Adds Memcached dependencies doc

Since Memcached is not used by the majority of deployments, its
dependencies are not included by default in the requirements.txt
file. This patch adds the documentation about the need to
manually install those dependencies.

Change-Id: Ic6252b1e00168fa2236f8a892212084da6cfdd64
Closes-Bug: 1392264

1 files changed, 12 insertions, 2 deletions

diff --git a/doc/source/middlewarearchitecture.rst b/doc/source/middlewarearchitecture.rst
index be2c690..e93bc4b 100644
--- a/doc/source/middlewarearchitecture.rst
+++ b/doc/source/middlewarearchitecture.rst
@@ -365,6 +365,18 @@ provide the ``cache`` option.
 * ``cache``: (optional) if defined, the environment key where the Swift
   MemcacheRing object is stored.
 
+Memcached dependencies
+======================
+
+In order to use `memcached`_ it is necessary to install the `python-memcached`_
+library. If data stored in `memcached`_ will need to be encrypted it is also
+necessary to install the `pycrypto`_ library. These libs are not listed in
+the requirements.txt file.
+
+.. _`memcached`: http://memcached.org/
+.. _`python-memcached`: https://pypi.python.org/pypi/python-memcached
+.. _`pycrypto`: https://pypi.python.org/pypi/pycrypto
+
 Memcached and System Time
 =========================
 
@@ -374,8 +386,6 @@ time in determining whether a key has expired, whereas Keystone sets
 key expiry in UTC.  The timezone used by Keystone and memcached must
 match if key expiry is to behave as expected.
 
-.. _`memcached`: http://memcached.org/
-
 Memcache Protection
 ===================