Add file rotation based on file age to file output plugin

plugins/outputs/file/README.md

@@ -8,6 +8,9 @@ This plugin writes telegraf metrics to files
   ## Files to write to, "stdout" is a specially handled file.
   files = ["stdout", "/tmp/metrics.out"]
 
+  ## If this is defined, files will be rotated by the time.Duration specified
+  #rotate_max_age = "1m"
+
   ## Data format to output.
   ## Each data format has its own unique set of configuration options, read
   ## more about them here:

plugins/outputs/file/file.go

@@ -4,16 +4,19 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"time"
 
 	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/internal/rotate"
 	"github.com/influxdata/telegraf/plugins/outputs"
 	"github.com/influxdata/telegraf/plugins/serializers"
 )
 
 type File struct {
-	Files []string
+	Files        []string
+	RotateMaxAge string
 
-	writers []io.Writer
+	writer  io.Writer
 	closers []io.Closer
 
 	serializer serializers.Serializer
@@ -23,6 +26,9 @@ var sampleConfig = `
   ## Files to write to, "stdout" is a specially handled file.
   files = ["stdout", "/tmp/metrics.out"]
 
+  ## If this is defined, files will be rotated by the time.Duration specified
+  #rotate_max_age = "1m"
+
   ## Data format to output.
   ## Each data format has its own unique set of configuration options, read
   ## more about them here:
@@ -35,23 +41,38 @@ func (f *File) SetSerializer(serializer serializers.Serializer) {
 }
 
 func (f *File) Connect() error {
+	writers := []io.Writer{}
+
 	if len(f.Files) == 0 {
 		f.Files = []string{"stdout"}
 	}
 
 	for _, file := range f.Files {
 		if file == "stdout" {
-			f.writers = append(f.writers, os.Stdout)
+			writers = append(writers, os.Stdout)
 		} else {
-			of, err := os.OpenFile(file, os.O_CREATE|os.O_APPEND|os.O_WRONLY, os.ModeAppend|0644)
+			var of io.WriteCloser
+			var err error
+			if f.RotateMaxAge != "" {
+				maxAge, err := time.ParseDuration(f.RotateMaxAge)
+				if err != nil {
+					return err
+				}
+
+				// Only rotate by file age for now, keep no archives.
+				of, err = rotate.NewFileWriter(file, maxAge, 0, -1)
+			} else {
+				// Just open a normal file
+				of, err = rotate.NewFileWriter(file, 0, 0, -1)
+			}
 			if err != nil {
 				return err
 			}
-
-			f.writers = append(f.writers, of)
+			writers = append(writers, of)
 			f.closers = append(f.closers, of)
 		}
 	}
+	f.writer = io.MultiWriter(writers...)
 	return nil
 }
 
@@ -76,19 +97,19 @@ func (f *File) Description() string {
 
 func (f *File) Write(metrics []telegraf.Metric) error {
 	var writeErr error = nil
+
 	for _, metric := range metrics {
 		b, err := f.serializer.Serialize(metric)
 		if err != nil {
 			return fmt.Errorf("failed to serialize message: %s", err)
 		}
 
-		for _, writer := range f.writers {
-			_, err = writer.Write(b)
-			if err != nil && writer != os.Stdout {
-				writeErr = fmt.Errorf("E! failed to write message: %s, %s", b, err)
-			}
+		_, err = f.writer.Write(b)
+		if err != nil && f.writer != os.Stdout {
+			writeErr = fmt.Errorf("E! failed to write message: %s, %s", b, err)
 		}
 	}
+
 	return writeErr
 }