Vhost

Vhost, short for virtual host, is a server configuration concept used by web servers to host multiple websites from a single physical machine. Each virtual host defines settings such as the domain name, document root, and specific logging.

In practice, the web server uses the Host header from HTTP requests to select the appropriate virtual host. For TLS, Server Name Indication (SNI) allows serving multiple SSL certificates on one IP address, enabling secure connections for multiple vhosts. DNS maps each domain to the server’s IP, while the server routes the request to the matching vhost.

There are two primary approaches: name-based virtual hosting and IP-based virtual hosting. Name-based hosting serves different hostnames over the same IP, while IP-based assigns a distinct IP per vhost. Port-based hosting is rare for HTTP but conceptually possible.

Common implementations: In Apache, virtual hosts are configured with blocks such as VirtualHost *:80 and include directives such as ServerName and DocumentRoot. In Nginx, the equivalent is a server block with listen directives and server_name, plus root and log settings. These blocks typically live in separate files and can be enabled or disabled independently.

Benefits include efficient resource use, simplified maintenance, and flexible hosting of multiple domains. Drawbacks can include certificate management for HTTPS, potential performance tuning needs, and the need for careful isolation of per-vhost resources and permissions.

See also: web server, HTTP Host header, SSL/TLS, DNS.