feat(unit.command): Add command field to units

Documentation/cloud-config.md

@@ -28,9 +28,16 @@ coreos:
 Arbitrary systemd units may be provided in the `coreos.units` attribute.
 `coreos.units` is a list of objects with the following fields:
 
-- **name**: string representing unit's name
-- **runtime**: boolean indicating whether or not to persist the unit across reboots. This is analagous to the `--runtime` flag to `systemd enable`.
-- **content**: plaintext string representing entire unit file
+- **name**: String representing unit's name. Required.
+- **runtime**: Boolean indicating whether or not to persist the unit across reboots. This is analagous to the `--runtime` argument to `systemd enable`. Default value is false.
+- **content**: Plaintext string representing entire unit file. If no value is provided, the unit is assumed to exist already.
+- **command**: Command to execute on unit: start, stop, reload, restart, try-restart, reload-or-restart, reload-or-try-restart. Default value is restart.
+
+**NOTE:** The command field is ignored for all network, netdev, and link units. The systemd-networkd.service unit will be restarted in their place.
+
+##### Examples
+
+Write a unit to disk, automatically starting it.
 
 ```
 #cloud-config
@@ -53,6 +60,19 @@ coreos:
           WantedBy=local.target
 ```
 
+Start the builtin `etcd` and `fleet` services:
+
+```
+# cloud-config
+
+coreos:
+    units:
+      - name: etcd.service
+        command: start
+      - name: fleet.service
+        command: start
+
+
 ## Cloud-Config Parameters
 
 ### ssh_authorized_keys

initialize/config.go

@@ -114,26 +114,49 @@ func Apply(cfg CloudConfig, env *Environment) error {
 	}
 
 	if len(cfg.Coreos.Units) > 0 {
+		commands := make(map[string]string, 0)
+
 		for _, unit := range cfg.Coreos.Units {
-			log.Printf("Placing unit %s on filesystem", unit.Name)
-			dst, err := system.PlaceUnit(&unit, env.Root())
+			if unit.Content != "" {
+				log.Printf("Writing unit %s to filesystem", unit.Name)
+				dst, err := system.PlaceUnit(&unit, env.Root())
+				if err != nil {
+					return err
+				}
+				log.Printf("Placed unit %s at %s", unit.Name, dst)
+
+				if unit.Group() != "network" {
+					log.Printf("Enabling unit file %s", dst)
+					if err := system.EnableUnitFile(dst, unit.Runtime); err != nil {
+						return err
+					}
+					log.Printf("Enabled unit %s", unit.Name)
+				} else {
+					log.Printf("Skipping enable for network-like unit %s", unit.Name)
+				}
+			}
+
+			if unit.Group() != "network" {
+				command := unit.Command
+				if command == "" {
+					command = "restart"
+				}
+				commands[unit.Name] = command
+			} else {
+				commands["systemd-networkd.service"] = "restart"
+			}
+		}
+
+		system.DaemonReload()
+
+		for unit, command := range commands {
+			log.Printf("Calling unit command '%s %s'", command, unit)
+			res, err := system.RunUnitCommand(command, unit)
 			if err != nil {
 				return err
 			}
-			log.Printf("Placed unit %s at %s", unit.Name, dst)
-
-			if unit.Group() != "network" {
-				log.Printf("Enabling unit file %s", dst)
-				if err := system.EnableUnitFile(dst, unit.Runtime); err != nil {
-					return err
-				}
-				log.Printf("Enabled unit %s", unit.Name)
-			} else {
-				log.Printf("Skipping enable for network-like unit %s", unit.Name)
-			}
+			log.Printf("Result of '%s %s': %s", command, unit, res)
 		}
-		system.DaemonReload()
-		system.StartUnits(cfg.Coreos.Units)
 	}
 
 	return nil

system/systemd.go

@@ -21,6 +21,7 @@ type Unit struct {
 	Name    string
 	Runtime bool
 	Content string
+	Command string
 }
 
 func (u *Unit) Type() string {
@@ -80,34 +81,33 @@ func EnableUnitFile(file string, runtime bool) error {
 	return err
 }
 
-func separateNetworkUnits(units []Unit) ([]Unit, []Unit) {
-	networkUnits := make([]Unit, 0)
-	nonNetworkUnits := make([]Unit, 0)
-	for _, unit := range units {
-		if unit.Group() == "network" {
-			networkUnits = append(networkUnits, unit)
-		} else {
-			nonNetworkUnits = append(nonNetworkUnits, unit)
-		}
-	}
-	return networkUnits, nonNetworkUnits
-}
-
-func StartUnits(units []Unit) error {
-	networkUnits, nonNetworkUnits := separateNetworkUnits(units)
-	if len(networkUnits) > 0 {
-		if err := RestartUnitByName("systemd-networkd.service"); err != nil {
-			return err
-		}
+func RunUnitCommand(command, unit string) (string, error) {
+	conn, err := dbus.New()
+	if err != nil {
+		return "", err
 	}
 
-	for _, unit := range nonNetworkUnits {
-		if err := RestartUnitByName(unit.Name); err != nil {
-			return err
-		}
+	var fn func(string, string) (string, error)
+	switch command {
+	case "start":
+		fn = conn.StartUnit
+	case "stop":
+		fn = conn.StopUnit
+	case "restart":
+		fn = conn.RestartUnit
+	case "reload":
+		fn = conn.ReloadUnit
+	case "try-restart":
+		fn = conn.TryRestartUnit
+	case "reload-or-restart":
+		fn = conn.ReloadOrRestartUnit
+	case "reload-or-try-restart":
+		fn = conn.ReloadOrTryRestartUnit
+	default:
+		return "", fmt.Errorf("Unsupported systemd command %q", command)
 	}
 
-	return nil
+	return fn(unit, "replace")
 }
 
 func DaemonReload() error {
@@ -120,19 +120,6 @@ func DaemonReload() error {
 	return err
 }
 
-func RestartUnitByName(name string) error {
-	log.Printf("Restarting unit %s", name)
-	conn, err := dbus.New()
-	if err != nil {
-		return err
-	}
-
-	output, err := conn.RestartUnit(name, "replace")
-	log.Printf("Restart completed with '%s'", output)
-
-	return err
-}
-
 func ExecuteScript(scriptPath string) (string, error) {
 	props := []dbus.Property{
 		dbus.PropDescription("Unit generated and executed by coreos-cloudinit on behalf of user"),