Add pid-file flag to agent

command/agent/agent.go

@@ -107,6 +107,8 @@ func Create(config *Config, logOutput io.Writer) (*Agent, error) {
 		return nil, err
 	}
 
+	agent.storePid()
+
 	return agent, nil
 }
 
@@ -250,6 +252,8 @@ func (a *Agent) Shutdown() error {
 		err = a.client.Shutdown()
 	}
 
+	a.deletePid()
+
 	a.logger.Println("[INFO] agent: shutdown complete")
 	a.shutdown = true
 	close(a.shutdownCh)
@@ -496,3 +500,36 @@ func (a *Agent) Stats() map[string]map[string]string {
 	}
 	return stats
 }
+
+func (a *Agent) storePid() {
+	pidPath := a.config.PidFile
+
+	if pidPath != "" {
+		pid := os.Getpid()
+		pidFile, err := os.OpenFile(pidPath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0666)
+
+		if err != nil {
+			fmt.Errorf("Could not open pid file: %v", err)
+		}
+
+		defer pidFile.Close()
+
+		_, err = pidFile.WriteString(fmt.Sprintf("%d", pid))
+
+		if err != nil {
+			fmt.Errorf("Could not write to pid file: %s", err)
+		}
+	}
+}
+
+func (a *Agent) deletePid() {
+	pidPath := a.config.PidFile
+
+	if pidPath != "" {
+		err := os.Remove(pidPath)
+
+		if err != nil {
+			fmt.Errorf("Could not remove pid file: %s", err)
+		}
+	}
+}

command/agent/command.go

@@ -50,6 +50,7 @@ func (c *Command) readConfig() *Config {
 	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.BoolVar(&cmdConfig.Server, "server", false, "run agent as server")
 	cmdFlags.BoolVar(&cmdConfig.Bootstrap, "bootstrap", false, "enable server bootstrap mode")
@@ -485,6 +486,7 @@ Options:
   -protocol=N              Sets the protocol version. Defaults to latest.
   -server                  Switches agent to server mode.
   -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)

command/agent/config.go

@@ -128,6 +128,9 @@ type Config struct {
 	// If provided, the UI endpoints will be enabled.
 	UiDir string `mapstructure:"ui_dir"`
 
+	// PidFile is the file to store our PID in
+	PidFile string `mapstructure:"pid_file"`
+
 	// 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.
@@ -423,6 +426,9 @@ func MergeConfig(a, b *Config) *Config {
 	if b.UiDir != "" {
 		result.UiDir = b.UiDir
 	}
+	if b.PidFile != "" {
+		result.PidFile = b.PidFile
+	}
 
 	// Copy the start join addresses
 	result.StartJoin = make([]string, 0, len(a.StartJoin)+len(b.StartJoin))

command/agent/config_test.go

@@ -257,6 +257,17 @@ func TestDecodeConfig(t *testing.T) {
 	if config.UiDir != "/opt/consul-ui" {
 		t.Fatalf("bad: %#v", config)
 	}
+
+	// Pid File
+	input = `{"pid_file": "/tmp/consul/pid"}`
+	config, err = DecodeConfig(bytes.NewReader([]byte(input)))
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if config.PidFile != "/tmp/consul/pid" {
+		t.Fatalf("bad: %#v", config)
+	}
 }
 
 func TestDecodeConfig_Service(t *testing.T) {

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

@@ -96,6 +96,9 @@ The options below are all specified on the command-line.
 * `-ui-dir` - This flag provides a the directory containing the Web UI resources
   for Consul. This must be provided to enable the Web UI. Directory must be readable.
 
+* `-pid-file` - This flag provides the file path for the agent to store it's PID. This is useful for
+  sending signals to the agent, such as `SIGINT` to close it or `SIGHUP` to update check definitions.
+
 ## Configuration Files
 
 In addition to the command-line options, configuration can be put into