Deploying a Simple WSGI Application on AWS¶
Let’s walk through manually deploying a simple WSGI application to an AWS EC2 instance we’ve created.
For this exercise we’ll use the fabfile you set up as part of the fabric walkthrough.
Setup¶
heffalump:~ cewing$ workon fabrictests
[fabrictests]
heffalump:fabrictests cewing$
In the fabric directory, create a very simple WSGI application. Start by
creating a new file myapp.py and opening it in your editor. In the file,
type the following Python code:
# -*- coding: utf-8 -*-
def app(environ, start_response):
data = "Hello, World!\n"
start_response("200 OK", [
("Content-Type", "text/plain"),
("Content-Length", str(len(data)))
])
return iter([data])
if __name__ == '__main__':
from wsgiref.simple_server import make_server
srv = make_server('localhost', 8080, app)
srv.serve_forever()
Test your application to be sure it works by running it from the command line:
source
Then, if you don’t already have one running, provision an AWS instance and
install nginx, using your fabfile:
[fabrictests]
heffalump:fabrictests cewing$ fab provision_instance
...
[fabrictests]
heffalump:fabrictests cewing$ fab install_nginx
[localhost] Executing task 'install_nginx'
Connected to EC2 region us-west-2
Please select from the following instances:
1: running instance i-08b12201
Choose an instance: 1
[ubuntu@ec2-54-184-162-20.us-west-2.compute.amazonaws.com] Executing task '_install_nginx'
...
Next, use the shell command scp to securely copy your wsgi application to
the new server instance:
[fabrictests]
heffalump:fabrictests cewing$ scp -i ~/.ssh/pk-cpe.pem myapp.py ubuntu@ec2-54-184-162-20.us-west-2.compute.amazonaws.com:~/
...
Are you sure you want to continue connecting (yes/no)? yes
...
myapp.py 100% 381 0.4KB/s 00:00
[fabrictests]
heffalump:fabrictests cewing$
Manual Configuration¶
We are going to do this manually once together. Afterwards, take what you
learned and automate these tasks using fabric.
Configure Nginx¶
The first step is to configure nginx to proxy HTTP requests to our simple
application.
If you know, or are more comfortable with the Apache webserver, you can
also use that. However, the trend I’ve seen over the last few years is toward
the use of nginx over the old stand-by.
Nginx stores site configuration on Ubuntu in the /etc/nginx/sites-available
directory.
Let’s shell into our new instance and look at what’s there:
[fabrictests]
heffalump:fabrictests cewing$ ssh -i ~/.ssh/pk-cpe.pem ubuntu@ec2-54-184-162-20.us-west-2.compute.amazonaws.com
Welcome to Ubuntu 12.04.4 LTS (GNU/Linux 3.2.0-58-virtual x86_64)
...
Last login: Wed Feb 26 19:10:01 2014 from 199.231.242.170
ubuntu@ip-10-254-159-140:~$ ls /etc/nginx/sites-available/
default
ubuntu@ip-10-254-159-140:~$ more /etc/nginx/sites-available/default
# You may add here your
# server {
# ...
# }
# statements for each of your virtual hosts to this file
...
ubuntu@ip-10-254-159-140:~$
The sites-available directory will hold individual site configuration for
all sites that might be available on a server.
Active site configuration is listed in the /etc/nginx/sites-enabled:
ubuntu@ip-10-254-159-140:~$ ls /etc/nginx/sites-enabled/
default
ubuntu@ip-10-254-159-140:~$ ls -l /etc/nginx/sites-enabled/
total 0
lrwxrwxrwx 1 root root 34 Feb 26 19:09 default -> /etc/nginx/sites-available/default
ubuntu@ip-10-254-159-140:~$
Notice that in fact, although default is in that directory too, it’s
actually a soft link to the file in sites-available.
Let’s move aside the existing default config and replace it with a simple
one of our own.
On your local machine, in the fabtests directory, make a new file
simple_nginx_config. Open that file in your editor and add the following:
server {
listen 80;
server_name http://ec2-54-184-162-20.us-west-2.compute.amazonaws.com/;
access_log /var/log/nginx/test.log;
location / {
proxy_pass http://127.0.0.1:8000;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}
}
Remember, you want to use the name of your actual server on aws, not the example used above.
Now, copy that file up to your server too:
[fabrictests]
heffalump:fabrictests cewing$ scp -i ~/.ssh/pk-cpe.pem simple_nginx_config ubuntu@ec2-54-184-162-20.us-west-2.compute.amazonaws.com:~/
simple_nginx_config 100% 363 0.4KB/s 00:00
[fabrictests]
heffalump:fabrictests cewing$
Next, on the server, move the original default configuration file aside and put your new one in its place:
ubuntu@ip-10-254-159-140:~$ ls
myapp.py simple_nginx_config
ubuntu@ip-10-254-159-140:~$ sudo mv /etc/nginx/sites-available/default /etc/nginx/sites-available/default.orig
ubuntu@ip-10-254-159-140:~$ sudo mv simple_nginx_config /etc/nginx/sites-available/default
ubuntu@ip-10-254-159-140:~$ ls -l /etc/nginx/sites-enabled/
total 0
lrwxrwxrwx 1 root root 34 Feb 26 19:09 default -> /etc/nginx/sites-available/default
ubuntu@ip-10-254-159-140:~$
Once that’s complete, you can restart nginx to have it pick up your changes:
ubuntu@ip-10-254-159-140:~$ sudo /etc/init.d/nginx restart
Restarting nginx: nginx: [warn] server name "http://ec2-54-184-162-20.us-west-2.compute.amazonaws.com/" has suspicious symbols in /etc/nginx/sites-enabled/default:3
nginx.
ubuntu@ip-10-254-159-140:~$
If you now try to load the public DNS name for your EC2 instance, you’ll see that nginx has updated and is now throwing an error:
http://ec2-54-184-162-20.us-west-2.compute.amazonaws.com
This should tell you Bad Gateway. That’s the error that means “I am a proxy, but the thing I’m proxying to is not running!”
Running a WSGI Server¶
Let’s make our wsgi app run, so we can fix that.
On your server, run the wsgi app:
ubuntu@ip-10-254-159-140:~$ python myapp.py
And now reload your web browser and verify that you can see “Hello, World!”
Automation¶
The steps we took there allowed us to upload an application and some
configuration to our server, apply the configuration to the nginx web
server we installed, and then run our WSGI application in a terminal to get a
response via public DNS.
Your next task is to automate this process using fabric.
For this task, You’ll want to look at two important sub-packages in fabric: