Adding dry-run 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

@@ -29,6 +29,7 @@ var (
 	clientKey         string
 	confdir           string
 	config            Config // holds the global confd config.
+	dryRun            bool
 	interval          int
 	keepStageFile     bool
 	logLevel          string
@@ -62,6 +63,7 @@ type Config struct {
 	ClientCert   string   `toml:"client_cert"`
 	ClientKey    string   `toml:"client_key"`
 	ConfDir      string   `toml:"confdir"`
+	DryRun       bool     `toml:"dry-run"`
 	Interval     int      `toml:"interval"`
 	Noop         bool     `toml:"noop"`
 	Password     string   `toml:"password"`
@@ -87,6 +89,7 @@ func init() {
 	flag.StringVar(&clientKey, "client-key", "", "the client key")
 	flag.StringVar(&confdir, "confdir", "/etc/confd", "confd conf directory")
 	flag.StringVar(&configFile, "config-file", "", "the confd config file")
+	flag.BoolVar(&dryRun, "dry-run", false, "perform execution without modifying target file")
 	flag.IntVar(&interval, "interval", 600, "backend polling interval")
 	flag.BoolVar(&keepStageFile, "keep-stage-file", false, "keep staged files")
 	flag.StringVar(&logLevel, "log-level", "", "level which confd should log messages")
@@ -224,6 +227,7 @@ func initConfig() error {
 	templateConfig = template.Config{
 		ConfDir:       config.ConfDir,
 		ConfigDir:     filepath.Join(config.ConfDir, "conf.d"),
+		DryRun:        config.DryRun,
 		KeepStageFile: keepStageFile,
 		Noop:          config.Noop,
 		Prefix:        config.Prefix,
@@ -290,6 +294,8 @@ func setConfigFromFlag(f *flag.Flag) {
 		config.ClientCaKeys = clientCaKeys
 	case "confdir":
 		config.ConfDir = confdir
+	case "dry-run":
+		config.DryRun = dryRun
 	case "node":
 		config.BackendNodes = nodes
 	case "interval":

config_test.go

@@ -16,6 +16,7 @@ func TestInitConfigDefaultConfig(t *testing.T) {
 		ClientCert:   "",
 		ClientKey:    "",
 		ConfDir:      "/etc/confd",
+		DryRun:       false,
 		Interval:     600,
 		Noop:         false,
 		Prefix:       "",

docs/command-line-flags.md

@@ -28,6 +28,8 @@ Usage of confd:
       confd conf directory (default "/etc/confd")
   -config-file string
       the confd config file
+  -dry-run
+      show pending changes and run check_cmd.
   -interval int
       backend polling interval (default 600)
   -keep-stage-file

docs/configuration-guide.md

@@ -12,6 +12,7 @@ Optional:
 * `client_cert` (string) - The client cert file.
 * `client_key` (string) - The client key file.
 * `confdir` (string) - The path to confd configs. ("/etc/confd")
+* `dry-run` (bool) - Process all template resources, run check_cmd but skip target update.
 * `interval` (int) - The backend polling interval in seconds. (600)
 * `log-level` (string) - level which confd should log messages ("info")
 * `nodes` (array of strings) - List of backend nodes. (["http://127.0.0.1:4001"])

docs/dry-run-mode.md

@@ -0,0 +1,34 @@
+# Dry-Run Mode
+
+When in dry-run 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: dry-run mode *does not* update target and *does not* run `reload_cmd`.
+
+## Usage
+
+### commandline flag
+
+```
+confd -dry-run
+```
+
+### configuration file
+
+```
+dry-run = true
+```
+
+### Example
+
+```
+confd -onetime -dry-run
+```
+
+-
+
+```
+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 Dry-run mode enabled. /tmp/myconfig.conf will not be modified
+```

resource/template/resource.go

@@ -22,6 +22,7 @@ import (
 type Config struct {
 	ConfDir       string
 	ConfigDir     string
+	DryRun        bool
 	KeepStageFile bool
 	Noop          bool
 	Prefix        string
@@ -55,6 +56,7 @@ type TemplateResource struct {
 	store         memkv.Store
 	storeClient   backends.StoreClient
 	syncOnly      bool
+	dryRun        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.dryRun = config.DryRun
 	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.dryRun {
+			log.Warning("Dry-run 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 {