[master] 4e0da85 Blurb about UDS in "What's New in 6.0".

Geoff Simmons geoff at uplex.de
Wed Mar 14 11:38:09 UTC 2018

commit 4e0da85ee43c579a21fbfb683520a1afb472525f
Author: Geoff Simmons <geoff at uplex.de>
Date:   Wed Mar 14 12:37:05 2018 +0100

    Blurb about UDS in "What's New in 6.0".

diff --git a/doc/sphinx/whats-new/changes-6.0.rst b/doc/sphinx/whats-new/changes-6.0.rst
index 73ea543..9b860fe 100644
--- a/doc/sphinx/whats-new/changes-6.0.rst
+++ b/doc/sphinx/whats-new/changes-6.0.rst
@@ -22,10 +22,57 @@ XXX subsubhead 1.2
 XXX: ...
-XXX subhead 2
+.. _whatsnew_new_uds:
-XXX ...
+Unix domain sockets as listen and backend addresses
+If you are using VCL 4.1, the ``varnishd -a`` command-line argument
+allows you to specify Unix domain sockets as listener addresses
+(beginning with ``/``, see varnishd :ref:`ref-varnishd-options`)::
+  varnishd -a /path/to/listen.sock,PROXY,user=vcache,group=varnish,mode=660
+The ``user``, ``group`` and ``mode`` sub-arguments set the permissions
+of the newly created socket file.
+A backend declaration in VCL 4.1 may now include the ``.path`` field
+(instead of ``.host``) for the absolute path of a Unix domain socket
+to which Varnish connects::
+  backend uds {
+  	.path = "/path/to/backend.sock";
+  }
+This of course can only be used to communicate with other processes on
+the same host, if they also support socket file addresses. Until now,
+connections with other process co-located with Varnish were only
+possible over locally available IP addresses, such as loopback. Unix sockets
+may have some advantages for such a configuration:
+* Network traffic over Unix sockets does not have the overhead of the
+  TCP stack. You may see a significant improvement in throughput
+  compared to using the loopback address.
+* The file permission system can be used to impose restrictions on the
+  processes that can connect to Varnish, and the processes to which
+  Varnish can connect.
+* Using paths as addresses may be easier to configure than searching
+  for open port numbers on loopback, especially for automated
+  configurations.
+The obvious use cases are SSL offloaders that decrypt traffic from the
+network and pass requests on to Varnish, and SSL "onloaders" that
+encrypt backend traffic from Varnish and forward requests over
+untrusted networks. But this should be useful for any configuration in
+which Varnish talks to processes on the same host.
+The distribution has a new :ref:`VMOD unix <vmod_unix(3)>` that you
+may be able to use in VCL to get information about the credentials of
+a process (user and group of the process owner) that is connected to a
+Varnish listener over a Unix socket. This is not supported on every
+platform, so check the VMOD docs to see if it will work for you.
 XXX subsubhead 2.1

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