admin: Implement load_interval to pull config on a timer (#4246)

* feat: implement a simple timer to pull config

mostly referenced to the issue

re #4106

* Update admin.go

use `caddy.Duration`

Co-authored-by: Matt Holt <[email protected]>

* Update caddy.go

Co-authored-by: Matt Holt <[email protected]>

* Update admin.go

Co-authored-by: Francis Lavoie <[email protected]>

* fix: sync load config when no pull interval provided

try not to make break change

* fix: change PullInterval to LoadInterval

* fix: change pull_interval to load_interval

* Update caddy.go

Co-authored-by: Matt Holt <[email protected]>

Co-authored-by: Matt Holt <[email protected]>
Co-authored-by: Francis Lavoie <[email protected]>

2 files changed, 38 insertions, 12 deletions

diff --git a/admin.go b/admin.go
index 8eef91653..ff5bc713c 100644
--- a/admin.go
+++ b/admin.go
@@ -109,6 +109,12 @@ type ConfigSettings struct {
 	//
 	// EXPERIMENTAL: Subject to change.
 	LoadRaw json.RawMessage `json:"load,omitempty" caddy:"namespace=caddy.config_loaders inline_key=module"`
+
+	// The interval to pull config. With a non-zero value, will pull config
+	// from config loader (eg. a http loader) with given interval.
+	//
+	// EXPERIMENTAL: Subject to change.
+	LoadInterval Duration `json:"load_interval,omitempty"`
 }
 
 // IdentityConfig configures management of this server's identity. An identity
diff --git a/caddy.go b/caddy.go
index 96dfea5c6..ba025b18a 100644
--- a/caddy.go
+++ b/caddy.go
@@ -268,8 +268,9 @@ func unsyncedDecodeAndRun(cfgJSON []byte, allowPersist bool) error {
 		newCfg != nil &&
 		newCfg.Admin != nil &&
 		newCfg.Admin.Config != nil &&
-		newCfg.Admin.Config.LoadRaw != nil {
-		return fmt.Errorf("recursive config loading detected: pulled configs cannot pull other configs")
+		newCfg.Admin.Config.LoadRaw != nil &&
+		newCfg.Admin.Config.LoadInterval <= 0 {
+		return fmt.Errorf("recursive config loading detected: pulled configs cannot pull other configs without positive load_interval")
 	}
 
 	// run the new config and start all its apps
@@ -480,23 +481,42 @@ func finishSettingUp(ctx Context, cfg *Config) error {
 		if err != nil {
 			return fmt.Errorf("loading config loader module: %s", err)
 		}
-		loadedConfig, err := val.(ConfigLoader).LoadConfig(ctx)
-		if err != nil {
-			return fmt.Errorf("loading dynamic config from %T: %v", val, err)
-		}
-
-		// do this in a goroutine so current config can finish being loaded; otherwise deadlock
-		go func() {
-			Log().Info("applying dynamically-loaded config", zap.String("loader_module", val.(Module).CaddyModule().ID.Name()))
+		runLoadedConfig := func(config []byte) {
+			Log().Info("applying dynamically-loaded config", zap.String("loader_module", val.(Module).CaddyModule().ID.Name()), zap.Int("pull_interval", int(cfg.Admin.Config.LoadInterval)))
 			currentCfgMu.Lock()
-			err := unsyncedDecodeAndRun(loadedConfig, false)
+			err := unsyncedDecodeAndRun(config, false)
 			currentCfgMu.Unlock()
 			if err == nil {
 				Log().Info("dynamically-loaded config applied successfully")
 			} else {
 				Log().Error("running dynamically-loaded config failed", zap.Error(err))
 			}
-		}()
+		}
+		if cfg.Admin.Config.LoadInterval > 0 {
+			go func() {
+				select {
+				// if LoadInterval is positive, will wait for the interval and then run with new config
+				case <-time.After(time.Duration(cfg.Admin.Config.LoadInterval)):
+					loadedConfig, err := val.(ConfigLoader).LoadConfig(ctx)
+					if err != nil {
+						Log().Error("loading dynamic config failed", zap.Error(err))
+						return
+					}
+					runLoadedConfig(loadedConfig)
+				case <-ctx.Done():
+					return
+				}
+			}()
+		} else {
+			// if no LoadInterval is provided, will load config synchronously
+			loadedConfig, err := val.(ConfigLoader).LoadConfig(ctx)
+			if err != nil {
+				return fmt.Errorf("loading dynamic config from %T: %v", val, err)
+			}
+			// do this in a goroutine so current config can finish being loaded; otherwise deadlock
+			go runLoadedConfig(loadedConfig)
+		}
+
 	}
 
 	return nil