How Nginx Chooses Which Location to Use to Handle Requests

Nginx begins by checking all prefix-based location matches (all location types not involving a regular expression). It checks each location against the complete request URI.
First, Nginx looks for an exact match. If a location block using the = modifier is found to match the request URI exactly, this location block is immediately selected to serve the request.
If no exact (with the = modifier) location block matches are found, Nginx then moves on to evaluating non-exact prefixes. It discovers the longest matching prefix location for the given request URI, which it then evaluates as follows:
- If the longest matching prefix location has the ^~ modifier, then Nginx will immediately end its search and select this location to serve the request.
- If the longest matching prefix location has the ^~ modifier, then Nginx will immediately end its search and select this location to serve the request.
After the longest matching prefix location is determined and stored, Nginx moves on to evaluating the regular expression locations (both case sensitive and insensitive). Nginx tries the regular expression locations sequentially. The first regular expression location that matches the request URI is immediately selected to serve the request.
If no regular expression locations are found that match the request URI, the previously stored prefix location is selected to serve the request.

It is important to understand that, by default, Nginx will serve regular expression matches in preference to prefix matches. However, it evaluates prefix locations first, allowing for the administer to override this tendency by specifying locations using the = and ^~ modifiers.

It is also important to note that, while prefix locations generally select based on the longest, most specific match, regular expression evaluation is stopped when the first matching location is found. This means that positioning within the configuration has vast implications for regular expression locations.