Custom Domains for SaaS: A Practical Guide

As your SaaS product gains traction and usage increases, some customers will eventually ask for one thing:

Can I use my own domain?

It usually starts with your bigger accounts. Then everyone else wants it too.

Custom domains are not just a branding feature. For many SaaS products, especially when your competitors offer custom domains, they are table stakes. But implementing them is more involved than adding a field called custom_domain to your database.

Interested in a straightforward solution for custom domain implementation in your SaaS? Try hostgrid for a seamless experience.

This guide walks through how custom domains actually work, what breaks at scale, and how to think about building it into your SaaS product.

Why SaaS Companies Add Custom Domains

Your customers want control over their brand.

If you run a white-label platform, a site builder, a client portal, or a multi-tenant dashboard, your customers don’t want URLs like:

customer.yourapp.com

They want:

app.customer.com
portal.customer.com
customer.com

There are practical reasons too:

• Brand consistency – everything lives under their domain.
• Trust – users are more comfortable on a familiar URL.
• Email deliverability – links in transactional emails match the sender’s domain.
• White-labeling – agencies and platforms can resell your product as their own.

Once you support custom domains, your product feels like “infrastructure”, not a replaceable tool. Infrastructure is sticky—customers rarely change DNS records once it’s live, especially when updates require internal review or approval. That friction makes your product much harder to swap out.

Step 1: How Traffic Reaches Your App

At a basic level, a custom domain is just DNS pointing to your infrastructure.

Your customer updates their DNS records so that:

• app.customer.com points to your service
• Or customer.com (apex/root) points to your service

There are two common approaches.

CNAME (Subdomains)

For subdomains like app.customer.com, customers usually create a CNAME record that points to something you control:

app.customer.com → your-proxy.yourapp.com

This is the cleanest setup. It avoids hardcoding IP addresses and gives you flexibility.

A Record (Root Domain)

If they want the root domain (customer.com), they often need an A record that points to an IP address.

This creates a problem:

If that IP ever changes, every customer’s DNS breaks, and traffic stops getting routed to your SaaS product, essentially a blackout.

Some DNS providers support CNAME-like behavior at the root using flattening, but you cannot assume all customers use the same DNS provider.

As your SaaS grows, DNS edge cases multiply. You need to design for them early.

Step 2: HTTPS Is Not Optional

Pointing DNS is only half the job.

If someone visits app.customer.com and you do not have a valid SSL certificate for that domain, the browser blocks access with a security warning.

That means you must:

1. Verify the domain
2. Issue a certificate
3. Renew it automatically
4. Attach it to your edge or proxy layer

Most SaaS teams use a certificate authority like Let’s Encrypt and automate issuance through ACME.

This works well for a handful of domains.

It gets harder when you manage hundreds or thousands.

You now need to handle:

• Failed validations
• Expiring certificates
• Rate limits from the certificate authority
• Retry logic
• Monitoring and alerts

If certificates stop renewing, your customers find out before you do, because your SaaS product stops working on their custom domain. Once again, a blackout situation!

Step 3: You Need a Smart Backend Edge Layer

To support custom domains properly, you usually place a reverse proxy or edge layer in front of your app.

That layer:

• Terminates TLS (handles HTTPS)
• Routes traffic to the correct tenant
• Forwards the original Host header
• Applies certificates dynamically

Your application must identify tenants based on the domain in the request.

A typical flow looks like this:

1. Request hits your proxy.
2. Proxy handles TLS.
3. Proxy forwards request with original host.
4. Your app reads the host and maps it to a customer account.

If that mapping fails, you should not serve default content. You should block or return a clear error. Otherwise, you risk leaking data across tenants.

Multi-tenant routing is simple in theory and sensitive in practice.

Step 4: Verification Before Activation

One mistake many SaaS teams make: activating domains before verifying ownership.

You should only activate a custom domain after you confirm the user controls it.

Common verification approaches:

• DNS TXT record verification
• CNAME validation
• HTTP challenge (for certificate issuance)

A safe flow looks like this:

1. Customer submits domain.
2. You generate verification instructions.
3. You check DNS.
4. You issue SSL.
5. You activate the domain.

Until verification succeeds, the domain should not serve production traffic.

This protects you from misconfigurations and malicious attempts.

Step 5: What Changes at Scale

Supporting 5 custom domains is one thing.

Supporting 5,000 is another.

At scale, you start dealing with:

• DNS propagation delays across regions
• Certificate authority rate limits
• Burst traffic during domain launches
• Customers who misconfigure DNS and blame you
• The need for high availability at the edge

You also need observability:

• Which domains are active?
• Which are pending verification?
• Which certificates expire soon?
• Which upstream service does each domain map to?

Without clear domain lifecycle management, support tickets grow quickly.

Build It Yourself or Use Infrastructure?

You can build all of this in-house. Many teams do.

But it requires ongoing maintenance. Custom domains are not a one-time feature. They become a permanent infrastructure responsibility.

An alternative is to use a dedicated domain layer that handles:

• DNS verification
• SSL provisioning and renewal
• Safe activation after verification
• Routing domains to your upstream application

At hostgrid, Our approach is to provide custom domains for any platform.

For SaaS teams, we offer:

• Developer API – programmatic domain provisioning
• Automatic SSL
• DNS verification
• Domain activation only after verification

We focus only on the domain layer. Your upstream application stays exactly as it is. We do not modify your content or inject anything into responses.

If you prefer to own everything, this guide should help you design it correctly. If you would rather not maintain certificate automation and edge routing forever, using a dedicated system can simplify your stack.

Common Questions SaaS Teams Ask

Can I map a custom domain to a specific path? Path-based mapping (for example, app.customer.com → yourapp.com/customer-123) is available.

Does this work with any hosting provider? Yes. As long as your upstream is reachable, the domain layer can sit in front of it.

Do I need to change my backend? Your application must support tenant routing by domain. Beyond that, no structural changes are required.

Final Thoughts

Custom domains feel simple from the outside. Inside a SaaS architecture, they touch DNS, TLS, routing, and multi-tenant isolation.

If you plan to offer white-labeling or serve serious customers, you will likely need them.

Design the system carefully. Automate everything you can. Never activate a domain before you verify it. Monitor certificate renewals like production infrastructure, because that is exactly what they are.

If you are building a multi-tenant SaaS and want to offer custom domains without owning the entire certificate and DNS lifecycle, you can apply for early API access and we can walk through your use case.