read arguments in main function.

main.go

a := kingpin.New(filepath.Base(os.Args[0]), "The Prometheus monitoring server")

a.Version(version.Print("prometheus"))

a.HelpFlag.Short('h')

a.Flag("config.file", "Prometheus configuration file path.").
	Default("prometheus.yml").StringVar(&cfg.configFile)

a.Flag("web.listen-address", "Address to listen on for UI, API, and telemetry.").
	Default("0.0.0.0:9090").StringVar(&cfg.web.ListenAddress)

a.Flag("web.read-timeout",
	"Maximum duration before timing out read of the request, and closing idle connections.").
	Default("5m").SetValue(&cfg.webTimeout)

a.Flag("web.max-connections", "Maximum number of simultaneous connections.").
	Default("512").IntVar(&cfg.web.MaxConnections)

a.Flag("web.external-url",
	"The URL under which Prometheus is externally reachable (for example, if Prometheus is served via a reverse proxy). Used for generating relative and absolute links back to Prometheus itself. If the URL has a path portion, it will be used to prefix all HTTP endpoints served by Prometheus. If omitted, relevant URL components will be derived automatically.").
	PlaceHolder("<URL>").StringVar(&cfg.prometheusURL)

a.Flag("web.route-prefix",
	"Prefix for the internal routes of web endpoints. Defaults to path of --web.external-url.").
	PlaceHolder("<path>").StringVar(&cfg.web.RoutePrefix)

a.Flag("web.user-assets", "Path to static asset directory, available at /user.").
	PlaceHolder("<path>").StringVar(&cfg.web.UserAssetsPath)

a.Flag("web.enable-lifecycle", "Enable shutdown and reload via HTTP request.").
	Default("false").BoolVar(&cfg.web.EnableLifecycle)

a.Flag("web.enable-admin-api", "Enables API endpoints for admin control actions.").
	Default("false").BoolVar(&cfg.web.EnableAdminAPI)

a.Flag("web.console.templates", "Path to the console template directory, available at /consoles.").
	Default("consoles").StringVar(&cfg.web.ConsoleTemplatesPath)

a.Flag("web.console.libraries", "Path to the console library directory.").
	Default("console_libraries").StringVar(&cfg.web.ConsoleLibrariesPath)

a.Flag("storage.tsdb.path", "Base path for metrics storage.").
	Default("data/").StringVar(&cfg.localStoragePath)

a.Flag("storage.tsdb.min-block-duration", "Minimum duration of a data block before being persisted. For use in testing.").
	Hidden().Default("2h").SetValue(&cfg.tsdb.MinBlockDuration)

a.Flag("storage.tsdb.max-block-duration",
	"Maximum duration compacted blocks may span. For use in testing. (Defaults to 10% of the retention period).").
	Hidden().PlaceHolder("<duration>").SetValue(&cfg.tsdb.MaxBlockDuration)

a.Flag("storage.tsdb.retention", "How long to retain samples in the storage.").
	Default("15d").SetValue(&cfg.tsdb.Retention)

a.Flag("storage.tsdb.no-lockfile", "Do not create lockfile in data directory.").
	Default("false").BoolVar(&cfg.tsdb.NoLockfile)

a.Flag("alertmanager.notification-queue-capacity", "The capacity of the queue for pending alert manager notifications.").
	Default("10000").IntVar(&cfg.notifier.QueueCapacity)

a.Flag("alertmanager.timeout", "Timeout for sending alerts to Alertmanager.").
	Default("10s").SetValue(&cfg.notifierTimeout)

a.Flag("query.lookback-delta", "The delta difference allowed for retrieving metrics during expression evaluations.").
	Default("5m").SetValue(&cfg.lookbackDelta)

a.Flag("query.timeout", "Maximum time a query may take before being aborted.").
	Default("2m").SetValue(&cfg.queryTimeout)

a.Flag("query.max-concurrency", "Maximum number of queries executed concurrently.").
	Default("20").IntVar(&cfg.queryConcurrency)