Add document "How to set up an application proxy in Nginx?"

Author: Jonathan Visser

docs/hypernode-platform/nginx/how-to-set-up-an-application-proxy-nginx.md

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+---
+myst:
+  html_meta:
+    description: Learn how to set up an Nginx application proxy on Hypernode using Managed Vhosts: create a proxy vhost and point it to your app
+    title: How to set up an application proxy in Nginx? | Hypernode
+---
+
+# How to Set Up an Application Proxy in Nginx
+
+Sometimes you want to serve an application that listens on a local port (for example a Node, Python or PHP service on `localhost:3000`) behind a friendly domain on your Hypernode. Instead of writing a custom Nginx config, you can use Hypernode Managed Vhosts to generate a ready‑made proxy vhost coniguration and then just point it to your application. This keeps your configuration simple and consistent with the rest of your setup.
+
+## Create a proxy vhost
+
+Create a new vhost and set its type to `proxy`. In the example below we create a vhost for `proxy.myapp.hypernode.io`:
+
+```bash
+app@abc123-myapp-magweb-cmbl:~$ hmv proxy.myapp.hypernode.io --type proxy
+INFO: Managing configs for proxy.myapp.hypernode.io
+INFO: No existing config for proxy.myapp.hypernode.io, starting with default options
+INFO: Writing HTTP config for proxy.myapp.hypernode.io
+```
+
+This command creates a vhost directory under `/data/web/nginx/<your-domain>/` with the proxy templates. You will see the following files:
+
+```bash
+app@abc123-myapp-magweb-cmbl:~/nginx/proxy.myapp.hypernode.io$ ls
+public.proxy.conf  server.rewrites.conf  staging.proxy.conf
+```
+
+## Point the proxy to your application
+
+Open `public.proxy.conf`. The only lines you normally need to change are at the top: the upstream host and port your application listens on. By default they point to `localhost:3000`.
+
+```nginx
+app@abc123-app-magweb-cmbl:~/nginx/proxy.myapp.hypernode.io$ cat public.proxy.conf
+set $app_proxy_host localhost;
+set $app_proxy_port 3000;
+
+root /data/web/public;
+
+include /etc/nginx/app_proxy_handler.conf;
+
+location / {
+    echo_exec @app_proxy_handler;
+}
+```
+
+Replace `localhost` and `3000` with the correct target for your app if it listens elsewhere. You generally do not need to change anything below those two lines. The included `app_proxy_handler.conf` wires up sensible proxy defaults, SSL, headers and buffering for you. Save the file and Nginx will apply the change.
+
+If you also plan to use the staging mode of this vhost, mirror the same host and port settings in `staging.proxy.conf` so that the staging switch serves the same upstream.