The difference between `return` and `rewrite` in Nginx and their syntax

Actually, I hadn’t paid much attention to `return` and `rewrite` before, because I always used one-click scripts, and I just used whatever the script used. It wasn’t until I was working on SSL certificate domain redirection these past few days that I started to learn about them.

In Nginx, both `return` and `rewrite` are used for redirecting requests, but there are differences, and their syntax is different.

1. Differences between `return` and `rewrite`
Execution Method:

`return`: Immediately terminates the current request processing flow and returns the specified HTTP status code and response headers. It is processed internally by Nginx and does not send an additional request to the client.

`rewrite`: Rewrites the request URI and makes a new request based on the new URI. It is performed between the client and server and will trigger an additional request-response round trip.

Purpose:

`return` is typically used to implement HTTP redirects (301, 302, etc.) and set specified HTTP response codes. It is usually more lightweight and suitable for simple redirection needs.

`rewrite` is used to modify the request URI more flexibly and can rewrite the URI based on complex conditions. It can also redirect requests internally to different handlers or location blocks.

Performance: `return` is more efficient than `rewrite` because it processes requests internally within Nginx and doesn’t cause additional request-response round trips.

`rewrite` causes additional request-response round trips, therefore its performance is slightly worse than `return`.

For simple redirection needs, `return` is recommended. For more complex URI rewriting logic, `rewrite` can be used.

2. `return` and `rewrite` syntax

Basic `return` rule syntax:

`return [HTTP response code] [URL];`
For example, to perform a permanent redirect (301), the syntax is:

`return 301 http://example.com/new-url;`

Basic `rewrite` syntax is as follows:

`rewrite [regular expression] [target address] [options];`
For example, to rewrite all requests to a single PHP file, the syntax is:

`rewrite ^(.*)$ /index.php?$query_string last;`
Here, `^(.*)$` is the regular expression, `/index.php?$query_string` is the target address, and `last` is an option indicating that this is the last `rewrite` directive.

`return` is used to terminate the request and send a response, typically used for redirection; `rewrite` is used to modify the request URI and redirect the request to another address, typically used for URL rewriting or internal forwarding.

Therefore, for 301 redirects, `return` is more suitable, while `rewrite` is suitable for internal link forwarding.