public VirtualHostBuilder virtualHost(String hostnamePattern) {
        final VirtualHostBuilder virtualHostBuilder = findOrCreateVirtualHostBuilder(hostnamePattern);
        virtualHostBuilders.add(virtualHostBuilder);
        return virtualHostBuilder;
    }
Adds the <a href="https://en.wikipedia.org/wiki/Virtual_hosting#Name-based">name-based virtual host</a>.

@param hostnamePattern virtual host name regular expression
@return {@link VirtualHostBuilder} for building the virtual host
core/src/main/java/com/linecorp/armeria/server/ServerBuilder.java