To set up a reverse proxy in Synology DSM, the knowledge base says to use Reverse Proxy and create a rule with Source and Destination settings:
1. Click Reverse Proxy > Create and specify the rule in the General page.
2. Set:
- Protocol: HTTP or HTTPS
- Hostname: the source/destination device name
- Port: the source/destination port
- Enable HSTS (only for the source), or choose an Access control profile
3. Click Save.
You can create multiple reverse proxy rules, and later use Edit or Delete to change them.
The knowledge base also says you can add:
- Custom Header via Reverse Proxy > Create > Custom Header
- WebSocket via Create > WebSocket
For access via a subdomain with HTTPS, the fragments do not give a full subdomain-specific example, but they do show that DSM reverse proxy rules use hostname, port, and HTTPS on the source side. One forum fragment also mentions using reverse proxy with headers like X-Forwarded-Proto https, X-Forwarded-Host, and proxy_pass, but that is a community example rather than an official step-by-step DSM setup.
Sources used: [13], [9]