2.1 design: propose redistribute config changes

This patch proposes a mini-design to improve redistribute-config and
integrate it better with other logical units.

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

doc/design-2.1.rst

@@ -40,6 +40,47 @@ Core changes
 Feature changes
 ---------------
 
+Redistribute Config
+~~~~~~~~~~~~~~~~~~~
+
+Current State and shortcomings
+++++++++++++++++++++++++++++++
+Currently LURedistributeConfig triggers a copy of the updated configuration
+file to all master candidates and of the ssconf files to all nodes. There are
+other files which are maintained manually but which are important to keep in
+sync. These are:
+
+- rapi SSL key certificate file (rapi.pem) (on master candidates)
+- rapi user/password file rapi_users (on master candidates)
+
+Furthermore there are some files which are hypervisor specific but we may want
+to keep in sync:
+
+- the xen-hvm hypervisor uses one shared file for all vnc passwords, and copies
+  the file once, during node add. This design is subject to revision to be able
+  to have different passwords for different groups of instances via the use of
+  hypervisor parameters, and to allow xen-hvm and kvm to use an equal system to
+  provide password-protected vnc sessions. In general, though, it would be
+  useful if the vnc password files were copied as well, to avoid unwanted vnc
+  password changes on instance failover/migrate.
+
+Optionally the admin may want to also ship files such as the global xend.conf
+file, and the network scripts to all nodes.
+
+Proposed changes
+++++++++++++++++
+
+RedistributeConfig will be changed to copy also the rapi files, and to call
+every enabled hypervisor asking for a list of additional files to copy. We also
+may want to add a global list of files on the cluster object, which will be
+propagated as well, or a hook to calculate them. If we implement this feature
+there should be a way to specify whether a file must be shipped to all nodes or
+just master candidates.
+
+This code will be also shared (via tasklets or by other means, if tasklets are
+not ready for 2.1) with the AddNode and SetNodeParams LUs (so that the relevant
+files will be automatically shipped to new master candidates as they are set).
+
 External interface changes
 --------------------------