Domainly
Technical Guide

Complete Guide to Custom Domain Management for SaaS Applications

Learn everything you need to know about implementing custom domains in your SaaS application, from DNS configuration to SSL certificates and multi-tenant architecture.

August 27, 2025
8 min read
Domainly Team

Table of Contents

Introduction to Custom Domains

Custom domain management is a crucial feature for modern SaaS applications that want to provide white-label solutions or allow customers to use their own branded domains. Instead of forcing users to access your service through generic subdomains like customer.yourapp.com, custom domains enable them to use their own domains like app.customer.com.

This comprehensive guide will walk you through everything you need to know about implementing custom domain management in your SaaS application, from the initial DNS configuration to advanced multi-tenant architecture patterns.

Benefits of Custom Domains

Brand Consistency

Customers can maintain their brand identity by using their own domain names, creating a seamless experience for their users.

Trust & Credibility

Custom domains increase user trust as customers see familiar domain names rather than third-party services.

SEO Benefits

Content served from custom domains can improve SEO rankings and help customers build domain authority.

Flexibility

Enables white-label solutions and allows customers to integrate your service seamlessly into their existing infrastructure.

Technical Requirements

Before implementing custom domain management, you need to understand the core technical components required:

  • DNS Management System: Ability to create and manage DNS records programmatically
  • SSL Certificate Provisioning: Automated SSL certificate generation and renewal
  • Reverse Proxy Configuration: Route requests from custom domains to your application
  • Domain Verification: Ensure customers own the domains they're trying to connect

DNS Configuration

DNS configuration is the foundation of custom domain management. Your customers need to point their domains to your infrastructure through DNS records.

CNAME vs A Records

CNAME Records (Recommended)

app.customer.com. CNAME proxy.yourservice.com.

CNAME records are preferred because they automatically inherit IP changes from your proxy server.

A Records (Alternative)

app.customer.com. A 192.0.2.1

A records point directly to IP addresses but require updates when IPs change.

SSL Certificate Management

SSL certificates are essential for custom domains to ensure secure HTTPS connections. Modern implementations should automate certificate provisioning and renewal.

Let's Encrypt Integration

Let's Encrypt provides free SSL certificates with automated renewal. Here's a basic flow:

  1. 1. Verify domain ownership through DNS or HTTP challenge
  2. 2. Request certificate from Let's Encrypt
  3. 3. Install certificate on your reverse proxy
  4. 4. Set up automatic renewal (certificates expire every 90 days)

Rate Limiting Considerations

Let's Encrypt has rate limits (50 certificates per domain per week). Plan for production usage and consider using staging environment for testing.

Domain Verification Process

Domain verification ensures that customers actually own the domains they're trying to connect. This prevents unauthorized domain hijacking and abuse.

Verification Methods

TXT Record Verification

Customer adds a TXT record with a unique verification token:

_domainly-verification.app.customer.com. TXT "verification-token-123"

HTTP File Verification

Customer uploads a file to their domain root:

http://app.customer.com/.well-known/domainly-verification.txt

Multi-Tenant Architecture

Multi-tenant architecture is crucial for SaaS applications supporting custom domains. You need to route requests to the correct tenant based on the incoming domain.

Tenant Resolution Strategies

Database Lookup

Store domain-to-tenant mappings in your database:

SELECT tenant_id FROM domains 
WHERE domain_name = 'app.customer.com' 
AND status = 'verified'

Redis Cache

Cache domain mappings for faster lookups:

// Cache key: domain:app.customer.com
// Value: tenant-id-123

Implementation Strategies

There are several approaches to implementing custom domain management, each with different trade-offs in complexity, cost, and maintenance.

1. Reverse Proxy Approach

Use a reverse proxy (Nginx, Caddy, HAProxy) to handle domain routing and SSL termination.

  • • ✅ Full control over routing logic
  • • ✅ Automated SSL certificate management
  • • ❌ Requires infrastructure management
  • • ❌ Complex configuration updates

2. CDN/Edge Network

Use services like Cloudflare, AWS CloudFront, or similar for domain management.

  • • ✅ Global edge locations
  • • ✅ Built-in DDoS protection
  • • ❌ Vendor lock-in
  • • ❌ Limited customization

3. Domain-as-a-Service

Use specialized services like Domainly for complete domain management.

  • • ✅ No infrastructure management
  • • ✅ Comprehensive APIs
  • • ✅ Faster time to market
  • • ❌ Third-party dependency

Best Practices

Security Considerations

  • • Always verify domain ownership before activation
  • • Implement rate limiting for domain verification attempts
  • • Use HTTPS-only policies for all custom domains
  • • Monitor for suspicious domain patterns

Performance Optimization

  • • Cache domain-to-tenant mappings
  • • Use HTTP/2 and modern protocols
  • • Implement proper CDN caching strategies
  • • Monitor SSL certificate expiration

User Experience

  • • Provide clear setup instructions
  • • Show real-time verification status
  • • Include troubleshooting guides
  • • Support both apex and subdomain configurations

Conclusion

Implementing custom domain management in your SaaS application is a complex but valuable feature that can significantly improve customer satisfaction and enable white-label solutions. The key is to start with a solid understanding of the technical requirements and choose an implementation strategy that fits your team's capabilities and business needs.

Whether you build your own solution or use a service like Domainly, focus on providing a seamless user experience with clear documentation, real-time status updates, and reliable automation. Remember that custom domains are often mission-critical for your customers, so invest in proper monitoring, security, and redundancy.

Ready to implement custom domains?

Domainly provides a complete domain management infrastructure that handles all the complexity for you. Get started with our simple APIs and have custom domains running in your SaaS in minutes.