feat(initialize): add locksmith configuration

configure locksmith strategy based on the cloud config.

Documentation/cloud-config.md

@@ -70,6 +70,23 @@ Note that hyphens in the coreos.etcd.* keys are mapped to underscores.
 
 [etcd-config]: https://github.com/coreos/etcd/blob/master/Documentation/configuration.md
 
+#### update
+
+The `coreos.update.*` parameters manipulate settings related to how CoreOS instances are updated.
+
+- **reboot-strategy**: One of "reboot", "etcd-lock", "best-effort" or "off" for controlling when reboots are issued after an update is performed.
+  - _reboot_: Reboot immediately after an update is applied.
+  - _etcd-lock_: Reboot after first taking a distributed lock in etcd, this guarantees that only one host will reboot concurrently and that the cluster will remain available during the update.
+  - _best-effort_ - If etcd is running, "etcd-lock", otherwise simply "reboot".
+  - _off_ - Disable rebooting after updates are applied (not recommended).
+
+```
+#cloud-config
+coreos:
+  update:
+    reboot-strategy: etcd-lock
+```
+
 #### oem
 
 The `coreos.oem.*` parameters follow the [os-release spec][os-release], but have been repurposed as a way for coreos-cloudinit to know about the OEM partition on this machine:

initialize/config.go

@@ -13,9 +13,10 @@ import (
 type CloudConfig struct {
 	SSHAuthorizedKeys []string `yaml:"ssh_authorized_keys"`
 	Coreos            struct {
-		Etcd  EtcdEnvironment
-		Units []system.Unit
-		OEM   OEMRelease
+		Etcd   EtcdEnvironment
+		Update map[string]string
+		Units  []system.Unit
+		OEM    OEMRelease
 	}
 	WriteFiles     []system.File `yaml:"write_files"`
 	Hostname       string
@@ -128,6 +129,13 @@ func Apply(cfg CloudConfig, env *Environment) error {
 		log.Printf("Wrote etcd config file to filesystem")
 	}
 
+	if s, ok := cfg.Coreos.Update["reboot-strategy"]; ok {
+		if err := WriteLocksmithEnvironment(s, env.Root()); err != nil {
+			log.Fatalf("Failed to write locksmith config to filesystem: %v", err)
+		}
+		log.Printf("Wrote locksmith config file to filesystem")
+	}
+
 	if len(cfg.Coreos.Units) > 0 {
 		commands := make(map[string]string, 0)
 		for _, unit := range cfg.Coreos.Units {

initialize/config_test.go

@@ -32,6 +32,8 @@ func TestCloudConfig(t *testing.T) {
 coreos: 
   etcd:
     discovery: "https://discovery.etcd.io/827c73219eeb2fa5530027c37bf18877"
+  update:
+    reboot-strategy: reboot
   units:
     - name: 50-eth0.network
       runtime: yes
@@ -129,6 +131,9 @@ Address=10.209.171.177/19
 	if cfg.Hostname != "trontastic" {
 		t.Errorf("Failed to parse hostname")
 	}
+	if cfg.Coreos.Update["reboot-strategy"] != "reboot" {
+		t.Errorf("Failed to parse locksmith strategy")
+	}
 }
 
 // Assert that our interface conversion doesn't panic

initialize/locksmith.go

@@ -0,0 +1,82 @@
+package initialize
+
+import (
+	"bufio"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path"
+	"strings"
+
+	"github.com/coreos/coreos-cloudinit/system"
+)
+
+const locksmithUnit = "locksmithd.service"
+
+// addStrategy creates an `/etc/coreos/update.conf` file with the requested
+// strategy via rewriting the file on disk or by starting from
+// `/usr/share/coreos/update.conf`.
+func addStrategy(strategy string, root string) error {
+	etcUpdate := path.Join(root, "etc", "coreos", "update.conf")
+	usrUpdate := path.Join(root, "usr", "share", "coreos", "update.conf")
+
+	tmp, err := ioutil.TempFile(path.Join(root, "etc", "coreos"), ".update.conf")
+	if err != nil {
+		return err
+	}
+	err = tmp.Chmod(0644)
+	if err != nil {
+		return err
+	}
+
+	conf, err := os.Open(etcUpdate)
+	if os.IsNotExist(err) {
+		conf, err = os.Open(usrUpdate)
+		if err != nil {
+			return err
+		}
+	}
+
+	scanner := bufio.NewScanner(conf)
+
+	sawStrat := false
+	stratLine := "STRATEGY="+strategy
+	for scanner.Scan() {
+		line := scanner.Text()
+		if strings.HasPrefix(line, "STRATEGY=") {
+			line = stratLine
+			sawStrat = true
+		}
+		fmt.Fprintln(tmp, line)
+		if err := scanner.Err(); err != nil {
+			return err
+		}
+	}
+
+	if !sawStrat {
+		fmt.Fprintln(tmp, stratLine)
+	}
+
+	return os.Rename(tmp.Name(), etcUpdate)
+}
+
+// WriteLocksmithEnvironment writes a drop-in unit for locksmith
+func WriteLocksmithEnvironment(strategy string, root string) error {
+	cmd := "restart"
+	if strategy == "off" {
+		err := system.MaskUnit(locksmithUnit, root)
+		if err != nil {
+			return err
+		}
+		cmd = "stop"
+	} else {
+		return addStrategy(strategy, root)
+	}
+	if err := system.DaemonReload(); err != nil {
+		return err
+	}
+	if _, err := system.RunUnitCommand(cmd, locksmithUnit); err != nil {
+		return err
+	}
+	return nil
+}

initialize/locksmith_test.go

@@ -0,0 +1,92 @@
+package initialize
+
+import (
+	"io/ioutil"
+	"os"
+	"path"
+	"testing"
+)
+
+const (
+	base = `SERVER=https://example.com
+GROUP=thegroupc`
+
+	configured = base + `
+STRATEGY=awesome
+`
+
+	expected = base + `
+STRATEGY=etcd-lock
+`
+)
+
+func setupFixtures(dir string) {
+	os.MkdirAll(path.Join(dir, "usr", "share", "coreos"), 0755)
+	os.MkdirAll(path.Join(dir, "etc", "coreos"), 0755)
+	os.MkdirAll(path.Join(dir, "run", "systemd", "system"), 0755)
+
+	ioutil.WriteFile(path.Join(dir, "usr", "share", "coreos", "update.conf"), []byte(base), 0644)
+}
+
+func TestLocksmithEnvironmentWrittenToDisk(t *testing.T) {
+	dir, err := ioutil.TempDir(os.TempDir(), "coreos-cloudinit-")
+	if err != nil {
+		t.Fatalf("Unable to create tempdir: %v", err)
+	}
+	defer os.RemoveAll(dir)
+	setupFixtures(dir)
+
+	for i := 0; i < 2; i++ {
+		if i == 1 {
+			err = ioutil.WriteFile(path.Join(dir, "etc", "coreos", "update.conf"), []byte(configured), 0644)
+			if err != nil {
+				t.Fatal(err)
+			}
+		}
+
+		if err := WriteLocksmithEnvironment("etcd-lock", dir); err != nil {
+			t.Fatalf("Processing of LocksmithEnvironment failed: %v", err)
+		}
+
+		fullPath := path.Join(dir, "etc", "coreos", "update.conf")
+
+		fi, err := os.Stat(fullPath)
+		if err != nil {
+			t.Fatalf("Unable to stat file: %v", err)
+		}
+
+		if fi.Mode() != os.FileMode(0644) {
+			t.Errorf("File has incorrect mode: %v", fi.Mode())
+		}
+
+		contents, err := ioutil.ReadFile(fullPath)
+		if err != nil {
+			t.Fatalf("Unable to read expected file: %v", err)
+		}
+
+		if string(contents) != expected {
+			t.Fatalf("File has incorrect contents, got %v, wanted %v", string(contents), expected)
+		}
+	}
+}
+func TestLocksmithEnvironmentMasked(t *testing.T) {
+	dir, err := ioutil.TempDir(os.TempDir(), "coreos-cloudinit-")
+	if err != nil {
+		t.Fatalf("Unable to create tempdir: %v", err)
+	}
+	defer os.RemoveAll(dir)
+	setupFixtures(dir)
+
+	if err := WriteLocksmithEnvironment("off", dir); err != nil {
+		t.Fatalf("Processing of LocksmithEnvironment failed: %v", err)
+	}
+
+	fullPath := path.Join(dir, "etc", "systemd", "system", "locksmithd.service")
+	target, err := os.Readlink(fullPath)
+	if err != nil {
+		t.Fatalf("Unable to read link %v", err)
+	}
+	if target != "/dev/null" {
+		t.Fatalf("Locksmith not masked, unit target %v", target)
+	}
+}