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How to proxy web apps using nginx?

Virtual Hosts on nginx (CSC309)

When hosting our web applications, we often have one public IP address (i.e., an IP address visible to the outside world) using which we want to host multiple web apps. For example, one may wants to host three different web apps respectively for example1.com, example2.com, and example1.com/images on the same machine using a single IP address.

How can we do that? Well, the good news is Internet browsers send the domain name inside HTTP requests and all we need to do is to parse the requested domain name and URL and then route the HTTP request to the actual web server.

Oh, do I really need to parse HTTP requests? You can if you really want to, but there are lots of tools and technologies that readily do this for you. In this tutorial, we walk you through how you can use nginx to proxy multiple web applications.

Install nginx

CDF @UofT

We have prepared pre-copmiled binaries for your. You need to download nginx.tar.gz and uncompress it:

$ wget http://www.cs.toronto.edu/~soheil/csc309/nginx.tar.gz && tar -xvzf nginx.tar.gz
  • It creates an nginx directory for you. The config file is in nginx/conf/nginx.conf.
  • We have provided a script named nginx in the directory. To run nginx, go to the nginx directory (cd nginx) and run ./nginx ....

Ubuntu

Install nginx using apt-get:

$ sudo apt-get install nginx

Notes:

  • The part of the nginx's config file we need resides in /etc/nginx/sites-enabled/default.
  • To edit the config file or run nginx, you need to use sudo.

Mac OS

Install homebrew, and then install nginx using brew:

$ brew install nginx

Notes:

  • nginx's config file is in /usr/local/etc/nginx/nginx.conf.
  • To edit the config file or run nginx, you need to use sudo: sudo nano /usr/local/etc/nginx/nginx.conf and sudo nginx ...

Configuration

Step 1 -- Booting Servers for Virtual Hosts

Write three different node applications running on different ports (say 8080, 8181, 8282) on your machine.

Step 2 -- Configure nginx's Port

To do so, you need to edit your nginx config file.

In the config file, find the server section:

server {
    listen       80;
    ...
    location / {
       ...
    }
    ...
}

If you're using CDF, make sure you change 80 to a vacant port number (ask for one from your instructor). If not, you can keep using 80 or change the port if you will.

Test nginx

  1. Run ./nginx on CDF, or run sudo nginx on your local machine.
  2. Open the browser and log on to localhost:$PORT (replace $PORT with the port number you configured for nginx).

Step 3 -- Configure /

Let say we want to configure nginx to route requests for /, /blog, and /mail, respectively onto localhost:8080, localhost:8181, and localhost:8282.

                  +--- host --------> node.js on localhost:8080
                  |
users --> nginx --|--- host/blog ---> node.js on localhost:8181
                  |
                  +--- host/mail ---> node.js on localhost:8282

To route /, you need to edit your nginx config file.

In the config file, find the server section:

server {
    listen       80;
    ...
    location / {
       ...
    }
    ...
}

This section is simply telling nginx how it should serve HTTP requests.

Now, change the location section to this snippet:

server {
    listen       ...;
    ...
    location / {
        proxy_pass http://127.0.0.1:8080;
    }
    ...
}

proxy_pass simply tells nginx to forward requests to / to the server listening on http://127.0.0.1:8080.

Step 4 -- Reload nginx's Configuration

To reload nginx's configuration run: nginx -s reload on your machine.

Referesh your browser. Do you see the output from your node.js application? If yes, you are all set. If no, there is a problem with your config.

Step 5 -- Add /blog and /mail

To redirect /mail and /blog, you simply need to add new entries the location section in the config file:

server {
    listen       ...;
    ...
    location / {
        proxy_pass http://127.0.0.1:8080;
    }
    
    location /blog {
        proxy_pass http://127.0.0.1:8181;
    }

    location /mail {
        proxy_pass http://127.0.0.1:8282;
    }
    ...
}

Step 6 -- Reload Your nginx Configuration

Run nginx -s reload on your machine.

Log onto localhost:$PORT/blog in your browser. Do you see the output from your second node.js application?

Then log onto localhost:$PORT/mail. Do you see the output from your third node.js application?

If yes & yes, you are all set. If no, there is a problem with your config.

Step 7 -- Rewriting Requests

Now as you might have noticed in Step 6, nginx sends the same HTTP request to your node.js web apps which results into a 404 error. Why? Because, your node.js web application serves requests from / not from /blog and /mail. But, nginx is sending requests to /blog and /mail.

To fix this issue, we need rewrite the URL so that it matches the URL you can serve on your node.js applications.

To correctly rewrite URLs change your config file to match the following snippet:

server {
    listen       ...;
    ...
    location / {
        proxy_pass http://127.0.0.1:8080;
    }
    
    location /blog {
        rewrite ^/blog(.*) /$1 break;
        proxy_pass http://127.0.0.1:8181;
    }

    location /mail {
        rewrite ^/mail(.*) /$1 break;
        proxy_pass http://127.0.0.1:8282;
    }
    ...
}

This rewrite commands are simple regular expressions that transform strings like /blogWHAT_EVER and /mailWHAT_EVER to /WHAT_EVER in the HTTP requests.

Step 8 -- Reload and Test.

All set?

Exercise 1

Configure your nginx to redirect URLs from /google to http://www.google.com

Step 9 (optional) -- Redirecting Based on Host Name

Let say you want to host example1.com, example2.com, and example3.com on your machine, respectively to localhost:8080, localhost:8181, and localhost:8282.

Note: Since you don't have access to a DNS server, you should add domain name entries to your /etc/hosts (you can't do this on CDF machines):

...
127.0.0.1 example1.com example2.com example3.com
...

To proxy eaxmple1.com we can't use the location part of the default server. Instead we need to add another server section with a server_name set to our virtual host (e.g., example1.com, ...), and then a simple location section that tells nginx how to proxy the requests:

server {
    listen       80;
    server_name  example1.com;

    location / {
        proxy_pass http://127.0.0.1:8080;
    }
}

server {
    listen       80;
    server_name  example2.com;

    location / {
        proxy_pass http://127.0.0.1:8181;
    }
}

server {
    listen       80;
    server_name  example3.com;

    location / {
        proxy_pass http://127.0.0.1:8282;
    }
}

Simple, ha?!

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