From bfa612ccee38143a3a288d7c7bc101846ca63e58 Mon Sep 17 00:00:00 2001
From: hc-github-team-consul-core <github-team-consul-core@hashicorp.com>
Date: Mon, 4 Sep 2023 05:13:31 -0500
Subject: [PATCH] Backport of NET-3181 - Allow log file naming like Nomad into
 release/1.15.x (#18629)

* backport of commit a5ad3664038a3dd225b5c14b3adc181fb4dd61a6

* backport of commit 24e7b9b9602b83dd67096a61b9305a37c6d77801

* NET-3181 - Allow log file naming like Nomad (#18617)

* fixes file name for consul

* added log file

* added tests for rename method

---------

Co-authored-by: absolutelightning <ashesh.vidyut@hashicorp.com>
Co-authored-by: Ashesh Vidyut <134911583+absolutelightning@users.noreply.github.com>
---
 .changelog/18617.txt    |  4 ++++
 logging/logfile.go      | 20 +++++++++++++++++---
 logging/logfile_test.go | 16 ++++++++++++++++
 3 files changed, 37 insertions(+), 3 deletions(-)
 create mode 100644 .changelog/18617.txt

diff --git a/.changelog/18617.txt b/.changelog/18617.txt
new file mode 100644
index 0000000000..1f840d836d
--- /dev/null
+++ b/.changelog/18617.txt
@@ -0,0 +1,4 @@
+```release-note:improvement
+log: Currently consul logs files like this consul-{timestamp}.log. This change makes sure that there is always
+consul.log file with the latest logs in it.
+```
\ No newline at end of file
diff --git a/logging/logfile.go b/logging/logfile.go
index fbd1d2b707..12cf86d14b 100644
--- a/logging/logfile.go
+++ b/logging/logfile.go
@@ -57,10 +57,8 @@ func (l *LogFile) fileNamePattern() string {
 }
 
 func (l *LogFile) openNew() error {
-	fileNamePattern := l.fileNamePattern()
-
 	createTime := now()
-	newfileName := fmt.Sprintf(fileNamePattern, strconv.FormatInt(createTime.UnixNano(), 10))
+	newfileName := l.fileName
 	newfilePath := filepath.Join(l.logPath, newfileName)
 
 	// Try creating a file. We truncate the file because we are the only authority to write the logs
@@ -76,12 +74,28 @@ func (l *LogFile) openNew() error {
 	return nil
 }
 
+func (l *LogFile) renameCurrentFile() error {
+	fileNamePattern := l.fileNamePattern()
+
+	createTime := now()
+	// Current file is consul.log always
+	currentFilePath := filepath.Join(l.logPath, l.fileName)
+
+	oldFileName := fmt.Sprintf(fileNamePattern, strconv.FormatInt(createTime.UnixNano(), 10))
+	oldFilePath := filepath.Join(l.logPath, oldFileName)
+
+	return os.Rename(currentFilePath, oldFilePath)
+}
+
 func (l *LogFile) rotate() error {
 	// Get the time from the last point of contact
 	timeElapsed := time.Since(l.LastCreated)
 	// 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()
+		if err := l.renameCurrentFile(); err != nil {
+			return err
+		}
 		if err := l.pruneFiles(); err != nil {
 			return err
 		}
diff --git a/logging/logfile_test.go b/logging/logfile_test.go
index 09313a67cb..64b051fda6 100644
--- a/logging/logfile_test.go
+++ b/logging/logfile_test.go
@@ -48,6 +48,22 @@ func TestLogFile_openNew(t *testing.T) {
 	require.Contains(t, string(content), msg)
 }
 
+func TestLogFile_renameCurrentFile(t *testing.T) {
+	logFile := LogFile{
+		fileName: "consul.log",
+		logPath:  testutil.TempDir(t, ""),
+		duration: defaultRotateDuration,
+	}
+	err := logFile.openNew()
+	require.NoError(t, err)
+
+	err = logFile.renameCurrentFile()
+	require.NoError(t, err)
+
+	_, err = os.ReadFile(logFile.FileInfo.Name())
+	require.Contains(t, err.Error(), "no such file or directory")
+}
+
 func TestLogFile_Rotation_MaxBytes(t *testing.T) {
 	tempDir := testutil.TempDir(t, "LogWriterBytes")
 	logFile := LogFile{