HOW TO : Configure nginx to use URI for modifying response content

That was a pretty long title for the post :). I love nginx for it’s flexibility and ease of use. It is like a swiss army knife.. can do a lot of things :).

We needed to serve some dynamic content for one of our use cases. If user visits a site using the following URL format http://example.com/23456789/678543 , we want to respond with some html content that is customized using the 23456789 and 678543 strings.

A picture might help here

Here’s how this was achieved

  • Define a location section in the nginx config to respond to the URL path specified and direct it to substitute content
    location ~ "^/(?<param1>[0-9]{8})/(?<param2>[0-9]{6})" {

            root /var/www/html/test/;
            index template.html;
            sub_filter_once off;
            sub_filter '_first_param_' '$param1';
            sub_filter '_second_param_' '$param2';
            rewrite ^.*$ /template.html break;
    }

create a file named template.html with the following content in /var/www/html/test

Breaking down the config one line at a time

location ~ "^/(?<param1>[0-9]{8})/(?<param2>[0-9]{6})" : The regex is essentially matching for the first set of digits after the / and adding that as the value for variable $param1. The first match is a series of 8 digits with each digit in the range 0-9. The second match is for a series of 6 digits with each digit in the range 0-9 and it will be added as the value for variable $param2

root /var/www/html/test/; : Specifying the root location for the location.

index template.html; : Specifying the home page for the location.

sub_filter_once off; : Specify to the sub_filter module to not stop after the first match for replacing response content. By default it processes the first match and stops.

sub_filter 'first_param' '$param1'; : Direct the sub_filter module to replace any text matching first_param in the response html with value in variable $param1.

sub_filter 'second_param' '$param2'; : Direct the sub_filter module to replace any text matching second_param in the response html with value in variable $param1.

rewrite ^.*$ /template.html break; : Specify nginx to server template.html regardless of the URI specified.

Big thanks to Igor for help with the configs!!

HOW TO : Configure nginx for WordPress permalinks

Over the last week, I moved this blog from a LAMP (Linux, Apache, MySQL, PHP) stack to LEMP (Linux, Nginx, MySQL, PHP) stack. Have a blog post in the works with all the gory details, but wanted to quick document a quirk in the WordPress + Nginx combination that broke permalinks on this site.

Permalinks are user friendly permanent static URLs for a blog post. So for example this particular blog post’ URL is

https://kudithipudi.org/2017/02/24/how-to-configure…press-permalinks/

instead of

https://kudithipudi.org/?p=1762

This works by default in Apache because WordPress puts in the required rewrite rules.

To get it work in Nginx, you have to add the following config in the Nginx site configuration

Under the / location context, add the following

try_files $uri $uri/ /index.php?$args;

This is essentially telling Nginx to try to display the URI as is, and if it fails that, pass the URI as an argument to index.php.