Rewrite rule for subdomains

Question

Is it possible to use .htaccess for a subdomain to point to a file on the main domain? I have example.com as a main domain and created subdomains: one.example.com, two.example.c

Answer 1

A RewriteRule with a target on another server will always do a redirect

Absolute URL
If an absolute URL is specified, mod_rewrite checks to see whether the hostname matches the current host. If it does, the scheme and hostname are stripped out and the resulting path is treated as a URL-path. Otherwise, an external redirect is performed for the given URL. To force an external redirect back to the current host, see the [R] flag below.

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To map the URL http://example.com/app.php into your subdomains without redirecting, you might try the P|proxy flag

RewriteRule ^(.*)$ http://example.com/app.php/$1 [P,QSA]

Also keep the final note in mind

Note: mod_proxy must be enabled in order to use this flag.

Usually, this can be done by

a2enmod proxy proxy_http

If the target URL is https://..., you must also enable mod_proxy_connect, and activate SSL in your main or virtual host config with SSLProxyEngine

SSLProxyEngine on

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Depending on your needs, ProxyPass might be a viable solution too.