v1siuol-site/venv/bin/uwsgi --ini /etc/uwsgi/emperor.ini
ubuntu 23218 0.0 6.1 144172 62620 ? S 13:53 0:00 /home/ubuntu/flask/v1siuol-site/venv/bin/uwsgi --ini uwsgiconfig.ini
ubuntu 23382 0.0 5.3 144172 54456 ? S 15:40 0:00 /home/ubuntu/flask/v1siuol-site/venv/bin/uwsgi --ini uwsgiconfig.ini
ubuntu 23384 0.0 0.1 12916 1016 pts/1 S+ 15:40 0:00 grep --color=auto uwsgi

Can you tell the difference of the starting time and pid between processes?

pid: 23382 is reloaded!!!

Try to kill another one.

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(venv)$ kill -INT 23218
(venv)$ ps aux | grep uwsgi

ubuntu 23216 0.0 0.4 34664 4264 ? Ss 13:53 0:00 /home/ubuntu/flask/v1siuol-site/venv/bin/uwsgi --ini /etc/uwsgi/emperor.ini
ubuntu 23389 65.0 6.1 144188 62760 ? S 15:40 0:00 /home/ubuntu/flask/v1siuol-site/venv/bin/uwsgi --ini uwsgiconfig.ini
ubuntu 23392 0.0 5.3 144188 54372 ? S 15:40 0:00 /home/ubuntu/flask/v1siuol-site/venv/bin/uwsgi --ini uwsgiconfig.ini
ubuntu 23394 0.0 0.1 12916 1088 pts/1 S+ 15:40 0:00 grep --color=auto uwsgi

Surprise! They all being reloaded!

3. Conclusion

For editing files reference:

/etc/uwsgi/emperor.ini

/etc/uwsgi/vassals/uwsgiconfig.ini

/etc/systemd/system/uwsgi_v1siuol.service

For log files reference:

/home/ubuntu/flask/v1siuol-site/logs/uwsgi.log

/home/ubuntu/flask/v1siuol-site/logs/uwsgi.sock

/home/ubuntu/flask/v1siuol-site/logs/uwsgi_stat.sock

Thank you.

References:

  • https://uwsgi-docs.readthedocs.io/en/latest/Systemd.html
  • https://uwsgi-docs.readthedocs.io/en/latest/Emperor.html
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