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Deploying Flask (WSGI)
Applications
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Matt Wright @mattupstate
Engineer @ChatID
● Python, Ruby, CoffeeScript
● Flask, Chef, AngularJS
Open Source
● Flask-Security
● Flask-Social
● Flask-Mail + a few others
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WSGI
(Web Server Gateway Interface)
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PEP 333
http://legacy.python.org/dev/peps/pep-0333/
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# ~/hello.py
def application(environ, start_response):
start_response('200 OK',
[('Content-Type','text/html')])
return ["Hello World"]
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# ~/app.py
from flask import Flask
app = Flask(__name__)
@app.route('/')
@app.route('/')
def catch_all(path=''):
return 'Hello World'
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Browser
WSGI
Gateway
WSGI
App
1 2
4 3
Request Flow
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Browser
WSGI
Gateway
WSGI
App
1
1. Browser sends an HTTP request
to the gateway server
Request Flow
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Browser
WSGI
Gateway
WSGI
App
2
2. Gateway server prepares and sends the
request to the WSGI compatible application
1
Request Flow
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Browser
WSGI
Gateway
WSGI
App
1 2
3
3. Application processes the request
and returns a response
Request Flow
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Browser
WSGI
Gateway
WSGI
App
1 2
4 3
4. The gateway server returns the
response to the browser
Request Flow
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Browser
WSGI
Gateway
WSGI
Middle-
ware
WSGI
App
Middleware
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Browser
WSGI
Gateway
WSGI
Middle-
ware
WSGI
App
WSGI
Middle-
ware
WSGI
Middle-
ware
WSGI
Middle-
ware
WSGI
Middle-
ware
MOAR MIDDLEWARE!
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Gateway Servers
(sometimes called “containers”)
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http://www.tornadoweb.org/
Tornado
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1. Written in Python!
2. Web application framework
3. Asynchronous networking library
4. WSGI support
Tornado
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# ~/tor.py
from tornado.wsgi import WSGIContainer
from tornado.httpserver import HTTPServer
from tornado.ioloop import IOLoop
from app import app
http_server = HTTPServer(WSGIContainer(app))
http_server.listen(8000)
IOLoop.instance().start()
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matt @ pc in ~/
$ mkvirtualenv wsgi
matt @ pc in ~/ workon:wsgi
$ pip install flask tornado
matt @ pc in ~/ workon:wsgi
$ python tor.py
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matt @ pc in ~/
$ curl localhost:8000
Hello World
matt @ pc in ~/ workon:wsgi
$ pip install tornado
matt @ pc in ~/ workon:wsgi
$ python tor.py
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http://www.gevent.org/
gevent
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1. Written in Python!
2. Coroutine networking library
3. 3rd party module support
gevent
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# ~/ge.py
from gevent.wsgi import WSGIServer
from app import app
server = WSGIServer(('', 8000), app)
server.serve_forever()
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matt @ pc in ~/ workon:wsgi
$ pip install gevent
matt @ pc in ~/ workon:wsgi
$ python ge.py
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matt @ pc in ~/
$ curl localhost:8000
Hello World
matt @ pc in ~/ workon:wsgi
$ pip install gevent
matt @ pc in ~/ workon:wsgi
$ python ge.py
127.0.0.1 - - [2014-06-24...
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http://gunicorn.org/
Gunicorn
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Gunicorn
1. Written in Python!
2. Easy configuration
3. Broadly compatible
4. Extensible
5. Fairly speedy
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matt @ pc in ~/ workon:wsgi
$ pip install gunicorn
matt @ pc in ~/ workon:wsgi
$ gunicorn app:app
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matt @ pc in ~/
$ curl localhost:8000
Hello World
matt @ pc in ~/
$ mkvirtualenv wsgi
matt @ pc in ~/ workon:wsgi
$ pip install gunicorn flask
matt @ pc in ~/ workon:wsgi
$ gunicorn app:app
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https://uwsgi-docs.readthedocs.org/
uWSGI
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uWSGI
1. Support for many platforms and languages
2. Multiple configuration formats
3. Flexible logging
4. Extensible
5. Speaks HTTP and uwsgi
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matt @ pc in ~/ workon:wsgi
$ pip install uwsgi
matt @ pc in ~/ workon:wsgi
$ uwsgi --http :8000 -w app:app
...
spawned uWSGI worker 1 ...
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matt @ pc in ~/
$ curl localhost:8000
Hello World
matt @ pc in ~/ workon:wsgi
$ pip install uwsgi
matt @ pc in ~/ workon:wsgi
$ uwsgi --http :8000 -w app:app
...
spawned uWSGI worker 1 ...
[pid: 42176|app: 0|req: ...
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(how to start your app)
Process Management
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http://upstart.ubuntu.com/
upstart
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# /etc/init/hello-world.conf
description "Hello World app"
start on runlevel [2345]
stop on runlevel [06]
chdir /srv/hello-world
exec /usr/local/bin/uwsgi \
--die-on-term \
--http :8000 \
-w app:app
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http://www.freedesktop.org/wiki/Software/systemd/
systemd
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# /etc/systemd/system/hello-world.service
[Unit]
Description=Hello World app
[Service]
ExecStart=/usr/local/bin/uwsgi \
--die-on-term \
--http :8000 \
-w app:app
[Install]
WantedBy=multi-user.target
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http://supervisord.org/
supervisord
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# /etc/supervisor.d/hello-world.conf
[program:hello-world]
directory=/srv/hello-world
command=/usr/local/bin/uwsgi \
--die-on-term \
--http :8000 \
-w app:app
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(some things are better than others)
Reverse Proxies
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Why?
● Static files
● URL rewrites
● Routing
● Header mods
● App aggregation
● and many more!
● Network security
● Authentication
● Load balancing
● SSL termination
● Compression
● Caching
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http://www.nginx.org/
Apache
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# /etc/apache2/sites-enabled/hello-world.conf
ServerName hello-world.com
ProxyPreserveHost On
ProxyPass /static !
Alias /static "/srv/hello-world/static"
ProxyPass / http://127.0.0.1:8000/
ProxyPassReverse / http://127.0.0.1:8000/
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http://www.nginx.org/
Nginx
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# /etc/nginx/sites-enabled/hello-world.conf
server {
listen 80;
server_name hello-world.com;
location / {
proxy_pass http://127.0.0.1:8000;
}
location ^~ /static/ {
root /srv/hello-world/static;
}
}
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(is hard)
Concurrency
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Concurrency Models
callback/generator (auto)
lightweight threads (auto)
processor/thread (config)
processor/thread (config)
Tornado
gevent
Gunicorn
uWSGI
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Increasing Concurrency
processes
processes
workers + processes
workers + processes
Tornado
gevent
Gunicorn
uWSGI
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Increasing Workers
Gunicorn
uWSGI
--workers
--workers
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DISCLAIMER!
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(when one server isn’t enough)
Load Balancing
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Machine Level
App Server
192.168.1.101
App Server
192.168.1.102
App Server
192.168.1.102
Primary
Load Balancer
192.168.1.100
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# /etc/nginx/sites-enabled/load-balancer.conf
upstream app_upstream {
least_conn;
server 192.168.1.101:8000
server 192.168.1.102:8000
server 192.168.1.103:8000
}
server {
listen 80;
server_name hello-world.com;
location / {
proxy_pass http://app_upstream;
}
}
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Machine + Process Level
App Server
192.168.1.101
App Server
192.168.1.102
App Server
192.168.1.102
Primary
Load Balancer
192.168.1.100
t
127.0.0.1:8001
127.0.0.1:8002
127.0.0.1:8000 127.0.0.1:8000
127.0.0.1:8001
127.0.0.1:8002
127.0.0.1:8000
127.0.0.1:8001
127.0.0.1:8002
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# /etc/supervisor.d/hello-world.conf
[program:hello-world]
numprocs=3
process_name=hello-world%(process_num)
directory=/srv/hello-world
command=/usr/local/bin/uwsgi \
--die-on-term \
--http :80%(process_num)02d \
-w app:app
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# /etc/nginx/sites-enabled/hello-world.conf
upstream local_upstream {
least_conn;
server 127.0.0.1:8000
server 127.0.0.1:8001
server 127.0.0.1:8002
}
server {
listen 80;
server_name hello-world.com;
location / {
proxy_pass http://local_upstream;
}
}
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(I’ve failed at this a lot)
Recommendations
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1. Use virtualenv and pip
2. Don’t use virtualenvwrapper
3. Use a `requirements.txt` file
Python
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1. Provide default settings
2. Enable settings to be overridden
a. Environment Variable(s)
b. Default file locations
3. Raise an error at startup when required
settings are missing
4. Generate a `SECRET_KEY` with `os.
urandom(16)`
Configuration
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1. Prefer the uwsgi protocol over HTTP
2. Prefer TCP sockets over Unix sockets
3. Lots of useful options
a. virtualenv + pythonpath
b. enable-threads + lazy-apps
c. need-app
d. stats
Use uWSGI
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1. Pass custom headers
2. Lots of useful modules
a. ngx_http_geoip_module
b. ngx_http_gzip_module
c. ngx_http_memcached_module
d. ngx_http_status_module
Use Nginx
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(putting it all together)
Automation
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http://www.ansible.com/
Ansible
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(because what could go wrong?)
Demo
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Thank You!
mattupstate.com
gittip.com/mattupstate
github.com/mattupstate
twitter.com/mattupstate