enable diskless replication configuration

README.md

@@ -343,6 +343,8 @@ Available options and their defaults
 'masterauth'              => nil,
 'slaveservestaledata'     => 'yes',
 'slavereadonly'           => 'yes',
+'repldisklesssync'        => 'no', # Requires redis 2.8.18+
+'repldisklesssyncdelay'   => '5', # Requires redis 2.8.18+
 'replpingslaveperiod'     => '10',
 'repltimeout'             => '60',
 'repldisabletcpnodelay    => 'no',

attributes/default.rb

@@ -114,6 +114,8 @@
   'masterauth'              => nil,
   'slaveservestaledata'     => 'yes',
   'slavereadonly'           => 'yes',
+  'repldisklesssync'        => 'no',
+  'repldisklesssyncdelay'   => '5',
   'replpingslaveperiod'     => '10',
   'repltimeout'             => '60',
   'repldisabletcpnodelay'   => 'no',

providers/configure.rb

@@ -294,7 +294,9 @@ def configure
           clusternodetimeout:         current['clusternodetimeout'],
           includes:                   current['includes'],
           minslavestowrite:           current['minslavestowrite'],
-          minslavesmaxlag:            current['minslavesmaxlag']
+          minslavesmaxlag:            current['minslavesmaxlag'],
+          repldisklesssync:           current['repldisklesssync'],
+          repldisklesssyncdelay:      current['repldisklesssyncdelay']
         )
         not_if { ::File.exist?("#{current['configdir']}/#{server_name}.conf.breadcrumb") }
       end

templates/default/redis.conf.erb

@@ -250,6 +250,71 @@ dir <%=@datadir%>
 #    but to INFO and SLAVEOF.
 #
 slave-serve-stale-data <%=@slaveservestaledata%>
+<% if @version[:major].to_i == 2 && @version[:minor].to_i >= 6 || @version[:major].to_i >= 3 -%>
+<% ######## Redis 2.6 and higher ######## -%>
+
+# You can configure a slave instance to accept writes or not. Writing against
+# a slave instance may be useful to store some ephemeral data (because data
+# written on a slave will be easily deleted after resync with the master) but
+# may also cause problems if clients are writing to it because of a
+# misconfiguration.
+#
+# Since Redis 2.6 by default slaves are read-only.
+#
+# Note: read only slaves are not designed to be exposed to untrusted clients
+# on the internet. It's just a protection layer against misuse of the instance.
+# Still a read only slave exports by default all the administrative commands
+# such as CONFIG, DEBUG, and so forth. To a limited extent you can improve
+# security of read only slaves using 'rename-command' to shadow all the
+# administrative / dangerous commands.
+slave-read-only <%=@slavereadonly%>
+<% end %>
+
+<% if (@version[:major].to_i == 2 && @version[:minor].to_i == 8 && @version[:tiny].to_i >= 18) or (@version[:major].to_i == 2 && @version[:minor].to_i >= 9) or @version[:major].to_i >= 3 -%>
+<% ######## Redis 2.8.18 and higher ######## -%>
+# Replication SYNC strategy: disk or socket.
+#
+# -------------------------------------------------------
+# WARNING: DISKLESS REPLICATION IS EXPERIMENTAL CURRENTLY
+# -------------------------------------------------------
+#
+# New slaves and reconnecting slaves that are not able to continue the replication
+# process just receiving differences, need to do what is called a "full
+# synchronization". An RDB file is transmitted from the master to the slaves.
+# The transmission can happen in two different ways:
+#
+# 1) Disk-backed: The Redis master creates a new process that writes the RDB
+#                 file on disk. Later the file is transferred by the parent
+#                 process to the slaves incrementally.
+# 2) Diskless: The Redis master creates a new process that directly writes the
+#              RDB file to slave sockets, without touching the disk at all.
+#
+# With disk-backed replication, while the RDB file is generated, more slaves
+# can be queued and served with the RDB file as soon as the current child producing
+# the RDB file finishes its work. With diskless replication instead once
+# the transfer starts, new slaves arriving will be queued and a new transfer
+# will start when the current one terminates.
+#
+# When diskless replication is used, the master waits a configurable amount of
+# time (in seconds) before starting the transfer in the hope that multiple slaves
+# will arrive and the transfer can be parallelized.
+#
+# With slow disks and fast (large bandwidth) networks, diskless replication
+# works better.
+repl-diskless-sync <%=@repldisklesssync%>
+
+# When diskless replication is enabled, it is possible to configure the delay
+# the server waits in order to spawn the child that transfers the RDB via socket
+# to the slaves.
+#
+# This is important since once the transfer starts, it is not possible to serve
+# new slaves arriving, that will be queued for the next RDB transfer, so the server
+# waits a delay in order to let more slaves arrive.
+#
+# The delay is specified in seconds, and by default is 5 seconds. To disable
+# it entirely just set it to 0 seconds and the transfer will start ASAP.
+repl-diskless-sync-delay <%=@repldisklesssyncdelay%>
+<% end %>
 
 <% if @version[:major].to_i == 2 && @version[:minor].to_i >= 6 || @version[:major].to_i == 3 %>
 # You can configure a slave instance to accept writes or not. Writing against