Add logrotate example

Example template that uses a comma-separated value of log files
stored in a container environment variable named "LOG_FILES."  The
value is split on the comma character and then each log file is
listed in the logrotate config file through the hosts file system.

Each container's docker JSON log file is also listed for rotation
to prevent it from growin indefinitely.

Author: jwilder

template.go

@@ -7,6 +7,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"strings"
 	"text/template"
 )
 
@@ -33,6 +34,7 @@ func generateFile(config Config, containers []*RuntimeContainer) bool {
 	tmpl, err := template.New(filepath.Base(templatePath)).Funcs(template.FuncMap{
 		"contains": contains,
 		"groupBy":  groupBy,
+		"split":    strings.Split,
 	}).ParseFiles(templatePath)
 	if err != nil {
 		panic(err)

templates/logrotate.tmpl

@@ -0,0 +1,27 @@
+{{ range $index, $value := $ }}
+{{ $logs := $value.Env.LOG_FILES }}
+{{ if $logs }}
+{{ range $index, $logfile := split $logs "," }}
+/var/lib/docker/containers/{{ $value.ID }}/root{{ $logfile }}{{ end}}
+{
+    daily
+    missingok
+    rotate 52
+    compress
+    delaycompress
+    notifempty
+    create 644 root root
+}
+{{ end }}
+/var/lib/docker/containers/{{ $value.ID }}/{{ $value.ID }}-json.log
+{
+    daily
+    missingok
+    rotate 7
+    compress
+    delaycompress
+    notifempty
+    create 644 root root
+}
+{{ end }}
+