Made the data folder an envvar

nginx/subdomains_and_reverse_proxy.md

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+# Subdomain and reverse proxy
+
+Now that I have my own domain, life is pretty cool. I can leave behind the
+harsh days of typing my server IPs in the browser, and point to my services
+with nice names.
+
+Through porkbun's UI, I can point my domain name to any ip. But, I can't
+specify anything related to ports! After some research, I found out what I
+could do is to specify different subdomains in porkbun, and set up a reverse
+proxy in nginx to direct traffic thanks to this subdomains. Basically, I tell
+porkbun to direct each subdomain to my IP, and then I set up the nginx running
+in navaja to point to different docker containers depending on the subdomain
+that is getting requested.
+
+This is an example on how to set the reverse proxy config in nginx:
+
+```
+    server {
+        listen 80;
+        server_name git.contrapeso.xyz;
+        location / {
+            proxy_set_header Host $host;
+            proxy_pass       http://gogs_web_1:3000;
+            proxy_redirect off;
+        }
+    }
+```
+
+Where `git.contrapeso.xyz` is the subdomain and the contents of `proxy_pass` is
+where requests should be redirected.
+
+Something not obvious to take into account: since my nginx is running within a
+docker container, networking within navaja is a bit tricky. The way I got it
+right is to:
+
+- Make sure that the nginx container is running in the same network as the one
+  where traffic should be redirected.
+- Redirect using the container name and the listening port _within_ the
+  container, not the redirecting one in the host.