Export the error details to an error file

The current git-sync process outputs the error information to standard
out, which is inaccessible from outside the container. Users have to
dump the logs using kubectl logs in order to check the error details in
the git-sync process. This commit exports the error details to a file,
which provides users the capability to check the errors directly from
other sidecar containers.

proposal: #326

Author: nan-yu

cmd/git-sync/main.go

@@ -21,6 +21,7 @@ package main // import "k8s.io/git-sync/cmd/git-sync"
 import (
 	"bytes"
 	"context"
+	"encoding/json"
 	"flag"
 	"fmt"
 	"io/ioutil"
@@ -37,6 +38,7 @@ import (
 	"time"
 
 	"github.com/go-logr/glogr"
+	"github.com/go-logr/logr"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"k8s.io/git-sync/pkg/pid1"
@@ -60,6 +62,8 @@ var flRoot = flag.String("root", envString("GIT_SYNC_ROOT", envString("HOME", ""
 	"the root directory for git-sync operations, under which --dest will be created")
 var flDest = flag.String("dest", envString("GIT_SYNC_DEST", ""),
 	"the name of (a symlink to) a directory in which to check-out files under --root (defaults to the leaf dir of --repo)")
+var flErrorFile = flag.String("error-file", envString("GIT_SYNC_ERROR_FILE", ""),
+	"the name of a file into which errors will be written under --root (defaults to \"\", disabling error reporting)")
 var flWait = flag.Float64("wait", envFloat("GIT_SYNC_WAIT", 1),
 	"the number of seconds between syncs")
 var flSyncTimeout = flag.Int("timeout", envInt("GIT_SYNC_TIMEOUT", 120),
@@ -119,7 +123,7 @@ var flHTTPMetrics = flag.Bool("http-metrics", envBool("GIT_SYNC_HTTP_METRICS", t
 var flHTTPprof = flag.Bool("http-pprof", envBool("GIT_SYNC_HTTP_PPROF", false),
 	"enable the pprof debug endpoints on git-sync's HTTP endpoint")
 
-var log = glogr.New()
+var log *customLogger
 
 // Total pull/error, summary on pull duration
 var (
@@ -155,6 +159,90 @@ const (
 	submodulesOff       = "off"
 )
 
+type customLogger struct {
+	logr.Logger
+	errorFile string
+}
+
+func (l customLogger) Error(err error, msg string, kvList ...interface{}) {
+	l.Logger.Error(err, msg, kvList...)
+	if l.errorFile == "" {
+		return
+	}
+	payload := struct {
+		Msg  string
+		Err  string
+		Args map[string]interface{}
+	}{
+		Msg:  msg,
+		Err:  err.Error(),
+		Args: map[string]interface{}{},
+	}
+	if len(kvList)%2 != 0 {
+		kvList = append(kvList, "<no-value>")
+	}
+	for i := 0; i < len(kvList); i += 2 {
+		k, ok := kvList[i].(string)
+		if !ok {
+			k = fmt.Sprintf("%v", kvList[i])
+		}
+		payload.Args[k] = kvList[i+1]
+	}
+	jb, err := json.Marshal(payload)
+	if err != nil {
+		l.Logger.Error(err, "can't encode error payload")
+		content := fmt.Sprintf("%v", err)
+		l.writeContent([]byte(content))
+	} else {
+		l.writeContent(jb)
+	}
+}
+
+// exportError exports the error to the error file if --export-error is enabled.
+func (l *customLogger) exportError(content string) {
+	if l.errorFile == "" {
+		return
+	}
+	l.writeContent([]byte(content))
+}
+
+// writeContent writes the error content to the error file.
+func (l *customLogger) writeContent(content []byte) {
+	tmpFile, err := ioutil.TempFile(*flRoot, "tmp-err-")
+	if err != nil {
+		l.Logger.Error(err, "can't create temporary error-file", "directory", *flRoot, "prefix", "tmp-err-")
+		return
+	}
+	defer func() {
+		if err := tmpFile.Close(); err != nil {
+			l.Logger.Error(err, "can't close temporary error-file", "filename", tmpFile.Name())
+		}
+	}()
+
+	if _, err = tmpFile.Write(content); err != nil {
+		l.Logger.Error(err, "can't write to temporary error-file", "filename", tmpFile.Name())
+		return
+	}
+
+	if err := os.Rename(tmpFile.Name(), l.errorFile); err != nil {
+		l.Logger.Error(err, "can't rename to error-file", "temp-file", tmpFile.Name(), "error-file", l.errorFile)
+		return
+	}
+}
+
+// deleteErrorFile deletes the error file.
+func (l *customLogger) deleteErrorFile() {
+	if l.errorFile == "" {
+		return
+	}
+	if err := os.Remove(l.errorFile); err != nil {
+		if os.IsNotExist(err) {
+			return
+		}
+		l.Logger.Error(err, "can't delete the error-file", "filename", l.errorFile)
+	}
+}
+
 func init() {
 	prometheus.MustRegister(syncDuration)
 	prometheus.MustRegister(syncCount)
@@ -184,7 +272,7 @@ func envInt(key string, def int) int {
 	if env := os.Getenv(key); env != "" {
 		val, err := strconv.ParseInt(env, 0, 0)
 		if err != nil {
-			log.Error(err, "invalid env value, using default", "key", key, "val", os.Getenv(key), "default", def)
+			fmt.Fprintf(os.Stderr, "WARNING: invalid env value (%v): using default, key=%s, val=%q, default=%d\n", err, key, env, def)
 			return def
 		}
 		return int(val)
@@ -196,7 +284,7 @@ func envFloat(key string, def float64) float64 {
 	if env := os.Getenv(key); env != "" {
 		val, err := strconv.ParseFloat(env, 64)
 		if err != nil {
-			log.Error(err, "invalid env value, using default", "key", key, "val", os.Getenv(key), "default", def)
+			fmt.Fprintf(os.Stderr, "WARNING: invalid env value (%v): using default, key=%s, val=%q, default=%f\n", err, key, env, def)
 			return def
 		}
 		return val
@@ -208,7 +296,7 @@ func envDuration(key string, def time.Duration) time.Duration {
 	if env := os.Getenv(key); env != "" {
 		val, err := time.ParseDuration(env)
 		if err != nil {
-			log.Error(err, "invalid env value, using default", "key", key, "val", os.Getenv(key), "default", def)
+			fmt.Fprintf(os.Stderr, "WARNING: invalid env value (%v): using default, key=%s, val=%q, default=%d\n", err, key, env, def)
 			return def
 		}
 		return val
@@ -220,8 +308,7 @@ func setFlagDefaults() {
 	// Force logging to stderr (from glog).
 	stderrFlag := flag.Lookup("logtostderr")
 	if stderrFlag == nil {
-		fmt.Fprintf(os.Stderr, "ERROR: can't find flag 'logtostderr'\n")
-		os.Exit(1)
+		handleError(false, "ERROR: can't find flag 'logtostderr'")
 	}
 	stderrFlag.Value.Set("true")
 }
@@ -241,35 +328,33 @@ func main() {
 	setFlagDefaults()
 	flag.Parse()
 
+	var errorFile string
+	if *flErrorFile != "" {
+		errorFile = filepath.Join(*flRoot, *flErrorFile)
+	}
+	log = &customLogger{glogr.New(), errorFile}
+
 	if *flVer {
 		fmt.Println(version.VERSION)
 		os.Exit(0)
 	}
 
 	if *flRepo == "" {
-		fmt.Fprintf(os.Stderr, "ERROR: --repo must be specified\n")
-		flag.Usage()
-		os.Exit(1)
+		handleError(true, "ERROR: --repo must be specified")
 	}
 
 	if *flDepth < 0 { // 0 means "no limit"
-		fmt.Fprintf(os.Stderr, "ERROR: --depth must be greater than or equal to 0\n")
-		flag.Usage()
-		os.Exit(1)
+		handleError(true, "ERROR: --depth must be greater than or equal to 0")
 	}
 
 	switch *flSubmodules {
 	case submodulesRecursive, submodulesShallow, submodulesOff:
 	default:
-		fmt.Fprintf(os.Stderr, "ERROR: --submodules must be one of %q, %q, or %q", submodulesRecursive, submodulesShallow, submodulesOff)
-		flag.Usage()
-		os.Exit(1)
+		handleError(true, "ERROR: --submodules must be one of %q, %q, or %q", submodulesRecursive, submodulesShallow, submodulesOff)
 	}
 
 	if *flRoot == "" {
-		fmt.Fprintf(os.Stderr, "ERROR: --root must be specified\n")
-		flag.Usage()
-		os.Exit(1)
+		handleError(true, "ERROR: --root must be specified")
 	}
 
 	if *flDest == "" {
@@ -278,81 +363,59 @@ func main() {
 	}
 
 	if strings.Contains(*flDest, "/") {
-		fmt.Fprintf(os.Stderr, "ERROR: --dest must be a leaf name, not a path\n")
-		flag.Usage()
-		os.Exit(1)
+		handleError(true, "ERROR: --dest must be a leaf name, not a path")
 	}
 
 	if *flWait < 0 {
-		fmt.Fprintf(os.Stderr, "ERROR: --wait must be greater than or equal to 0\n")
-		flag.Usage()
-		os.Exit(1)
+		handleError(true, "ERROR: --wait must be greater than or equal to 0")
 	}
 
 	if *flSyncTimeout < 0 {
-		fmt.Fprintf(os.Stderr, "ERROR: --timeout must be greater than 0\n")
-		flag.Usage()
-		os.Exit(1)
+		handleError(true, "ERROR: --timeout must be greater than 0")
 	}
 
 	if *flWebhookURL != "" {
 		if *flWebhookStatusSuccess < -1 {
-			fmt.Fprintf(os.Stderr, "ERROR: --webhook-success-status must be a valid HTTP code or -1\n")
-			flag.Usage()
-			os.Exit(1)
+			handleError(true, "ERROR: --webhook-success-status must be a valid HTTP code or -1")
 		}
 		if *flWebhookTimeout < time.Second {
-			fmt.Fprintf(os.Stderr, "ERROR: --webhook-timeout must be at least 1s\n")
-			flag.Usage()
-			os.Exit(1)
+			handleError(true, "ERROR: --webhook-timeout must be at least 1s")
 		}
 		if *flWebhookBackoff < time.Second {
-			fmt.Fprintf(os.Stderr, "ERROR: --webhook-backoff must be at least 1s\n")
-			flag.Usage()
-			os.Exit(1)
+			handleError(true, "ERROR: --webhook-backoff must be at least 1s")
 		}
 	}
 
 	if _, err := exec.LookPath(*flGitCmd); err != nil {
-		fmt.Fprintf(os.Stderr, "ERROR: git executable %q not found: %v\n", *flGitCmd, err)
-		os.Exit(1)
+		handleError(false, "ERROR: git executable %q not found: %v", *flGitCmd, err)
 	}
 
 	if *flSSH {
 		if *flUsername != "" {
-			fmt.Fprintf(os.Stderr, "ERROR: only one of --ssh and --username may be specified\n")
-			os.Exit(1)
+			handleError(false, "ERROR: only one of --ssh and --username may be specified")
 		}
 		if *flPassword != "" {
-			fmt.Fprintf(os.Stderr, "ERROR: only one of --ssh and --password may be specified\n")
-			os.Exit(1)
+			handleError(false, "ERROR: only one of --ssh and --password may be specified")
 		}
 		if *flAskPassURL != "" {
-			fmt.Fprintf(os.Stderr, "ERROR: only one of --ssh and --askpass-url may be specified\n")
-			os.Exit(1)
+			handleError(false, "ERROR: only one of --ssh and --askpass-url may be specified")
 		}
 		if *flCookieFile {
-			fmt.Fprintf(os.Stderr, "ERROR: only one of --ssh and --cookie-file may be specified\n")
-			os.Exit(1)
+			handleError(false, "ERROR: only one of --ssh and --cookie-file may be specified")
 		}
 		if *flSSHKeyFile == "" {
-			fmt.Fprintf(os.Stderr, "ERROR: --ssh-key-file must be specified when --ssh is specified\n")
-			flag.Usage()
-			os.Exit(1)
+			handleError(true, "ERROR: --ssh-key-file must be specified when --ssh is specified")
 		}
 		if *flSSHKnownHosts {
 			if *flSSHKnownHostsFile == "" {
-				fmt.Fprintf(os.Stderr, "ERROR: --ssh-known-hosts-file must be specified when --ssh-known-hosts is specified\n")
-				flag.Usage()
-				os.Exit(1)
+				handleError(true, "ERROR: --ssh-known-hosts-file must be specified when --ssh-known-hosts is specified")
 			}
 		}
 	}
 
 	if *flAddUser {
 		if err := addUser(); err != nil {
-			fmt.Fprintf(os.Stderr, "ERROR: can't write to /etc/passwd: %v\n", err)
-			os.Exit(1)
+			handleError(false, "ERROR: can't write to /etc/passwd: %v", err)
 		}
 	}
 
@@ -362,30 +425,26 @@ func main() {
 
 	if *flUsername != "" && *flPassword != "" {
 		if err := setupGitAuth(ctx, *flUsername, *flPassword, *flRepo); err != nil {
-			fmt.Fprintf(os.Stderr, "ERROR: can't create .netrc file: %v\n", err)
-			os.Exit(1)
+			handleError(false, "ERROR: can't create .netrc file: %v", err)
 		}
 	}
 
 	if *flSSH {
 		if err := setupGitSSH(*flSSHKnownHosts); err != nil {
-			fmt.Fprintf(os.Stderr, "ERROR: can't configure SSH: %v\n", err)
-			os.Exit(1)
+			handleError(false, "ERROR: can't configure SSH: %v", err)
 		}
 	}
 
 	if *flCookieFile {
 		if err := setupGitCookieFile(ctx); err != nil {
-			fmt.Fprintf(os.Stderr, "ERROR: can't set git cookie file: %v\n", err)
-			os.Exit(1)
+			handleError(false, "ERROR: can't set git cookie file: %v", err)
 		}
 	}
 
 	if *flAskPassURL != "" {
 		if err := callGitAskPassURL(ctx, *flAskPassURL); err != nil {
 			askpassCount.WithLabelValues(metricKeyError).Inc()
-			fmt.Fprintf(os.Stderr, "ERROR: failed to call ASKPASS callback URL: %v\n", err)
-			os.Exit(1)
+			handleError(false, "ERROR: failed to call ASKPASS callback URL: %v", err)
 		}
 		askpassCount.WithLabelValues(metricKeySuccess).Inc()
 	}
@@ -404,8 +463,7 @@ func main() {
 	if *flHTTPBind != "" {
 		ln, err := net.Listen("tcp", *flHTTPBind)
 		if err != nil {
-			fmt.Fprintf(os.Stderr, "ERROR: unable to bind HTTP endpoint: %v\n", err)
-			os.Exit(1)
+			handleError(false, "ERROR: unable to bind HTTP endpoint: %v", err)
 		}
 		mux := http.NewServeMux()
 		go func() {
@@ -480,19 +538,22 @@ func main() {
 
 		if initialSync {
 			if *flOneTime {
+				log.deleteErrorFile()
 				os.Exit(0)
 			}
 			if isHash, err := revIsHash(ctx, *flRev, *flRoot); err != nil {
 				log.Error(err, "can't tell if rev is a git hash, exiting", "rev", *flRev)
 				os.Exit(1)
 			} else if isHash {
 				log.V(0).Info("rev appears to be a git hash, no further sync needed", "rev", *flRev)
+				log.deleteErrorFile()
 				sleepForever()
 			}
 			initialSync = false
 		}
 
 		failCount = 0
+		log.deleteErrorFile()
 		log.V(1).Info("next sync", "wait_time", waitTime(*flWait))
 		cancel()
 		time.Sleep(waitTime(*flWait))
@@ -517,6 +578,18 @@ func sleepForever() {
 	os.Exit(0)
 }
 
+// handleError prints the error to the standard error, prints the usage if the `printUsage` flag is true,
+// exports the error to the error file and exits the process with the exit code.
+func handleError(printUsage bool, format string, a ...interface{}) {
+	s := fmt.Sprintf(format, a...)
+	fmt.Fprintln(os.Stderr, s)
+	if printUsage {
+		flag.Usage()
+	}
+	log.exportError(s)
+	os.Exit(1)
+}
+
 // Put the current UID/GID into /etc/passwd so SSH can look it up.  This
 // assumes that we have the permissions to write to it.
 func addUser() error {