@Override
    public void serviceAdded(ServiceConfig cfg) throws Exception {
        final MeterRegistry registry = cfg.server().meterRegistry();
        if (cache != null) {
            final MeterIdPrefix meterIdPrefix =
                    new MeterIdPrefix("armeria.server.file.vfs.cache",
                                      "hostname.pattern",
                                      cfg.virtualHost().hostnamePattern(),
                                      "route", cfg.route().patternString(),
                                      "vfs", config.vfs().meterTag());

            CaffeineMetricSupport.setup(registry, meterIdPrefix, cache);
        }
    }
Returns a new {@link FileServiceBuilder} with the specified {@link HttpVfs}.
core/src/main/java/com/linecorp/armeria/server/file/FileService.java