If you have a Synology DiskStation and already have a hostname (for your website, blog, or other) you can set up your DiskStation on a dedicated subdomain easily — even if you have a dedicated IP address.
First, determine what subdomain you’re going to assign to your device, based on the domain name you already have. For example, you might own example.com and want ds.example.com to point to your DiskStation. That’s perfectly fine — it’s your choice.
Next, get yourself a free dynamic IP hostname at a service like DynDNS. They provide Dynamic DNS hosts for free, and it only takes a few minutes to sign up. It doesn’t matter what domain you pick, but you only get one. For the purpose of this guide, I’ll say that I signed up for example.dyndns.org. If you are using the Synology Dynamic DNS service, you have this already. Continue.
Once you’re signed up and activated your domain, you need to set up automatic updating. You can do this through the DiskStation itself under Control Panel > DDNS, or with a router that supports Dynamic IP updating (most routers).
Now your client will keep your hostname up to date automatically, even if your IP address changes.
The next step is to assign your new DynDNS hostname to a DNS CNAME record. You want to add a CNAME record for ds.example.com that points to example.dyndns.org. Specific instructions will vary by your DNS registrar, so consult them if you’re not sure exactly how to add the record. Keep in mind it may take up to 24+ hours for the DNS record to propagate, so if it doesn’t work right away, try again later.
Once the DNS zone has propagated, you should be able to access your DiskStation at your new hostname ds.example.com, and the DynDNS client will keep your hostname updated.
If you want to create an SSL cert for HTTPS access, create it for ds.example.com using the instructions found here: https://mikebeach.org/2012/11/13/startssl-ssl-certificate-on-synology-nas-using-subdomain
Questions, comments, and feedback about this are welcome.