introduce optional rsyncable flag

doc/raketasks/backup_restore.md

@@ -205,6 +205,13 @@ sudo gitlab-rake gitlab:backup:create BACKUP=dump
 
 The resulting file will then be `dump_gitlab_backup.tar`. This is useful for systems that make use of rsync and incremental backups, and will result in considerably faster transfer speeds.
 
+### Rsyncable
+
+To make sure the generated archive is intelligently transferable by rsync, the `GZIP_RSYNCABLE=yes` option can be set. This will set the `--rsyncable` option to `gzip`. This is only useful in combination with setting [the Backup filename option](#backup-filename). Note that this option in `gzip` is not guaranteed to be available on all distributions.
+
+```sh
+sudo gitlab-rake gitlab:backup:create BACKUP=dump GZIP_RSYNCABLE=yes
+```
 
 ### Excluding specific directories from the backup
 

lib/backup/database.rb

@@ -4,6 +4,7 @@ require 'yaml'
 
 module Backup
   class Database
+    include Backup::Helper
     attr_reader :progress
     attr_reader :config, :db_file_name
 
@@ -17,7 +18,7 @@ module Backup
       FileUtils.mkdir_p(File.dirname(db_file_name))
       FileUtils.rm_f(db_file_name)
       compress_rd, compress_wr = IO.pipe
-      compress_pid = spawn(*%w(gzip --rsyncable -1 -c), in: compress_rd, out: [db_file_name, 'w', 0600])
+      compress_pid = spawn(gzip_cmd, in: compress_rd, out: [db_file_name, 'w', 0600])
       compress_rd.close
 
       dump_pid =

lib/backup/files.rb

@@ -31,10 +31,10 @@ module Backup
           raise Backup::Error, 'Backup failed'
         end
 
-        run_pipeline!([%W(#{tar} --exclude=lost+found -C #{@backup_files_dir} -cf - .), %w(gzip --rsyncable -c -1)], out: [backup_tarball, 'w', 0600])
+        run_pipeline!([%W(#{tar} --exclude=lost+found -C #{@backup_files_dir} -cf - .), gzip_cmd], out: [backup_tarball, 'w', 0600])
         FileUtils.rm_rf(@backup_files_dir)
       else
-        run_pipeline!([%W(#{tar} --exclude=lost+found -C #{app_files_dir} -cf - .), %w(gzip --rsyncable -c -1)], out: [backup_tarball, 'w', 0600])
+        run_pipeline!([%W(#{tar} --exclude=lost+found -C #{app_files_dir} -cf - .), gzip_cmd], out: [backup_tarball, 'w', 0600])
       end
     end
 

lib/backup/helper.rb

@@ -29,5 +29,14 @@ module Backup
       EOS
       raise message
     end
+
+    def gzip_cmd
+      @gzip_cmd ||= if ENV['GZIP_RSYNCABLE'] = 'yes'
+                      "gzip --rsyncable -c -1"
+                    else
+                      "gzip -c -1"
+                    end
+    end
+
   end
 end