Adding check-only mode.

This mode allows to process template resources and run check_cmd on the result without updating target files nor running reload_cmd. This mode is useful to run monitoring checks where it's nice to be able to detect problems with the templates at rendering and application level.

config.go

@@ -41,6 +41,7 @@ var (
 	srvDomain         string
 	srvRecord         string
 	syncOnly          bool
+	checkOnly         bool
 	table             string
 	templateConfig    template.Config
 	backendsConfig    backends.Config
@@ -70,6 +71,7 @@ type Config struct {
 	SRVRecord    string   `toml:"srv_record"`
 	Scheme       string   `toml:"scheme"`
 	SyncOnly     bool     `toml:"sync-only"`
+	CheckOnly    bool     `toml:"check-only"`
 	Table        string   `toml:"table"`
 	Username     string   `toml:"username"`
 	LogLevel     string   `toml:"log-level"`
@@ -99,6 +101,7 @@ func init() {
 	flag.StringVar(&srvDomain, "srv-domain", "", "the name of the resource record")
 	flag.StringVar(&srvRecord, "srv-record", "", "the SRV record to search for backends nodes. Example: _etcd-client._tcp.example.com")
 	flag.BoolVar(&syncOnly, "sync-only", false, "sync without check_cmd and reload_cmd")
+	flag.BoolVar(&checkOnly, "check-only", false, "show pending changes and run check_cmd")
 	flag.StringVar(&authType, "auth-type", "", "Vault auth backend type to use (only used with -backend=vault)")
 	flag.StringVar(&appID, "app-id", "", "Vault app-id to use with the app-id backend (only used with -backend=vault and auth-type=app-id)")
 	flag.StringVar(&userID, "user-id", "", "Vault user-id to use with the app-id backend (only used with -backend=value and auth-type=app-id)")
@@ -228,6 +231,7 @@ func initConfig() error {
 		Noop:          config.Noop,
 		Prefix:        config.Prefix,
 		SyncOnly:      config.SyncOnly,
+		CheckOnly:     config.CheckOnly,
 		TemplateDir:   filepath.Join(config.ConfDir, "templates"),
 	}
 	return nil
@@ -308,6 +312,8 @@ func setConfigFromFlag(f *flag.Flag) {
 		config.SRVRecord = srvRecord
 	case "sync-only":
 		config.SyncOnly = syncOnly
+	case "check-only":
+		config.CheckOnly = checkOnly
 	case "table":
 		config.Table = table
 	case "username":

config_test.go

@@ -22,6 +22,7 @@ func TestInitConfigDefaultConfig(t *testing.T) {
 		SRVDomain:    "",
 		Scheme:       "http",
 		Table:        "",
+		CheckOnly:    false,
 	}
 	if err := initConfig(); err != nil {
 		t.Errorf(err.Error())

docs/check-only-mode.md

@@ -0,0 +1,34 @@
+# Check-only Mode
+
+When in check-only mode target configuration files will not be modified but `check_cmd` will be executed and execution returns error if the execution of `check_cmd` fails.
+
+This mode behaves like `noop` mode but adds the execution of the `check_cmd` command. 
+
+Note: check-only mode *does not* update target and *does not* run `reload_cmd`.
+
+## Usage
+
+### commandline flag
+
+```
+confd -check-only
+```
+
+### configuration file
+
+```
+check-only = true
+```
+
+### Example
+
+```
+confd -onetime -check-only
+```
+
+-
+
+```
+2016-06-09T15:22:28-03:00 confd[29789]: INFO /tmp/myconfig.conf has md5sum 5fc1bd8022b5cbb5aca50b74817fa9c9 should be 7cfb29f5029fc9502f58665d66ce1c6c
+2016-06-09T15:22:28-03:00 confd[29789]: WARNING Check only mode enabled. /tmp/myconfig.conf will not be modified
+```

docs/command-line-flags.md

@@ -52,6 +52,8 @@ Usage of confd:
       the SRV record to search for backends nodes. Example: _etcd-client._tcp.example.com
   -sync-only
       sync without check_cmd and reload_cmd
+  -check-only
+      show pending changes and run check_cmd.
   -table string
       the name of the DynamoDB table (only used with -backend=dynamodb)
   -user-id string

docs/configuration-guide.md

@@ -21,6 +21,7 @@ Optional:
 * `srv_domain` (string) - The name of the resource record.
 * `srv_record` (string) - The SRV record to search for backends nodes.
 * `sync-only` (bool) - sync without check_cmd and reload_cmd.
+* `check-only` (bool) - Process all template resources, run check_cmd but skip target update.
 * `watch` (bool) - Enable watch support.
 
 Example:

resource/template/resource.go

@@ -27,6 +27,7 @@ type Config struct {
 	Prefix        string
 	StoreClient   backends.StoreClient
 	SyncOnly      bool
+	CheckOnly     bool
 	TemplateDir   string
 }
 
@@ -55,6 +56,7 @@ type TemplateResource struct {
 	store         memkv.Store
 	storeClient   backends.StoreClient
 	syncOnly      bool
+	checkOnly     bool
 }
 
 var ErrEmptySrc = errors.New("empty src template")
@@ -82,6 +84,7 @@ func NewTemplateResource(path string, config Config) (*TemplateResource, error)
 	tr.funcMap = newFuncMap()
 	tr.store = memkv.New()
 	tr.syncOnly = config.SyncOnly
+	tr.checkOnly = config.CheckOnly
 	addFuncs(tr.funcMap, tr.store.FuncMap)
 
 	if config.Prefix != "" {
@@ -191,6 +194,10 @@ func (t *TemplateResource) sync() error {
 				return errors.New("Config check failed: " + err.Error())
 			}
 		}
+		if t.checkOnly {
+			log.Warning("Check only mode enabled. " + t.Dest + " will not be modified")
+			return nil
+		}
 		log.Debug("Overwriting target config " + t.Dest)
 		err := os.Rename(staged, t.Dest)
 		if err != nil {