Deploying Gunicorn

We strongly recommend to use Gunicorn behind a proxy server.

Nginx Configuration

Although there are many HTTP proxies available, we strongly advise that you use Nginx. If you choose another proxy server you need to make sure that it buffers slow clients when you use default Gunicorn workers. Without this buffering Gunicorn will be easily susceptible to denial-of-service attacks. You can use slowloris to check if your proxy is behaving properly.

An example configuration file for fast clients with Nginx:

worker_processes 1;

user nobody nogroup;
pid /tmp/nginx.pid;
error_log /tmp/nginx.error.log;

events {
    worker_connections 1024;
    accept_mutex off;
}

http {
    include mime.types;
    default_type application/octet-stream;
    access_log /tmp/nginx.access.log combined;
    sendfile on;

    upstream app_server {
        server unix:/tmp/gunicorn.sock fail_timeout=0;
        # For a TCP configuration:
        # server 192.168.0.7:8000 fail_timeout=0;
    }

    server {
        listen 80 default;
        client_max_body_size 4G;
        server_name _;

        keepalive_timeout 5;

        # path for static files
        root /path/to/app/current/public;

        location / {
            # checks for static file, if not found proxy to app
            try_files $uri @proxy_to_app;
        }

        location @proxy_to_app {
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header Host $http_host;
            proxy_redirect off;

            proxy_pass   http://app_server;
        }

        error_page 500 502 503 504 /500.html;
        location = /500.html {
            root /path/to/app/current/public;
        }
    }
}

If you want to be able to handle streaming request/responses or other fancy features like Comet, Long polling, or Web sockets, you need to turn off the proxy buffering. When you do this you must run with one of the async worker classes.

To turn off buffering, you only need to add proxy_buffering off; to your location block:

...
location / {
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Host $http_host;
    proxy_redirect off;
    proxy_buffering off;

    proxy_pass http://app_server;
}
...

When Nginx is handling SSL it is helpful to pass the protocol information to Gunicorn. Many web frameworks use this information to generate URLs. Without this information, the application may mistakenly generate ‘http’ URLs in ‘https’ responses, leading to mixed content warnings or broken applications. In this case, configure Nginx to pass an appropriate header:

...
proxy_set_header X-Forwarded-Proto $scheme;
...

If you are running Nginx on a different host than Gunicorn you need to tell Gunicorn to trust the X-Forwarded-* headers sent by Nginx. By default, Gunicorn will only trust these headers if the connection comes from localhost. This is to prevent a malicious client from forging these headers:

gunicorn -w 3 --forwarded-allow-ips="10.170.3.217,10.170.3.220" test:app

When the Gunicorn host is completely firewalled from the external network such that all connections come from a trusted proxy (e.g. Heroku) this value can be set to ‘*’. Using this value is potentially dangerous if connections to Gunicorn may come from untrusted proxies or directly from clients since the application may be tricked into serving SSL-only content over an insecure connection.

Using Virtualenv

To serve an app from a Virtualenv it is generally easiest to just install Gunicorn directly into the Virtualenv. This will create a set of Gunicorn scripts for that Virtualenv which can be used to run applications normally.

If you have Virtualenv installed, you should be able to do something like this:

$ mkdir ~/venvs/
$ virtualenv ~/venvs/webapp
$ source ~/venvs/webapp/bin/activate
$ ~/venvs/webapp/bin/easy_install -U gunicorn
$ deactivate

Then you just need to use one of the three Gunicorn scripts that was installed into ~/venvs/webapp/bin.

Note: You can force the installation of Gunicorn in your Virtualenv by passing -I or --ignore-installed option to pip:

$ source ~/venvs/webapp/bin/activate
$ pip install -I gunicorn

Monitoring

Note

Make sure that when using either of these service monitors you do not enable the Gunicorn’s daemon mode. These monitors expect that the process they launch will be the process they need to monitor. Daemonizing will fork-exec which creates an unmonitored process and generally just confuses the monitor services.

Gaffer

Using Gafferd and gafferctl

Gaffer can be used to monitor gunicorn. A simple configuration is:

[process:gunicorn]
cmd = gunicorn -w 3 test:app
cwd = /path/to/project

Then you can easily manage Gunicorn using gafferctl.

Using a Procfile

Create a Procfile in your project:

gunicorn = gunicorn -w 3 test:app

You can any other applications that should be launched at the same time.

Then you can start your gunicorn application using gaffer.:

gaffer start

If gafferd is launched you can also load your Procfile in it directly:

gaffer load

All your applications will be then supervised by gafferd.

Runit

A popular method for deploying Gunicorn is to have it monitored by runit. Here is an example service definition:

#!/bin/sh

GUNICORN=/usr/local/bin/gunicorn
ROOT=/path/to/project
PID=/var/run/gunicorn.pid

APP=main:application

if [ -f $PID ]; then rm $PID; fi

cd $ROOT
exec $GUNICORN -c $ROOT/gunicorn.conf.py --pid=$PID $APP

Save this as /etc/sv/[app_name]/run, and make it executable (chmod u+x /etc/sv/[app_name]/run). Then run ln -s /etc/sv/[app_name] /etc/service/[app_name]. If runit is installed, gunicorn should start running automatically as soon as you create the symlink.

If it doesn’t start automatically, run the script directly to troubleshoot.

Supervisor

Another useful tool to monitor and control Gunicorn is Supervisor. A simple configuration is:

[program:gunicorn]
command=/path/to/gunicorn main:application -c /path/to/gunicorn.conf.py
directory=/path/to/project
user=nobody
autostart=true
autorestart=true
redirect_stderr=true

Upstart

Using gunicorn with upstart is simple. In this example we will run the app “myapp” from a virtualenv. All errors will go to /var/log/upstart/myapp.log.

/etc/init/myapp.conf:

description "myapp"

start on (filesystem)
stop on runlevel [016]

respawn
console log
setuid nobody
setgid nogroup
chdir /path/to/app/directory

exec /path/to/virtualenv/bin/gunicorn myapp:app

Systemd

A tool that is starting to be common on linux systems is Systemd. Here are configurations files to set the gunicorn launch in systemd and the interfaces on which gunicorn will listen. The sockets will be managed by systemd:

gunicorn.service:

[Unit]
Description=gunicorn daemon

[Service]
Type=forking
PIDFile=/home/urban/gunicorn/gunicorn.pid
User=someuser
WorkingDirectory=/home/urban/gunicorn/bin
ExecStart=/home/someuser/gunicorn/bin/gunicorn -p /home/urban/gunicorn/gunicorn.pid- test:app
ExecReload=/bin/kill -s HUP $MAINPID
ExecStop=/bin/kill -s QUIT $MAINPID
PrivateTmp=true

gunicorn.socket:

[Unit]
Description=gunicorn socket

[Socket]
ListenStream=/run/gunicorn.sock
ListenStream=0.0.0.0:9000
ListenStream=[::]:8000

[Install]
WantedBy=sockets.target

After running curl http://localhost:9000/ gunicorn should start and you should see something like that in logs:

2013-02-19 23:48:19 [31436] [DEBUG] Socket activation sockets: unix:/run/gunicorn.sock,http://0.0.0.0:9000,http://[::]:8000

Logging

Logging can be configured by using various flags detailed in the configuration documentation or by creating a logging configuration file. Send the USR1 signal to rotate logs if you are using the logrotate utility:

kill -USR1 $(cat /var/run/gunicorn.pid)