What are the steps to point multiple domains to the same IP address?

What should you do if you want different domain names to access the same website and the same server? Regardless of the reason, resolving multiple domain names to the same IP address is technically straightforward and standard. The key lies in understanding and correctly configuring DNS records.

The most basic and commonly used method is to set up a separate A record for each domain name. An A record is the most basic record type in DNS; it directly maps a domain name (or subdomain) to an IPv4 address. You don't need any complex associations; simply create an A record pointing to the target server's IP address in the DNS management console for each domain.

The process is usually consistent: Log in to your domain registrar or DNS service provider's management platform (such as Alibaba Cloud, Cloudflare, Namecheap, etc.), find the domain name you need to configure, and enter the DNS resolution management interface. Add a new record, selecting type "A". In the "Host Record" or "Name" field, enter your desired subdomain (e.g., to point the root domain `example.com` to the IP address, enter `@` or leave it blank; to point `www.example.com` to the IP address, enter `www`). Then, accurately enter the server's public IP address (e.g., `192.0.2.1`) in the "Record Value" or "Destination Address" field. Finally, set an appropriate TTL (Time To Live) and save.

Suppose you have three domains: `domain1.com`, `domain2.net`, and `brand-site.org`, and you need to point them all to the server IP `203.0.113.10`. You only need to complete the above steps of adding A records in the DNS settings of each of the three domains. After completion, the global DNS system will gradually update, and eventually all three domains will be redirected to the same server.

To support both IPv4 and IPv6 access simultaneously, you also need to add an AAAA record for each domain. The principle is the same as an A record, except the record value needs to be the server's IPv6 address. Furthermore, for user convenience, it's common practice to add corresponding A records for each `www` subdomain (e.g., `www.domain1.com`), pointing to the same IP address. A more efficient approach is to set the `www` subdomain as a CNAME record, pointing to its root domain (e.g., making `www.domain1.com` an alias of `domain1.com`). This way, when the root domain IP changes, only one A record needs to be modified.

Resolving a domain name to an IP address only completes the "addressing" process. Once all traffic reaches the server, a crucial question arises: how does the server know which domain the user initially accessed? This is critical because websites need to display different content based on different domains, or at least respond correctly. This problem is solved at the HTTP protocol layer. When a browser initiates a request, it includes a `Host` field in the HTTP request header, explicitly informing the server which domain the request is for. Modern web servers (such as Nginx and Apache) rely on the `Host` header to differentiate requests and process them accordingly.

Therefore, you must explicitly tell your web server in its configuration: "Listen to this IP address and distribute requests to the appropriate website directory or application based on the different `Host` headers." Below is a configuration example of an Nginx server that listens on port 80 in a server block (virtual host) and lists all the domains it should respond to using the `server_name` directive:

nginx

server {

listen 80; # Listen on port 80 for IPv4

listen [::]:80; # Listen on port 80 for IPv6

server_name domain1.com www.domain1.com domain2.net www.domain2.net brand-site.org www.brand-site.org;

# Root directory of the website

root /var/www/your-website;

index index.html index.htm;

# Other general configurations...

location / {

try_files $uri $uri/ =404;

}

}

This configuration allows Nginx to recognize requests for any of the domains in the list and respond with the contents of the `/var/www/your-website` directory. If you need different domains to display completely different websites, you need to configure multiple independent `server` blocks, each with its own unique `server_name` and `root` directory, but they can still listen on the same IP address.

Today, a complete solution must include HTTPS. When multiple domains resolve to the same IP and use HTTPS, you need to configure a valid SSL certificate for each domain. There are two main approaches: the first is to purchase and deploy a separate certificate for each domain; the second is to use a single SAN certificate that supports multiple domains (also known as a unified communications certificate), or a wildcard certificate (if the domains are subdomains of the same main domain, such as `a.site.com` and `b.site.com`). The most convenient and cost-effective solution is to use automated services provided by free certificate authorities such as Let's Encrypt. Their tools (like Certbot) can automatically request and deploy a certificate containing all `server_name`s listed in the Nginx configuration. Below is an example snippet of an Nginx configuration with SSL enabled:

nginx

server {

listen 443 ssl http2;

listen [::]:443 ssl http2;

server_name domain1.com www.domain1.com domain2.net;

# SSL certificate configuration

ssl_certificate /etc/letsencrypt/live/domain1.com/fullchain.pem;

ssl_certificate_key /etc/letsencrypt/live/domain1.com/privkey.pem;

# Other website configurations...

root /var/www/your-website;

index index.html;

}

In practice, some optimizations and pitfalls also need to be considered. To improve performance, you can deploy a CDN globally. In this case, your domain name no longer resolves directly to the origin server IP, but instead to a CNAME address provided by the CDN service provider. CDN edge nodes will retrieve content from the origin server on your behalf. This process is transparent to both users and the server, but it is essentially still a "multiple domains to a single backend" model.

Another important consideration is search engine optimization (SEO). If multiple domains have identical content, search engines may classify them as duplicate content, thus affecting rankings. If you want them to exist independently, you must return completely different website content on the server side based on the accessed domain. If it's just a redirect relationship, it's recommended to use an HTTP 301 permanent redirect to redirect the secondary domain to the primary domain, and use a `rel="canonical"` link tag to explicitly tell the search engine which is the primary version.

In summary, resolving multiple domain names to a single IP address is a complete operation that requires coordination from the network layer to the application layer: at the DNS layer, an A record (or CNAME record) is set up independently for each domain name; at the server layer, the web server's virtual host is configured correctly to ensure that it can recognize and handle requests from all target domain names; at the security layer, the appropriate SSL certificates are deployed for all domains that have HTTPS enabled.