ovsdb: Introduce experimental support for clustered databases.

This commit adds support for OVSDB clustering via Raft.  Please read
ovsdb(7) for information on how to set up a clustered database.  It is
simple and boils down to running "ovsdb-tool create-cluster" on one server
and "ovsdb-tool join-cluster" on each of the others and then starting
ovsdb-server in the usual way on all of them.

One you have a clustered database, you configure ovn-controller and
ovn-northd to use it by pointing them to all of the servers, e.g. where
previously you might have said "tcp:1.2.3.4" was the database server,
now you say that it is "tcp:1.2.3.4,tcp:5.6.7.8,tcp:9.10.11.12".

This also adds support for database clustering to ovs-sandbox.

Acked-by: Justin Pettit <jpettit@ovn.org>
Tested-by: aginwala <aginwala@asu.edu>
Signed-off-by: Ben Pfaff <blp@ovn.org>

1 files changed, 63 insertions, 0 deletions

diff --git a/ovsdb/TODO.rst b/ovsdb/TODO.rst
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+..
+      Licensed under the Apache License, Version 2.0 (the "License"); you may
+      not use this file except in compliance with the License. You may obtain
+      a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+      Unless required by applicable law or agreed to in writing, software
+      distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+      WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+      License for the specific language governing permissions and limitations
+      under the License.
+
+      Convention for heading levels in Open vSwitch documentation:
+
+      =======  Heading 0 (reserved for the title in a document)
+      -------  Heading 1
+      ~~~~~~~  Heading 2
+      +++++++  Heading 3
+      '''''''  Heading 4
+
+      Avoid deeper levels because they do not render well.
+
+===========================
+OVSDB Clustering To-do List
+===========================
+
+* Ephemeral columns.
+
+* Unit test snapshotting.
+
+* Locks.
+
+* Investigate 100% CPU for long-running triggers
+
+* Tons of unit tests.
+
+* Increase exponential backoff cap.  Introduce randomization.
+
+* Include index with monitor update?
+
+* Back off when transaction fails to commit?  Definitely back off until
+  the eid changes for prereq failures
+
+* Testing with replication.
+
+* Handling bad transactions in read_db().  (Kill the database?)
+
+* Documentation:
+
+  * ACID (and CAP?) explanation.
+
+  * Upgrading OVN to a clustered database
+
+  * Installing OVN with a clustered database
+
+  * Overall diagram explaining the cluster and ovsdb protocol pieces
+
+* Future work:
+
+  * File format with diff support.
+
+  * Future work: DNS or directory support