Don't timestamp active log file

.changelog/11070.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+agent: Don't timestamp active log file.
+```

command/agent/log_file.go

@@ -62,11 +62,8 @@ func (l *logFile) fileNamePattern() string {
 }
 
 func (l *logFile) openNew() error {
-	fileNamePattern := l.fileNamePattern()
-	// New file name has the format : filename-timestamp.extension
 	createTime := now()
-	newfileName := fmt.Sprintf(fileNamePattern, strconv.FormatInt(createTime.UnixNano(), 10))
-	newfilePath := filepath.Join(l.logPath, newfileName)
+	newfilePath := filepath.Join(l.logPath, l.fileName)
 	// Try creating a file. We truncate the file because we are the only authority to write the logs
 	filePointer, err := os.OpenFile(newfilePath, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0640)
 	if err != nil {
@@ -86,8 +83,18 @@ func (l *logFile) rotate() error {
 	// Rotate if we hit the byte file limit or the time limit
 	if (l.BytesWritten >= int64(l.MaxBytes) && (l.MaxBytes > 0)) || timeElapsed >= l.duration {
 		l.FileInfo.Close()
+
+		// Move current log file to a timestamped file.
+		rotateTime := now()
+		rotatefileName := fmt.Sprintf(l.fileNamePattern(), strconv.FormatInt(rotateTime.UnixNano(), 10))
+		oldPath := l.FileInfo.Name()
+		newPath := filepath.Join(l.logPath, rotatefileName)
+		if err := os.Rename(oldPath, newPath); err != nil {
+			return fmt.Errorf("failed to rotate log files: %v", err)
+		}
+
 		if err := l.pruneFiles(); err != nil {
-			return err
+			return fmt.Errorf("failed to prune log files: %v", err)
 		}
 		return l.openNew()
 	}

command/agent/log_file_test.go

@@ -55,6 +55,8 @@ func TestLogFile_openNew(t *testing.T) {
 
 	_, err = ioutil.ReadFile(logFile.FileInfo.Name())
 	require.NoError(err)
+
+	require.Equal(logFile.FileInfo.Name(), filepath.Join(tempDir, testFileName))
 }
 
 func TestLogFile_byteRotation(t *testing.T) {

website/content/docs/configuration/index.mdx

@@ -241,9 +241,9 @@ testing.
 - `log_json` `(bool: false)` - Output logs in a JSON format.
 
 - `log_file` `(string: "")` - Specifies the path for logging. If the path
-  does not includes a filename, the filename defaults to "nomad-{timestamp}.log".
-  This setting can be combined with `log_rotate_bytes` and `log_rotate_duration`
-  for a fine-grained log rotation control.
+  does not includes a filename, the filename defaults to `nomad.log`. This
+  setting can be combined with `log_rotate_bytes` and `log_rotate_duration` for
+  a fine-grained log rotation control.
 
 - `log_rotate_bytes` `(int: 0)` - Specifies the number of bytes that should be
   written to a log before it needs to be rotated. Unless specified, there is no

website/content/docs/upgrade/upgrade-specific.mdx

@@ -13,6 +13,15 @@ upgrade. However, specific versions of Nomad may have more details provided for
 their upgrades as a result of new features or changed behavior. This page is
 used to document those details separately from the standard upgrade flow.
 
+## Nomad 1.1.4 and 1.2.0
+
+#### Log file names
+
+The [`log_file`] configuration option was not being fully respected, as the
+generated filename would include a timestamp. After upgrade, the active log
+file will always be the value defined in `log_file`, with timestamped files
+being created during log rotation.
+
 ## Nomad 1.0.9 and 1.1.3
 
 #### Namespace in Job Run and Plan APIs
@@ -1173,3 +1182,4 @@ deleted and then Nomad 0.3.0 can be launched.
 [allow_caps_java]: /docs/drivers/java#allow_caps
 [cap_add_exec]: /docs/drivers/exec#cap_add
 [cap_drop_exec]: /docs/drivers/exec#cap_drop
+[`log_file`]: /docs/configuration#log_file