How to Fix a Subdomain Pointing to the Main Domain on Nginx or Apache

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If sub.example.com displays the website for example.com, DNS is usually only half of the configuration. The subdomain may correctly resolve to the server’s IP address, but Nginx or Apache is not matching the request’s hostname to a dedicated virtual host. An unmatched request is then handled by the default or first-listed site.

Fix it by checking DNS, creating an exact hostname match for the subdomain on the required port, configuring HTTPS separately when applicable, checking for application-level redirects, and testing with an explicit hostname and SNI request.

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What “pointing to the main domain” actually means

A DNS record does not select a website directory or application. It only tells a browser where to send the request. It is perfectly normal for the root domain and several subdomains to resolve to the same IPv4 address, IPv6 address, or load balancer.

After DNS resolution, the web server chooses a virtual host using the hostname supplied by the client:

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1. For ordinary HTTP, the browser sends a Host value such as sub.example.com.
2. For HTTPS, the TLS handshake uses the Server Name Indication (SNI) hostname before the encrypted HTTP request is processed.
3. Nginx or Apache compares that name with its configured virtual hosts and serves a document root or proxy target.

If no matching host exists, Nginx routes the request to the default server for that port. Apache commonly uses the first listed virtual host for the matching address and port. That fallback is why a subdomain can show the main site even though its DNS record is correct.

Start with a short diagnosis

1. Verify DNS before changing the web server

Check the subdomain’s A, AAAA, or CNAME record and confirm that it ultimately reaches the server, load balancer, or reverse proxy intended to host the subdomain. Test from a resolver that is not affected by your local cache, and check both IPv4 and IPv6 if both records exist.

A record that resolves to the same address as the main domain is not an error. The important questions are whether the address is correct and whether an unexpected AAAA record sends some clients to a different machine.

• Inspect the A record with dig sub.example.com A or an equivalent DNS lookup tool.
• Inspect IPv6 with dig sub.example.com AAAA. Remove or correct an AAAA record if the IPv6 endpoint is not configured with the same virtual host.
• Follow a CNAME to its final address and verify that the target is the service you intend to use.
• Check the authoritative DNS zone if public resolvers return different answers during a recent change; TTL caching can make old data persist temporarily.

Apache’s virtual-host guidance describes the relationship directly: map each hostname to the correct IP in DNS, then configure Apache to recognize the different hostnames. DNS alone cannot choose between two websites on one listener.

2. Fix Nginx hostname matching

Create a dedicated HTTP server block

Give the subdomain its own server block. Use the exact fully qualified name and point it to the correct static directory or upstream application.

server {
    listen 80;
    server_name sub.example.com;

    root /var/www/sub.example.com;
    index index.html;
}

For a reverse-proxied application, replace the static-file directives with the intended upstream, for example:

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server {
    listen 80;
    server_name sub.example.com;

    location / {
        proxy_pass http://127.0.0.1:3000;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-Host $host;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_set_header X-Real-IP $remote_addr;
    }
}

The upstream port and header policy must match your application. Do not copy the main domain’s proxy target merely because the two names share an IP address.

Keep the main site’s name list exclusive

Inspect every enabled Nginx configuration. The main site should list only names that are supposed to serve the main site. Remove an accidental sub.example.com from its server_name line and check for broad wildcards such as *.example.com that intentionally or unintentionally catch the subdomain.

Nginx evaluates exact, wildcard, and regular-expression names according to its server-name matching rules. An exact name is the clearest choice for a single subdomain. Also check whether another block is marked default_server on port 80; that block will handle names for which no better match exists.

Enable the configuration and check for duplicate definitions

On systems that use a sites-available/sites-enabled layout, place the file in the distribution’s expected directory and enable it with the platform’s normal symlink or management command. Make sure the file is actually included by the top-level Nginx configuration. A perfectly written file has no effect if it is outside the active include path.

Search the loaded configuration for the hostname and confirm that it appears in the intended block, not in two competing blocks. Duplicate exact names make the result dependent on configuration order and can be especially confusing after a migration.

Add the HTTPS server block separately

HTTP and HTTPS are separate listeners. Create a matching TLS block on port 443 rather than assuming the port-80 block will be reused:

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server {
    listen 443 ssl;
    server_name sub.example.com;

    ssl_certificate     /etc/letsencrypt/live/sub.example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/sub.example.com/privkey.pem;

    root /var/www/sub.example.com;
    index index.html;
}

Use the certificate and key paths supplied by your certificate-management system. If TLS is terminated by a load balancer or hosting platform, configure the hostname and certificate there, then ensure the request is forwarded to the correct backend block.

Validate and reload Nginx

1. Run nginx -t. Do not reload if the syntax test reports an error.
2. Fix missing semicolons, invalid paths, duplicate listen options, or certificate-file errors reported by the test.
3. Reload Nginx with the service manager used by your operating system, such as systemctl reload nginx.
4. Repeat the test from the client side using an explicit hostname and, when necessary, an explicit destination IP.

3. Fix Apache virtual-host matching

Create an explicit port-80 virtual host

Define a separate virtual host with an exact ServerName. Keep ServerAlias limited to names that should serve the same application.

<VirtualHost *:80>
    ServerName sub.example.com
    DocumentRoot /var/www/sub.example.com

    ErrorLog ${APACHE_LOG_DIR}/sub-error.log
    CustomLog ${APACHE_LOG_DIR}/sub-access.log combined
</VirtualHost>

For a proxied application, use the proxy directives required by the application and ensure the upstream target is the subdomain’s service. A static DocumentRoot does not automatically apply to a proxied site, and a proxy rule inherited from the main site can send traffic to the wrong application.

Audit ServerAlias and vhost order

Remove the subdomain from the main site’s ServerAlias list unless both names are deliberately one site. Check wildcard aliases such as *.example.com for the same reason.

Apache selects a name-based virtual host using the address and port, then the requested hostname. If no configured name matches, the first listed virtual host for that address and port is used. Therefore, an unmatched subdomain can display the main site even when Apache is running normally.

Configure a parallel 443 virtual host

HTTPS needs its own virtual host and certificate configuration:

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<VirtualHost *:443>
    ServerName sub.example.com
    DocumentRoot /var/www/sub.example.com

    SSLEngine on
    SSLCertificateFile /etc/letsencrypt/live/sub.example.com/fullchain.pem
    SSLCertificateKeyFile /etc/letsencrypt/live/sub.example.com/privkey.pem

    ErrorLog ${APACHE_LOG_DIR}/sub-ssl-error.log
    CustomLog ${APACHE_LOG_DIR}/sub-ssl-access.log combined
</VirtualHost>

The exact TLS directives and certificate paths vary by operating system and Apache modules. The hostname, content root or proxy target, and certificate coverage must all belong to the subdomain.

Enable, inspect, and reload Apache

1. On distributions that provide site-available/site-enabled tooling, enable the new site using that distribution’s standard command.
2. Run apachectl -S to display the parsed addresses, ports, virtual-host order, and duplicate names. On Windows, use httpd.exe -S.
3. Check the output for the expected ServerName on both 80 and 443, and look for a different file claiming the same hostname.
4. Run Apache’s syntax check, commonly apachectl configtest, and correct any error before reloading.
5. Reload Apache with the service manager used by your system.

4. Treat HTTPS as a separate selection problem

With HTTPS, the server may choose a virtual server during the TLS handshake from the SNI name before it can read the encrypted HTTP Host header. A correct port-80 configuration therefore does not prove that port 443 is correct.

Check all of the following for the subdomain:

• The certificate’s subject or Subject Alternative Name includes sub.example.com.
• The 443 Nginx server_name or Apache ServerName is an exact match or an intentional wildcard.
• The TLS block serves the subdomain’s document root or proxy target, not the main site’s.
• The certificate presented for the tested IP is the expected one. A certificate for the root domain often indicates that the default TLS virtual host answered.
• If a CDN, load balancer, or reverse proxy terminates TLS, its hostname-to-backend mapping is correct; changing only the origin server may not change the result seen by browsers.

5. Distinguish a wrong virtual host from an application redirect

There are two different symptoms: the server can return the main site immediately, or it can return the subdomain’s application and then redirect the browser to the root domain.

Inspect the response without following redirects:

curl -I --resolve sub.example.com:80:SERVER_IP http://sub.example.com/
curl -I --resolve sub.example.com:443:SERVER_IP https://sub.example.com/

Replace SERVER_IP with the intended IPv4 address. Use an IPv6 test if the site is published through AAAA. The --resolve option makes the request use the chosen address while retaining the hostname for the HTTP Host header and, for HTTPS, SNI.

Interpret the result as follows:

• A response containing the main site’s headers or content with no redirect usually indicates virtual-host selection, a wrong document root, or an upstream mapping error.
• A 301 or 302 with a Location: https://example.com/... header proves that some layer is issuing a redirect. Inspect application canonical-URL settings, framework base-URL variables, rewrite rules, and reverse-proxy headers.
• A redirect only when the request arrives through a proxy can indicate missing or incorrect X-Forwarded-Host or X-Forwarded-Proto handling.
• A redirect that occurs only on HTTPS can come from the TLS vhost, an HTTPS-specific rewrite, or an application that believes its public hostname is the root domain.

Review access and error logs at the same time as the curl request. The selected virtual host’s log file should record the request. If it appears in the main site’s log, the request is still being caught by the wrong configuration.

6. Test with the same hostname users send

Testing an IP address in a browser is misleading: the browser then sends the IP as the hostname, so the server is expected to choose a default site. Always test with the subdomain name and force the destination address when you need to bypass DNS.

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1. Test port 80 with curl -I --resolve sub.example.com:80:SERVER_IP http://sub.example.com/.
2. Test port 443 with curl -I --resolve sub.example.com:443:SERVER_IP https://sub.example.com/.
3. Record the status code, every Location header, the certificate subject/SAN for HTTPS, and identifying response headers.
4. Compare those results with equivalent requests for example.com. The two names may share an address but should resolve to their intended roots or upstream services.
5. After any DNS change, test from more than one network because recursive resolvers can retain cached answers until the record’s TTL expires.

Nginx and Apache: the relevant differences

Common mistakes that keep the main site appearing

The hostname is misspelled

sub.example.com, sub.example.net, and www.sub.example.com are different names. Put every deliberately supported name in the correct alias list and do not assume one spelling matches another.

The subdomain exists only on port 80

Browsers, HSTS policies, and application redirects can move users to HTTPS. A working HTTP block cannot answer for a missing or incorrect 443 block.

A wildcard catches the request first

Wildcards are useful for multi-tenant designs, but they can hide a missing exact host. Decide whether the subdomain belongs to the wildcard application or needs an exact exception, then configure the matching rules accordingly.

The file was created but never loaded

Distribution layouts, container images, and control panels use different include paths. Confirm the active configuration, not just the file on disk, contains the new block.

IPv6 reaches a different server

Some clients prefer AAAA over A. If IPv6 points to an old host whose default vhost is the main site, IPv4 tests may look correct while many users still see the wrong page.

The upstream application canonicalizes the root domain

When the web server logs show the subdomain block but the response contains a root-domain Location, update the application’s public URL and trusted-proxy settings. The web-server host match is then working; the redirect source is higher in the stack.

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Final verification checklist

• The subdomain’s A, AAAA, or CNAME records reach the intended endpoint.
• The main-domain configuration does not accidentally include the subdomain as an alias.
• Nginx has an exact server_name, or Apache has an exact ServerName, for every required port.
• The subdomain points to the correct static directory or upstream service.
• HTTPS has its own matching host configuration and a certificate covering the subdomain.
• Configuration syntax checks pass before reload.
• Apache’s parsed-vhost output or the active Nginx configuration confirms the expected block is loaded.
• Explicit curl --resolve tests show the intended status, headers, certificate, and absence of an unwanted root-domain redirect.
• Logs identify the subdomain’s virtual host and do not show the request being handled by the main site.

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