From caccd81c3eb7954662d20cab10cc3afeeabca615 Mon Sep 17 00:00:00 2001
From: Christian Cleberg <hello@cleberg.net>
Date: Sat, 2 Dec 2023 11:23:08 -0600
Subject: initial commit

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++++
+date = 2022-12-07
+title = "Redirect Nginx Subdomains & Trailing Content with Regex"
+description= "You can easily redirect Nginx traffic from subdomains and TLDs to a new domain while preserving trailing content."
++++
+
+## Problem
+
+I recently migrated domains and replaced the
+old webpage with a simple info page with instructions to users on how
+to edit their bookmarks and URLs to get to the page they were seeking.
+
+This was not ideal as it left the work up to the user and may have caused
+friction for users who accessed my RSS feed.
+
+## Solution
+
+Instead, I finally found a solution that allows me to redirect both subdomains
+AND trailing content. For example, both of these URLs now redirect properly
+using the logic I'll explain below:
+
+```txt
+# Example 1 - Simple base domain redirect with trailing content
+https://domain1.com/blog/alpine-linux/ -> https://domain2.com/blog/alpine-linux/
+
+# Example 2 - Complex redirect with both a subdomain and trailing content
+https://libreddit.domain1.com/r/history/comments/7z8cbg/new_discovery_mode_turns_video_game_assassins/
+->
+https://libreddit.domain2.com/r/history/comments/7z8cbg/new_discovery_mode_turns_video_game_assassins/
+```
+
+Go ahead, try the URLs if you want to test them.
+
+### Nginx Config
+
+To make this possible. I needed to configure a proper redirect scheme in my
+Nginx configuration.
+
+```sh
+doas nano /etc/nginx/http.d/domain1.conf
+```
+
+Within this file, I had one block configured to redirect HTTP requests to HTTPS 
+for the base domain and all subdomains.
+
+```conf
+server {
+        listen [::]:80;
+        listen 80;
+        server_name domain1.com *.domain1.com;
+
+        if ($host = domain1.com) {
+                return 301 https://$host$request_uri;
+        }
+
+        if ($host = *.domain1.com) {
+                return 301 https://$host$request_uri;
+        }
+
+        return 404;
+}
+```
+
+For the base domain, I have another `server` block dedicated to redirecting all
+base domain requests. You can see that the `rewrite` line is instructing Nginx
+to gather all trailing content and append it to the new `domain2.com` URL.
+
+```conf
+server {
+        listen [::]:443 ssl http2;
+        listen 443 ssl http2;
+
+        server_name domain1.com;
+
+        rewrite ^/(.*)$ https://domain2.com/$1 permanent;
+
+        ssl_certificate     /etc/letsencrypt/live/domain1.com/fullchain.pem;
+        ssl_certificate_key /etc/letsencrypt/live/domain1.com/privkey.pem;
+}
+```
+
+Finally, the tricky part is figuring out how to tell Nginx to redirect while
+keeping both a subdomain and trailing content intact. I found that the easiest
+way to do this is to give it a `server` block of its own.
+
+Within this block, we need to do some regex on the `server_name` line before we
+can rewrite anything. This creates a variable called `subdomain`.
+
+Once the server gets to the `rewrite` line, it pulls the `subdomain` variable
+from above and uses it on the new `domain2.com` domain before appending the
+trailing content (`$request_uri`).
+
+```conf
+server {
+        listen [::]:443 ssl http2;
+        listen 443 ssl http2;
+
+        server_name ~^(?<subdomain>\w+)\.domain1\.com$;
+
+        rewrite ^ https://$subdomain.domain2.com$request_uri permanent;
+
+        ssl_certificate     /etc/letsencrypt/live/domain1.com/fullchain.pem;
+        ssl_certificate_key /etc/letsencrypt/live/domain1.com/privkey.pem;
+}
+```
+
+That's all there is to it. With this, I simply restarted Nginx and watched the
+redirections work in-action.
+
+```sh
+doas rc-service nginx restart
+```
+
+
+Looking back on it, I wish I had done this sooner. Who knows how many people
+went looking for my sites or bookmarks and gave up when they saw the redirect
+instructions page.
+
+Oh well, it's done now. Live and learn.
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