How can I support dynamic custom subdomains (CNAMEs) pointing to my Railway app?
manojnaidu619
PROOP

4 months ago

I’m building a multi-tenant SaaS app, and I need help figuring out how to handle dynamic custom subdomains.

Here’s the situation:

  • My main web app is hosted on a custom domain connected to Railway, for example:

    app.myapp.com

  • I’d like my users to be able to connect their own subdomains to it, like:

    dashboard.customer.com → CNAME → app.myapp.com

  • When someone visits dashboard.customer.com, I want Railway to serve the same app (my backend detects the tenant based on the Host header).

Right now, if I try this, I get the “Train has not arrived at the station” message — which I understand means Railway doesn’t recognize the domain until it’s manually added under Settings → Networking → Custom Domains.

That works for testing, but in production this won’t scale. I need a setup where customers can connect their own subdomains automatically (like other SaaS platforms that use wildcard or dynamic domain mapping).

So my questions are:

  1. Does Railway support dynamic custom domains - so any CNAME pointing to my base domain is accepted automatically?

  2. If not, is there an API or programmatic way to register new custom domains from my app when a customer adds theirs?

I’m basically trying to let customers point subdomain.theirdomain.com → app.myapp.com and have it just work, without manually adding every new domain inside Railway.

Thanks so much for any clarification or suggestions! pray emoji

$30 Bounty

4 Replies

Railway
BOT

4 months ago

Hey there! We've found the following might help you get unblocked faster:

If you find the answer from one of these, please let us know by solving the thread!

manojnaidu619
PROOP

3 months ago

Any update on this please? I'm stuck.

callmeal3x
PRO

3 months ago

Hey! I found out your question was interesting, so here is my answer :

Option 1: Wildcard Subdomains (What I Use)

Just add *.myapp.com in Railway → Settings → Custom Domains

DNS Setup:

*.myapp.com  →  CNAME  →  <your-railway-domain>.up.railway.app
*.myapp.com  →  CNAME  →  authorize.railwaydns.net

Important: If you're using Cloudflare, make sure authorize.railwaydns.net is DNS-only (gray cloud, not proxied).

In my app:

const host = req.headers.host; // "customer1.myapp.com"
const tenant = host.split('.')[0]; // "customer1"

That's it! Now customer1.myapp.com, customer2.myapp.com, etc. all work without touching Railway again.

Option 2: True Custom Domains (Their Own Domain)

If customers want dashboard.customer.com pointing to your app, you'll need to use Railway's API:

const addCustomDomain = async (domain) => {
  await fetch('https://backboard.railway.app/graphql/v2', {
    method: 'POST',
    headers: {
      'Authorization': `Bearer ${process.env.RAILWAY_API_TOKEN}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      query: `mutation customDomainCreate($input: CustomDomainCreateInput!) {
        customDomainCreate(input: $input) { id domain status }
      }`,
      variables: {
        input: {
          domain,
          serviceId: process.env.RAILWAY_SERVICE_ID,
          environmentId: process.env.RAILWAY_ENVIRONMENT_ID
        }
      }
    })
  });
};

The flow: customer enters their domain → my backend calls Railway API → customer adds the CNAME → Railway handles SSL automatically.

My recommendation: Start with wildcards. It's zero maintenance and scales perfectly. Only add the API integration if customers really need their own branded domains.

Check out the docs here: https://docs.railway.com/guides/public-networking#wildcard-domains

Hope this helps! pray emoji

callmeal3x

Hey! I found out your question was interesting, so here is my answer :Option 1: Wildcard Subdomains (What I Use)Just add *.myapp.com in Railway → Settings → Custom DomainsDNS Setup:*.myapp.com → CNAME → <your-railway-domain>.up.railway.app *.myapp.com → CNAME → authorize.railwaydns.netImportant: If you're using Cloudflare, make sure authorize.railwaydns.net is DNS-only (gray cloud, not proxied).In my app:const host = req.headers.host; // "customer1.myapp.com" const tenant = host.split('.')[0]; // "customer1"That's it! Now customer1.myapp.com, customer2.myapp.com, etc. all work without touching Railway again.Option 2: True Custom Domains (Their Own Domain)If customers want dashboard.customer.com pointing to your app, you'll need to use Railway's API:const addCustomDomain = async (domain) => { await fetch('https://backboard.railway.app/graphql/v2', { method: 'POST', headers: { 'Authorization': `Bearer ${process.env.RAILWAY_API_TOKEN}`, 'Content-Type': 'application/json', }, body: JSON.stringify({ query: `mutation customDomainCreate($input: CustomDomainCreateInput!) { customDomainCreate(input: $input) { id domain status } }`, variables: { input: { domain, serviceId: process.env.RAILWAY_SERVICE_ID, environmentId: process.env.RAILWAY_ENVIRONMENT_ID } } }) }); };The flow: customer enters their domain → my backend calls Railway API → customer adds the CNAME → Railway handles SSL automatically.My recommendation: Start with wildcards. It's zero maintenance and scales perfectly. Only add the API integration if customers really need their own branded domains.Check out the docs here: https://docs.railway.com/guides/public-networking#wildcard-domainsHope this helps!

manojnaidu619
PROOP

2 months ago

hey, thanks for the detailed response. But how many entries can I add through railway API? I'm sure there's a very small limit.

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