agent: Adding support for -join flag. Fixes #33.

command/agent/command.go

@@ -58,6 +58,9 @@ func (c *Command) readConfig() *Config {
 
 	cmdFlags.IntVar(&cmdConfig.Protocol, "protocol", -1, "protocol version")
 
+	cmdFlags.Var((*AppendSliceValue)(&cmdConfig.StartJoin), "join",
+		"address of agent to join on startup")
+
 	if err := cmdFlags.Parse(c.args); err != nil {
 		return nil
 	}
@@ -200,6 +203,22 @@ func (c *Command) setupAgent(config *Config, logOutput io.Writer, logWriter *log
 	return nil
 }
 
+// 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
+}
+
 func (c *Command) Run(args []string) int {
 	c.Ui = &cli.PrefixedUi{
 		OutputPrefix: "==> ",
@@ -262,6 +281,12 @@ func (c *Command) Run(args []string) int {
 		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()
@@ -447,6 +472,8 @@ Options:
                            order.
   -data-dir=path           Path to a data directory to store agent state
   -dc=east-aws             Datacenter of the agent
+  -join=1.2.3.4            Address of an agent to join at start time.
+                           Can be specified multiple times.
   -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.

command/agent/config.go

@@ -119,6 +119,11 @@ type Config struct {
 	// Must be provided to serve TLS connections.
 	KeyFile string `mapstructure:"key_file"`
 
+	// StartJoin is a list of addresses to attempt to join when the
+	// agent starts. If Serf is unable to communicate with any of these
+	// addresses, then the agent will error and exit.
+	StartJoin []string `mapstructure:"start_join"`
+
 	// AEInterval controls the anti-entropy interval. This is how often
 	// the agent attempts to reconcile it's local state with the server'
 	// representation of our state. Defaults to every 60s.
@@ -396,6 +401,12 @@ func MergeConfig(a, b *Config) *Config {
 	if b.Ports.Server != 0 {
 		result.Ports.Server = b.Ports.Server
 	}
+
+	// Copy the start join addresses
+	result.StartJoin = make([]string, 0, len(a.StartJoin)+len(b.StartJoin))
+	result.StartJoin = append(result.StartJoin, a.StartJoin...)
+	result.StartJoin = append(result.StartJoin, b.StartJoin...)
+
 	return &result
 }
 

website/source/docs/agent/options.html.markdown

@@ -66,6 +66,11 @@ The options below are all specified on the command-line.
   it relies on proper configuration. Nodes in the same datacenter should be on a single
   LAN.
 
+* `-join` - Address of another agent to join upon starting up. This can be
+  specified multiple times to specify multiple agents to join. If Consul is
+  unable to join with any of the specified addresses, agent startup will
+  fail. By default, the agent won't join any nodes when it starts up.
+
 * `-log-level` - The level of logging to show after the Consul agent has
   started. This defaults to "info". The available log levels are "trace",
   "debug", "info", "warn", "err". This is the log level that will be shown
@@ -190,6 +195,9 @@ definitions support being updated during a reload.
   gracefully leave, but setting this to true disables that. Defaults to false.
   Interrupts are usually from a Control-C from a shell.
 
+* `start_join` - An array of strings specifying addresses of nodes to
+  join upon startup.
+
 * `statsite_addr` - This provides the address of a statsite instance. If provided
   Consul will stream various telemetry information to that instance for aggregation.
   This can be used to capture various runtime information.