Blog · Explainer
How custom domains work: DNS in plain English.
A custom domain works by adding a DNS record that points your hostname to the server or platform hosting your app. For platforms, that record is usually a CNAME; once it resolves, the platform issues an HTTPS certificate for your domain.
- DNS is the internet's phone book
- A CNAME points one name at another
- Apex domains need ALIAS or flattening
- HTTPS is issued after DNS resolves
DNS
What is DNS?
DNS (Domain Name System) translates domain names into the addresses computers connect to. The custom domain setup guide shows the exact record Runex needs.
When someone visits app.example.com, their browser asks a DNS resolver where that name lives. The answer comes from records you set at your DNS provider.
Changing those records is how you point a domain at a new host, no change on the visitor's side.
Compare
A record vs CNAME: what's the difference?
An A record points to an IP address; a CNAME points to another name.
| Name → nameCNAME | Name → IPA record | |
|---|---|---|
| Points to | Another hostname | An IPv4 address |
| Example value | cname.runex.cloud | 203.0.113.10 |
| If the host's IPs change | Keeps working | You must update it |
| Allowed at the apex | No (use ALIAS / flattening) | Yes |
HTTPS
How does HTTPS work on a custom domain?
The platform proves it controls the domain, then issues a certificate. On Runex this happens on its own through automatic SSL.
-
You
Add the CNAME
Point the hostname at the platform.
-
DNS
Propagate
Resolvers learn the new record.
-
Platform
Verify
Confirms the name resolves to it.
-
Platform
Issue HTTPS
Certificate issued and auto-renewed.
Example
Example: pointing app.acme.com at Runex
One record, one dashboard entry. If the domain still won't load, work through the custom domain troubleshooting checklist.
- Deploy the app: it's live at acme.runex.cloud
- At the DNS provider: CNAME app → cname.runex.cloud
- In Runex: attach app.acme.com to the app
- DNS propagates; Runex issues the certificate
- https://app.acme.com serves the app
Type CNAME Name app Value cname.runex.cloud TTL 300
FAQ
Frequently asked questions
Short answers to related searches.
What is a CNAME record?
A DNS record that makes one hostname an alias of another. For example, app.example.com can be a CNAME of cname.runex.cloud. The custom domain setup guide shows the exact record to add.
What is the difference between an apex domain and a subdomain?
The apex is the bare domain, like example.com. A subdomain adds a label in front, like app.example.com or www.example.com.
Why can't I use a CNAME on my root domain?
DNS rules don't allow a CNAME alongside the other records the apex must have. Providers offer ALIAS, ANAME, or CNAME flattening instead.
What is TTL in DNS?
Time to live: how many seconds resolvers may cache a record. A lower TTL makes future changes spread faster. If a change still has not taken effect, use the custom domain troubleshooting checklist.
Next step
Put it into practice.
Deploy an app from GitHub on Runex and get a live HTTPS URL. Free to start.