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+#+title: Redirect Nginx Subdomains & Trailing Content with Regex
+#+date: 2022-12-07
+#+description: A simple Nginx configuration to redirect all subdomains and trailing content.
+#+filetags: :nginx:
+
+* 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:
+
+#+begin_src 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/
+#+end_src
+
+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.
+
+#+begin_src sh
+doas nano /etc/nginx/http.d/domain1.conf
+#+end_src
+
+Within this file, I had one block configured to redirect HTTP requests
+to HTTPS for the base domain and all subdomains.
+
+#+begin_src 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;
+}
+#+end_src
+
+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.
+
+#+begin_src conf
+server {
+        listen [::]:443 ssl http2;
+        listen 443 ssl http2;
+
+        server_name domain1.com;
+
+        rewrite ^/(.*)$ https://domain2.com/$1 permanent;
+
+        ssl_certificate     /etc/letsencrypt/live/domain1.com/fullchain.pem;
+        ssl_certificate_key /etc/letsencrypt/live/domain1.com/privkey.pem;
+}
+#+end_src
+
+Finally, the tricky part is figuring out how to tell Nginx to redirect
+while keeping both a subdomain and trailing content intact. I found that
+the easiest way to do this is to give it a =server= block of its own.
+
+Within this block, we need to do some regex on the =server_name= line
+before we can rewrite anything. This creates a variable called
+=subdomain=.
+
+Once the server gets to the =rewrite= line, it pulls the =subdomain=
+variable from above and uses it on the new =domain2.com= domain before
+appending the trailing content (=$request_uri=).
+
+#+begin_src 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;
+}
+#+end_src
+
+That's all there is to it. With this, I simply restarted Nginx and
+watched the redirections work in-action.
+
+#+begin_src sh
+doas rc-service nginx restart
+#+end_src
+
+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.