admin listener as opt-in for initial config (#2834)

* Always cleanup admin endpoint first

* Error out if no config has been set (#2833)

* Ignore explicitly missing admin config (#2833)

* Separate config loading from admin initialization (#2833)

* Add admin option to specify admin listener address (#2833)

* Use zap for reporting admin endpoint status

4 files changed, 55 insertions, 20 deletions

diff --git a/admin.go b/admin.go
index 0b4affd..e48a4ca 100644
--- a/admin.go
+++ b/admin.go
@@ -18,6 +18,7 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -42,6 +43,8 @@ var (
 	cfgEndptSrvMu sync.Mutex
 )
 
+var ErrAdminInterfaceNotConfigured = errors.New("no admin configuration has been set")
+
 // AdminConfig configures the admin endpoint.
 type AdminConfig struct {
 	Listen string `json:"listen,omitempty"`
@@ -60,10 +63,24 @@ var DefaultAdminConfig = &AdminConfig{
 // in the format of JSON bytes. It opens a listener
 // resource. When no longer needed, StopAdmin should
 // be called.
+// If no configuration is given, a default listener is
+// started. If a configuration is given that does NOT
+// specifically configure the admin interface,
+// `ErrAdminInterfaceNotConfigured` is returned and no
+// listener is initialized.
 func StartAdmin(initialConfigJSON []byte) error {
 	cfgEndptSrvMu.Lock()
 	defer cfgEndptSrvMu.Unlock()
 
+	if cfgEndptSrv != nil {
+		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+		defer cancel()
+		err := cfgEndptSrv.Shutdown(ctx)
+		if err != nil {
+			return fmt.Errorf("shutting down old admin endpoint: %v", err)
+		}
+	}
+
 	adminConfig := DefaultAdminConfig
 	if len(initialConfigJSON) > 0 {
 		var config *Config
@@ -71,16 +88,11 @@ func StartAdmin(initialConfigJSON []byte) error {
 		if err != nil {
 			return fmt.Errorf("unmarshaling bootstrap config: %v", err)
 		}
-		if config != nil && config.Admin != nil {
-			adminConfig = config.Admin
-		}
-		if cfgEndptSrv != nil {
-			ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
-			defer cancel()
-			err := cfgEndptSrv.Shutdown(ctx)
-			if err != nil {
-				return fmt.Errorf("shutting down old admin endpoint: %v", err)
+		if config != nil {
+			if config.Admin == nil {
+				return ErrAdminInterfaceNotConfigured
 			}
+			adminConfig = config.Admin
 		}
 	}
 
@@ -136,15 +148,7 @@ func StartAdmin(initialConfigJSON []byte) error {
 
 	go cfgEndptSrv.Serve(ln)
 
-	fmt.Println("Caddy 2 admin endpoint listening on", adminConfig.Listen)
-
-	if len(initialConfigJSON) > 0 {
-		err := Load(bytes.NewReader(initialConfigJSON))
-		if err != nil {
-			return fmt.Errorf("loading initial config: %v", err)
-		}
-		fmt.Println("Caddy 2 serving initial configuration")
-	}
+	Log().Named("admin").Info("Caddy 2 admin endpoint started.", zap.String("listenAddress", adminConfig.Listen))
 
 	return nil
 }
diff --git a/caddyconfig/httpcaddyfile/httptype.go b/caddyconfig/httpcaddyfile/httptype.go
index bc546b4..05022d1 100644
--- a/caddyconfig/httpcaddyfile/httptype.go
+++ b/caddyconfig/httpcaddyfile/httptype.go
@@ -74,6 +74,8 @@ func (st ServerType) Setup(originalServerBlocks []caddyfile.ServerBlock,
 				val, err = parseOptACMECA(disp)
 			case "email":
 				val, err = parseOptEmail(disp)
+			case "admin":
+				val, err = parseOptAdmin(disp)
 			default:
 				return nil, warnings, fmt.Errorf("unrecognized parameter name: %s", dir)
 			}
@@ -254,6 +256,9 @@ func (st ServerType) Setup(originalServerBlocks []caddyfile.ServerBlock,
 			storageCvtr.(caddy.Module).CaddyModule().ID(),
 			&warnings)
 	}
+	if adminConfig, ok := options["admin"].(string); ok && adminConfig != "" {
+		cfg.Admin = &caddy.AdminConfig{Listen: adminConfig}
+	}
 
 	return cfg, warnings, nil
 }
diff --git a/caddyconfig/httpcaddyfile/options.go b/caddyconfig/httpcaddyfile/options.go
index a60d060..74ec507 100644
--- a/caddyconfig/httpcaddyfile/options.go
+++ b/caddyconfig/httpcaddyfile/options.go
@@ -132,3 +132,17 @@ func parseOptEmail(d *caddyfile.Dispenser) (string, error) {
 	}
 	return val, nil
 }
+
+func parseOptAdmin(d *caddyfile.Dispenser) (string, error) {
+	if d.Next() {
+		var listenAddress string
+		d.AllArgs(&listenAddress)
+
+		if listenAddress == "" {
+			listenAddress = caddy.DefaultAdminListen
+		}
+
+		return listenAddress, nil
+	}
+	return "", nil
+}
diff --git a/cmd/commandfuncs.go b/cmd/commandfuncs.go
index 7c08c2e..d73644c 100644
--- a/cmd/commandfuncs.go
+++ b/cmd/commandfuncs.go
@@ -161,12 +161,24 @@ func cmdRun(fl Flags) (int, error) {
 	certmagic.UserAgent = "Caddy/" + cleanModVersion
 
 	// start the admin endpoint along with any initial config
+	// a configuration without admin config is considered fine
+	// but does not enable the admin endpoint at all
 	err = caddy.StartAdmin(config)
-	if err != nil {
+	if err == nil {
+		defer caddy.StopAdmin()
+	} else if err != caddy.ErrAdminInterfaceNotConfigured {
 		return caddy.ExitCodeFailedStartup,
 			fmt.Errorf("starting caddy administration endpoint: %v", err)
 	}
-	defer caddy.StopAdmin()
+
+	// if a config has been supplied, load it as initial config
+	if len(config) > 0 {
+		err := caddy.Load(bytes.NewReader(config))
+		if err != nil {
+			return caddy.ExitCodeFailedStartup, fmt.Errorf("loading initial config: %v", err)
+		}
+		caddy.Log().Named("admin").Info("Caddy 2 serving initial configuration")
+	}
 
 	// if we are to report to another process the successful start
 	// of the server, do so now by echoing back contents of stdin