void setServerConfig(ServerConfig serverConfig) {
        if (this.serverConfig != null) {
            throw new IllegalStateException("VirtualHost cannot be added to more than one Server.");
        }

        this.serverConfig = requireNonNull(serverConfig, "serverConfig");

        final MeterRegistry registry = serverConfig.meterRegistry();
        final MeterIdPrefix idPrefix =
                new MeterIdPrefix("armeria.server.router.virtual.host.cache",
                                  "hostname.pattern", hostnamePattern);
        router.registerMetrics(registry, idPrefix);
    }
Returns the {@link Server} where this {@link VirtualHost} belongs to.
core/src/main/java/com/linecorp/armeria/server/VirtualHost.java