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 Boom to check if your proxy is behaving properly.

An example configuration file for fast clients with Nginx:

worker_processes 1;

user nobody nogroup;
# 'user nobody nobody;' for systems with 'nobody' as a group instead
pid /tmp/nginx.pid;
error_log /tmp/nginx.error.log;

events {
  worker_connections 1024; # increase if you have lots of clients
  accept_mutex off; # set to 'on' if nginx worker_processes > 1
  # 'use epoll;' to enable for Linux 2.6+
  # 'use kqueue;' to enable for FreeBSD, OSX
}

http {
  include mime.types;
  # fallback in case we can't determine a type
  default_type application/octet-stream;
  access_log /tmp/nginx.access.log combined;
  sendfile on;

  upstream app_server {
    # fail_timeout=0 means we always retry an upstream even if it failed
    # to return a good HTTP response

    # for UNIX domain socket setups
    server unix:/tmp/gunicorn.sock fail_timeout=0;

    # for a TCP configuration
    # server 192.168.0.7:8000 fail_timeout=0;
  }

  server {
    # if no Host match, close the connection to prevent host spoofing
    listen 80 default_server;
    return 444;
  }

  server {
    # use 'listen 80 deferred;' for Linux
    # use 'listen 80 accept_filter=httpready;' for FreeBSD
    listen 80;
    client_max_body_size 4G;

    # set the correct host(s) for your site
    server_name example.com www.example.com;

    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;
      # enable this if and only if you use HTTPS
      # proxy_set_header X-Forwarded-Proto https;
      proxy_set_header Host $http_host;
      # we don't want nginx trying to do something clever with
      # redirects, we set the Host: header above already.
      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_to_app {
    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.

Gunicorn 19 introduced a breaking change concerning how REMOTE_ADDR is handled. Previous to Gunicorn 19 this was set to the value of X-Forwarded-For if received from a trusted proxy. However, this was not in compliance with RFC 3875 which is why the REMOTE_ADDR is now the IP address of the proxy and not the actual user. You should instead configure Nginx to send the user’s IP address through the X-Forwarded-For header like this:

...
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
...

It is also worth noting that the REMOTE_ADDR will be completely empty if you bind Gunicorn to a UNIX socket and not a TCP host:port tuple.

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
$ pip install 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 gaffer

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 Gaffer.

Using a Procfile

Create a Procfile in your project:

gunicorn = gunicorn -w 3 test:app

You can launch 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
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. Below are configurations files and instructions for using systemd to create a unix socket for incoming Gunicorn requests. Systemd will listen on this socket and start gunicorn automatically in response to traffic. Later in this section are instructions for configuring Nginx to forward web traffic to the newly created unix socket:

/etc/systemd/system/gunicorn.service:

[Unit]
Description=gunicorn daemon
Requires=gunicorn.socket
After=network.target

[Service]
PIDFile=/run/gunicorn/pid
User=someuser
Group=someuser
RuntimeDirectory=gunicorn
WorkingDirectory=/home/someuser/applicationroot
ExecStart=/usr/bin/gunicorn --pid /run/gunicorn/pid   \
          --bind unix:/run/gunicorn/socket applicationname.wsgi
ExecReload=/bin/kill -s HUP $MAINPID
ExecStop=/bin/kill -s TERM $MAINPID
PrivateTmp=true

[Install]
WantedBy=multi-user.target

/etc/systemd/system/gunicorn.socket:

[Unit]
Description=gunicorn socket

[Socket]
ListenStream=/run/gunicorn/socket

[Install]
WantedBy=sockets.target

/etc/tmpfiles.d/gunicorn.conf:

d /run/gunicorn 0755 someuser somegroup -

Next enable the socket so it autostarts at boot:

systemctl enable gunicorn.socket

Either reboot, or start the services manually:

systemctl start gunicorn.socket

After running curl --unix-socket /run/gunicorn/socket http, Gunicorn should start and you should see some HTML from your server in the terminal.

You must now configure your web proxy to send traffic to the new Gunicorn socket. Configure your nginx.conf like the following:

/etc/nginx/nginx.conf::
http {

include mime.types; default_type application/octet-stream;

sendfile on; keepalive_timeout 65; disable_symlinks off;

server {
listen 8000; server_name 127.0.0.1;
location /static/ {
alias /static/;

}

location / {
proxy_set_header Host $http_host; proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_set_header X-Forwarded-Proto $scheme; proxy_pass http://unix:/run/gunicorn/socket;

}

}

Now make sure you enable the nginx service so it automatically starts at boot:

systemctl enable nginx.service

Either reboot, or start Nginx with the following command:

systemctl start nginx

Now you should be able to test Nginx with Gunicorn by visiting http://127.0.0.1:8000/ in any web browser. Please note that the listen and server_name used here are configured for a local machine. In a production server you will most likely listen on port 80, and use your URL as the server_name.

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)

Note

overriding the LOGGING dictionary requires to set disable_existing_loggers: False` to not interfere with the Gunicorn logging.

Warning

Gunicorn error log is here to log errors from Gunicorn, not from another application.