command.go

package agent

import (
	"flag"
	"fmt"
	"io"
	"net"
	"os"
	"os/signal"
	"path/filepath"
	"regexp"
	"runtime"
	"strings"
	"syscall"
	"time"

	"github.com/armon/go-metrics"
	"github.com/hashicorp/consul/watch"
	"github.com/hashicorp/go-checkpoint"
	"github.com/hashicorp/go-syslog"
	"github.com/hashicorp/logutils"
	"github.com/mitchellh/cli"
)

// gracefulTimeout controls how long we wait before forcefully terminating
var gracefulTimeout = 5 * time.Second

// validDatacenter is used to validate a datacenter
var validDatacenter = regexp.MustCompile("^[a-zA-Z0-9_-]+$")

// Command is a Command implementation that runs a Consul agent.
// The command will not end unless a shutdown message is sent on the
// ShutdownCh. If two messages are sent on the ShutdownCh it will forcibly
// exit.
type Command struct {
	Revision          string
	Version           string
	VersionPrerelease string
	Ui                cli.Ui
	ShutdownCh        <-chan struct{}
	args              []string
	logFilter         *logutils.LevelFilter
	logOutput         io.Writer
	agent             *Agent
	rpcServer         *AgentRPC
	httpServer        *HTTPServer
	dnsServer         *DNSServer
}

// readConfig is responsible for setup of our configuration using
// the command line and any file configs
func (c *Command) readConfig() *Config {
	var cmdConfig Config
	var configFiles []string
	var retryInterval string
	cmdFlags := flag.NewFlagSet("agent", flag.ContinueOnError)
	cmdFlags.Usage = func() { c.Ui.Output(c.Help()) }

	cmdFlags.Var((*AppendSliceValue)(&configFiles), "config-file", "json file to read config from")
	cmdFlags.Var((*AppendSliceValue)(&configFiles), "config-dir", "directory of json files to read")

	cmdFlags.StringVar(&cmdConfig.LogLevel, "log-level", "", "log level")
	cmdFlags.StringVar(&cmdConfig.NodeName, "node", "", "node name")
	cmdFlags.StringVar(&cmdConfig.Datacenter, "dc", "", "node datacenter")
	cmdFlags.StringVar(&cmdConfig.DataDir, "data-dir", "", "path to the data directory")
	cmdFlags.StringVar(&cmdConfig.UiDir, "ui-dir", "", "path to the web UI directory")
	cmdFlags.StringVar(&cmdConfig.PidFile, "pid-file", "", "path to file to store PID")
	cmdFlags.StringVar(&cmdConfig.EncryptKey, "encrypt", "", "gossip encryption key")

	cmdFlags.BoolVar(&cmdConfig.Server, "server", false, "run agent as server")
	cmdFlags.BoolVar(&cmdConfig.Bootstrap, "bootstrap", false, "enable server bootstrap mode")
	cmdFlags.IntVar(&cmdConfig.BootstrapExpect, "bootstrap-expect", 0, "enable automatic bootstrap via expect mode")

	cmdFlags.StringVar(&cmdConfig.ClientAddr, "client", "", "address to bind client listeners to (DNS, HTTP, RPC)")
	cmdFlags.StringVar(&cmdConfig.BindAddr, "bind", "", "address to bind server listeners to")
	cmdFlags.StringVar(&cmdConfig.AdvertiseAddr, "advertise", "", "address to advertise instead of bind addr")

	cmdFlags.IntVar(&cmdConfig.Protocol, "protocol", -1, "protocol version")

	cmdFlags.BoolVar(&cmdConfig.EnableSyslog, "syslog", false,
		"enable logging to syslog facility")
	cmdFlags.BoolVar(&cmdConfig.RejoinAfterLeave, "rejoin", false,
		"enable re-joining after a previous leave")
	cmdFlags.Var((*AppendSliceValue)(&cmdConfig.StartJoin), "join",
		"address of agent to join on startup")
	cmdFlags.Var((*AppendSliceValue)(&cmdConfig.RetryJoin), "retry-join",
		"address of agent to join on startup with retry")
	cmdFlags.IntVar(&cmdConfig.RetryMaxAttempts, "retry-max", 0,
		"number of retries for joining")
	cmdFlags.StringVar(&retryInterval, "retry-interval", "",
		"interval between join attempts")

	if err := cmdFlags.Parse(c.args); err != nil {
		return nil
	}

	if retryInterval != "" {
		dur, err := time.ParseDuration(retryInterval)
		if err != nil {
			c.Ui.Error(fmt.Sprintf("Error: %s", err))
			return nil
		}
		cmdConfig.RetryInterval = dur
	}

	config := DefaultConfig()
	if len(configFiles) > 0 {
		fileConfig, err := ReadConfigPaths(configFiles)
		if err != nil {
			c.Ui.Error(err.Error())
			return nil
		}

		config = MergeConfig(config, fileConfig)
	}

	config = MergeConfig(config, &cmdConfig)

	if config.NodeName == "" {
		hostname, err := os.Hostname()
		if err != nil {
			c.Ui.Error(fmt.Sprintf("Error determining hostname: %s", err))
			return nil
		}
		config.NodeName = hostname
	}

	if config.EncryptKey != "" {
		if _, err := config.EncryptBytes(); err != nil {
			c.Ui.Error(fmt.Sprintf("Invalid encryption key: %s", err))
			return nil
		}
	}

	// Ensure we have a data directory
	if config.DataDir == "" {
		c.Ui.Error("Must specify data directory using -data-dir")
		return nil
	}

	// Verify data center is valid
	if !validDatacenter.MatchString(config.Datacenter) {
		c.Ui.Error("Datacenter must be alpha-numeric with underscores and hypens only")
		return nil
	}

	// Only allow bootstrap mode when acting as a server
	if config.Bootstrap && !config.Server {
		c.Ui.Error("Bootstrap mode cannot be enabled when server mode is not enabled")
		return nil
	}

	// Expect can only work when acting as a server
	if config.BootstrapExpect != 0 && !config.Server {
		c.Ui.Error("Expect mode cannot be enabled when server mode is not enabled")
		return nil
	}

	// Expect & Bootstrap are mutually exclusive
	if config.BootstrapExpect != 0 && config.Bootstrap {
		c.Ui.Error("Bootstrap cannot be provided with an expected server count")
		return nil
	}

	// Compile all the watches
	for _, params := range config.Watches {
		// Parse the watches, excluding the handler
		wp, err := watch.ParseExempt(params, []string{"handler"})
		if err != nil {
			c.Ui.Error(fmt.Sprintf("Failed to parse watch (%#v): %v", params, err))
			return nil
		}

		// Get the handler
		if err := verifyWatchHandler(wp.Exempt["handler"]); err != nil {
			c.Ui.Error(fmt.Sprintf("Failed to setup watch handler (%#v): %v", params, err))
			return nil
		}

		// Store the watch plan
		config.WatchPlans = append(config.WatchPlans, wp)
	}

	// Warn if we are in expect mode
	if config.BootstrapExpect == 1 {
		c.Ui.Error("WARNING: BootstrapExpect Mode is specified as 1; this is the same as Bootstrap mode.")
		config.BootstrapExpect = 0
		config.Bootstrap = true
	} else if config.BootstrapExpect > 0 {
		c.Ui.Error(fmt.Sprintf("WARNING: Expect Mode enabled, expecting %d servers", config.BootstrapExpect))
	}

	// Warn if we are in bootstrap mode
	if config.Bootstrap {
		c.Ui.Error("WARNING: Bootstrap mode enabled! Do not enable unless necessary")
	}

	// Warn if using windows as a server
	if config.Server && runtime.GOOS == "windows" {
		c.Ui.Error("WARNING: Windows is not recommended as a Consul server. Do not use in production.")
	}

	// Set the version info
	config.Revision = c.Revision
	config.Version = c.Version
	config.VersionPrerelease = c.VersionPrerelease

	return config
}

// setupLoggers is used to setup the logGate, logWriter, and our logOutput
func (c *Command) setupLoggers(config *Config) (*GatedWriter, *logWriter, io.Writer) {
	// Setup logging. First create the gated log writer, which will
	// store logs until we're ready to show them. Then create the level
	// filter, filtering logs of the specified level.
	logGate := &GatedWriter{
		Writer: &cli.UiWriter{Ui: c.Ui},
	}

	c.logFilter = LevelFilter()
	c.logFilter.MinLevel = logutils.LogLevel(strings.ToUpper(config.LogLevel))
	c.logFilter.Writer = logGate
	if !ValidateLevelFilter(c.logFilter.MinLevel, c.logFilter) {
		c.Ui.Error(fmt.Sprintf(
			"Invalid log level: %s. Valid log levels are: %v",
			c.logFilter.MinLevel, c.logFilter.Levels))
		return nil, nil, nil
	}

	// Check if syslog is enabled
	var syslog io.Writer
	if config.EnableSyslog {
		l, err := gsyslog.NewLogger(gsyslog.LOG_NOTICE, config.SyslogFacility, "consul")
		if err != nil {
			c.Ui.Error(fmt.Sprintf("Syslog setup failed: %v", err))
			return nil, nil, nil
		}
		syslog = &SyslogWrapper{l, c.logFilter}
	}

	// Create a log writer, and wrap a logOutput around it
	logWriter := NewLogWriter(512)
	var logOutput io.Writer
	if syslog != nil {
		logOutput = io.MultiWriter(c.logFilter, logWriter, syslog)
	} else {
		logOutput = io.MultiWriter(c.logFilter, logWriter)
	}
	c.logOutput = logOutput
	return logGate, logWriter, logOutput
}

// setupAgent is used to start the agent and various interfaces
func (c *Command) setupAgent(config *Config, logOutput io.Writer, logWriter *logWriter) error {
	c.Ui.Output("Starting Consul agent...")
	agent, err := Create(config, logOutput)
	if err != nil {
		c.Ui.Error(fmt.Sprintf("Error starting agent: %s", err))
		return err
	}
	c.agent = agent

	// Setup the RPC listener
	rpcAddr, err := config.ClientListener(config.Addresses.RPC, config.Ports.RPC)
	if err != nil {
		c.Ui.Error(fmt.Sprintf("Invalid RPC bind address: %s", err))
		return err
	}

	rpcListener, err := net.Listen("tcp", rpcAddr.String())
	if err != nil {
		agent.Shutdown()
		c.Ui.Error(fmt.Sprintf("Error starting RPC listener: %s", err))
		return err
	}

	// Start the IPC layer
	c.Ui.Output("Starting Consul agent RPC...")
	c.rpcServer = NewAgentRPC(agent, rpcListener, logOutput, logWriter)

	if config.Ports.HTTP > 0 {
		httpAddr, err := config.ClientListener(config.Addresses.HTTP, config.Ports.HTTP)
		if err != nil {
			c.Ui.Error(fmt.Sprintf("Invalid HTTP bind address: %s", err))
			return err
		}

		server, err := NewHTTPServer(agent, config.UiDir, config.EnableDebug, logOutput, httpAddr.String())
		if err != nil {
			agent.Shutdown()
			c.Ui.Error(fmt.Sprintf("Error starting http server: %s", err))
			return err
		}
		c.httpServer = server
	}

	if config.Ports.DNS > 0 {
		dnsAddr, err := config.ClientListener(config.Addresses.DNS, config.Ports.DNS)
		if err != nil {
			c.Ui.Error(fmt.Sprintf("Invalid DNS bind address: %s", err))
			return err
		}

		server, err := NewDNSServer(agent, &config.DNSConfig, logOutput,
			config.Domain, dnsAddr.String(), config.DNSRecursor)
		if err != nil {
			agent.Shutdown()
			c.Ui.Error(fmt.Sprintf("Error starting dns server: %s", err))
			return err
		}
		c.dnsServer = server
	}

	// Setup update checking
	if !config.DisableUpdateCheck {
		updateParams := &checkpoint.CheckParams{
			Product: "consul",
			Version: fmt.Sprintf("%s%s", config.Version, config.VersionPrerelease),
		}
		if !config.DisableAnonymousSignature {
			updateParams.SignatureFile = filepath.Join(config.DataDir, "checkpoint-signature")
		}

		// Schedule a periodic check with expected interval of 24 hours
		checkpoint.CheckInterval(updateParams, 24*time.Hour, c.checkpointResults)

		// Do an immediate check within the next 30 seconds
		go func() {
			time.Sleep(randomStagger(30 * time.Second))
			c.checkpointResults(checkpoint.Check(updateParams))
		}()
	}

	return nil
}

// checkpointResults is used to handler periodic results from our update checker
func (c *Command) checkpointResults(results *checkpoint.CheckResponse, err error) {
	if err != nil {
		c.Ui.Error(fmt.Sprintf("Failed to check for updates: %v", err))
		return
	}
	if results.Outdated {
		c.Ui.Error(fmt.Sprintf("Newer Consul version available: %s", results.CurrentVersion))
	}
	for _, alert := range results.Alerts {
		switch alert.Level {
		case "info":
			c.Ui.Info(fmt.Sprintf("Bulletin [%s]: %s (%s)", alert.Level, alert.Message, alert.URL))
		default:
			c.Ui.Error(fmt.Sprintf("Bulletin [%s]: %s (%s)", alert.Level, alert.Message, alert.URL))
		}
	}
}

// startupJoin is invoked to handle any joins specified to take place at start time
func (c *Command) startupJoin(config *Config) error {
	if len(config.StartJoin) == 0 {
		return nil
	}

	c.Ui.Output("Joining cluster...")
	n, err := c.agent.JoinLAN(config.StartJoin)
	if err != nil {
		return err
	}

	c.Ui.Info(fmt.Sprintf("Join completed. Synced with %d initial agents", n))
	return nil
}

// retryJoin is used to handle retrying a join until it succeeds or all
// retries are exhausted.
func (c *Command) retryJoin(config *Config, errCh chan<- struct{}) {
	if len(config.RetryJoin) == 0 {
		return
	}

	logger := c.agent.logger
	logger.Printf("[INFO] agent: Joining cluster...")

	attempt := 0
	for {
		n, err := c.agent.JoinLAN(config.RetryJoin)
		if err == nil {
			logger.Printf("[INFO] agent: Join completed. Synced with %d initial agents", n)
			return
		}

		attempt++
		if config.RetryMaxAttempts > 0 && attempt > config.RetryMaxAttempts {
			logger.Printf("[ERROR] agent: max join retry exhausted, exiting")
			close(errCh)
			return
		}

		logger.Printf("[WARN] agent: Join failed: %v, retrying in %v", err,
			config.RetryInterval)
		time.Sleep(config.RetryInterval)
	}
}

func (c *Command) Run(args []string) int {
	c.Ui = &cli.PrefixedUi{
		OutputPrefix: "==> ",
		InfoPrefix:   "    ",
		ErrorPrefix:  "==> ",
		Ui:           c.Ui,
	}

	// Parse our configs
	c.args = args
	config := c.readConfig()
	if config == nil {
		return 1
	}

	// Check GOMAXPROCS
	if runtime.GOMAXPROCS(0) == 1 {
		c.Ui.Error("WARNING: It is highly recommended to set GOMAXPROCS higher than 1")
	}

	// Setup the log outputs
	logGate, logWriter, logOutput := c.setupLoggers(config)
	if logWriter == nil {
		return 1
	}

	/* Setup telemetry
	Aggregate on 10 second intervals for 1 minute. Expose the
	metrics over stderr when there is a SIGUSR1 received.
	*/
	inm := metrics.NewInmemSink(10*time.Second, time.Minute)
	metrics.DefaultInmemSignal(inm)
	metricsConf := metrics.DefaultConfig("consul")

	// Configure the statsite sink
	var fanout metrics.FanoutSink
	if config.StatsiteAddr != "" {
		sink, err := metrics.NewStatsiteSink(config.StatsiteAddr)
		if err != nil {
			c.Ui.Error(fmt.Sprintf("Failed to start statsite sink. Got: %s", err))
			return 1
		}
		fanout = append(fanout, sink)
	}

	// Configure the statsd sink
	if config.StatsdAddr != "" {
		sink, err := metrics.NewStatsdSink(config.StatsdAddr)
		if err != nil {
			c.Ui.Error(fmt.Sprintf("Failed to start statsd sink. Got: %s", err))
			return 1
		}
		fanout = append(fanout, sink)
	}

	// Initialize the global sink
	if len(fanout) > 0 {
		fanout = append(fanout, inm)
		metrics.NewGlobal(metricsConf, fanout)
	} else {
		metricsConf.EnableHostname = false
		metrics.NewGlobal(metricsConf, inm)
	}

	// Create the agent
	if err := c.setupAgent(config, logOutput, logWriter); err != nil {
		return 1
	}
	defer c.agent.Shutdown()
	if c.rpcServer != nil {
		defer c.rpcServer.Shutdown()
	}
	if c.httpServer != nil {
		defer c.httpServer.Shutdown()
	}

	// Join startup nodes if specified
	if err := c.startupJoin(config); err != nil {
		c.Ui.Error(err.Error())
		return 1
	}

	// Register the services
	for _, service := range config.Services {
		ns := service.NodeService()
		chkType := service.CheckType()
		if err := c.agent.AddService(ns, chkType); err != nil {
			c.Ui.Error(fmt.Sprintf("Failed to register service '%s': %v", service.Name, err))
			return 1
		}
	}

	// Register the checks
	for _, check := range config.Checks {
		health := check.HealthCheck(config.NodeName)
		chkType := &check.CheckType
		if err := c.agent.AddCheck(health, chkType); err != nil {
			c.Ui.Error(fmt.Sprintf("Failed to register check '%s': %v %v", check.Name, err, check))
			return 1
		}
	}

	// Get the new client listener addr
	httpAddr, err := config.ClientListenerAddr(config.Addresses.HTTP, config.Ports.HTTP)
	if err != nil {
		c.Ui.Error(fmt.Sprintf("Failed to determine HTTP address: %v", err))
	}

	// Register the watches
	for _, wp := range config.WatchPlans {
		go func(wp *watch.WatchPlan) {
			wp.Handler = makeWatchHandler(logOutput, wp.Exempt["handler"])
			wp.LogOutput = c.logOutput
			if err := wp.Run(httpAddr); err != nil {
				c.Ui.Error(fmt.Sprintf("Error running watch: %v", err))
			}
		}(wp)
	}

	// Let the agent know we've finished registration
	c.agent.StartSync()

	c.Ui.Output("Consul agent running!")
	c.Ui.Info(fmt.Sprintf("     Node name: '%s'", config.NodeName))
	c.Ui.Info(fmt.Sprintf("    Datacenter: '%s'", config.Datacenter))
	c.Ui.Info(fmt.Sprintf("        Server: %v (bootstrap: %v)", config.Server, config.Bootstrap))
	c.Ui.Info(fmt.Sprintf("   Client Addr: %v (HTTP: %d, DNS: %d, RPC: %d)", config.ClientAddr,
		config.Ports.HTTP, config.Ports.DNS, config.Ports.RPC))
	c.Ui.Info(fmt.Sprintf("  Cluster Addr: %v (LAN: %d, WAN: %d)", config.AdvertiseAddr,
		config.Ports.SerfLan, config.Ports.SerfWan))
	c.Ui.Info(fmt.Sprintf("Gossip encrypt: %v, RPC-TLS: %v, TLS-Incoming: %v",
		config.EncryptKey != "", config.VerifyOutgoing, config.VerifyIncoming))

	// Enable log streaming
	c.Ui.Info("")
	c.Ui.Output("Log data will now stream in as it occurs:\n")
	logGate.Flush()

	// Start retry join process
	errCh := make(chan struct{})
	go c.retryJoin(config, errCh)

	// Wait for exit
	return c.handleSignals(config, errCh)
}

// handleSignals blocks until we get an exit-causing signal
func (c *Command) handleSignals(config *Config, retryJoin <-chan struct{}) int {
	signalCh := make(chan os.Signal, 4)
	signal.Notify(signalCh, os.Interrupt, syscall.SIGTERM, syscall.SIGHUP)

	// Wait for a signal
WAIT:
	var sig os.Signal
	select {
	case s := <-signalCh:
		sig = s
	case <-c.rpcServer.ReloadCh():
		sig = syscall.SIGHUP
	case <-c.ShutdownCh:
		sig = os.Interrupt
	case <-retryJoin:
		return 1
	case <-c.agent.ShutdownCh():
		// Agent is already shutdown!
		return 0
	}
	c.Ui.Output(fmt.Sprintf("Caught signal: %v", sig))

	// Check if this is a SIGHUP
	if sig == syscall.SIGHUP {
		config = c.handleReload(config)
		goto WAIT
	}

	// Check if we should do a graceful leave
	graceful := false
	if sig == os.Interrupt && !config.SkipLeaveOnInt {
		graceful = true
	} else if sig == syscall.SIGTERM && config.LeaveOnTerm {
		graceful = true
	}

	// Bail fast if not doing a graceful leave
	if !graceful {
		return 1
	}

	// Attempt a graceful leave
	gracefulCh := make(chan struct{})
	c.Ui.Output("Gracefully shutting down agent...")
	go func() {
		if err := c.agent.Leave(); err != nil {
			c.Ui.Error(fmt.Sprintf("Error: %s", err))
			return
		}
		close(gracefulCh)
	}()

	// Wait for leave or another signal
	select {
	case <-signalCh:
		return 1
	case <-time.After(gracefulTimeout):
		return 1
	case <-gracefulCh:
		return 0
	}
}

// handleReload is invoked when we should reload our configs, e.g. SIGHUP
func (c *Command) handleReload(config *Config) *Config {
	c.Ui.Output("Reloading configuration...")
	newConf := c.readConfig()
	if newConf == nil {
		c.Ui.Error(fmt.Sprintf("Failed to reload configs"))
		return config
	}

	// Change the log level
	minLevel := logutils.LogLevel(strings.ToUpper(newConf.LogLevel))
	if ValidateLevelFilter(minLevel, c.logFilter) {
		c.logFilter.SetMinLevel(minLevel)
	} else {
		c.Ui.Error(fmt.Sprintf(
			"Invalid log level: %s. Valid log levels are: %v",
			minLevel, c.logFilter.Levels))

		// Keep the current log level
		newConf.LogLevel = config.LogLevel
	}

	// Bulk update the services and checks
	c.agent.PauseSync()
	defer c.agent.ResumeSync()

	// Deregister the old services
	for _, service := range config.Services {
		ns := service.NodeService()
		c.agent.RemoveService(ns.ID)
	}

	// Deregister the old checks
	for _, check := range config.Checks {
		health := check.HealthCheck(config.NodeName)
		c.agent.RemoveCheck(health.CheckID)
	}

	// Register the services
	for _, service := range newConf.Services {
		ns := service.NodeService()
		chkType := service.CheckType()
		if err := c.agent.AddService(ns, chkType); err != nil {
			c.Ui.Error(fmt.Sprintf("Failed to register service '%s': %v", service.Name, err))
		}
	}

	// Register the checks
	for _, check := range newConf.Checks {
		health := check.HealthCheck(config.NodeName)
		chkType := &check.CheckType
		if err := c.agent.AddCheck(health, chkType); err != nil {
			c.Ui.Error(fmt.Sprintf("Failed to register check '%s': %v %v", check.Name, err, check))
		}
	}

	// Get the new client listener addr
	httpAddr, err := newConf.ClientListenerAddr(config.Addresses.HTTP, config.Ports.HTTP)
	if err != nil {
		c.Ui.Error(fmt.Sprintf("Failed to determine HTTP address: %v", err))
	}

	// Deregister the old watches
	for _, wp := range config.WatchPlans {
		wp.Stop()
	}

	// Register the new watches
	for _, wp := range newConf.WatchPlans {
		go func(wp *watch.WatchPlan) {
			wp.Handler = makeWatchHandler(c.logOutput, wp.Exempt["handler"])
			wp.LogOutput = c.logOutput
			if err := wp.Run(httpAddr); err != nil {
				c.Ui.Error(fmt.Sprintf("Error running watch: %v", err))
			}
		}(wp)
	}

	return newConf
}

func (c *Command) Synopsis() string {
	return "Runs a Consul agent"
}

func (c *Command) Help() string {
	helpText := `
Usage: consul agent [options]

  Starts the Consul agent and runs until an interrupt is received. The
  agent represents a single node in a cluster.

Options:

  -advertise=addr          Sets the advertise address to use
  -bootstrap               Sets server to bootstrap mode
  -bind=0.0.0.0            Sets the bind address for cluster communication
  -bootstrap-expect=0      Sets server to expect bootstrap mode.
  -client=127.0.0.1        Sets the address to bind for client access.
                           This includes RPC, DNS and HTTP
  -config-file=foo         Path to a JSON file to read configuration from.
                           This can be specified multiple times.
  -config-dir=foo          Path to a directory to read configuration files
                           from. This will read every file ending in ".json"
                           as configuration in this directory in alphabetical
                           order.
  -data-dir=path           Path to a data directory to store agent state
  -dc=east-aws             Datacenter of the agent
  -encrypt=key             Provides the gossip encryption key
  -join=1.2.3.4            Address of an agent to join at start time.
                           Can be specified multiple times.
  -retry-join=1.2.3.4      Address of an agent to join at start time with
                           retries enabled. Can be specified multiple times.
  -retry-interval=30s      Time to wait between join attempts.
  -retry-max=0             Maximum number of join attempts. Defaults to 0, which
                           will retry indefinitely.
  -log-level=info          Log level of the agent.
  -node=hostname           Name of this node. Must be unique in the cluster
  -protocol=N              Sets the protocol version. Defaults to latest.
  -rejoin                  Ignores a previous leave and attempts to rejoin the cluster.
  -server                  Switches agent to server mode.
  -syslog                  Enables logging to syslog
  -ui-dir=path             Path to directory containing the Web UI resources
  -pid-file=path           Path to file to store agent PID

 `
	return strings.TrimSpace(helpText)
}