Adding design doc for cluster merger

Signed-off-by: René Nussbaumer <rn@google.com>
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>
(applied slightly modified patch)

diff --git a/Makefile.am b/Makefile.am
index 10650fc..7d585ef 100644 (file)
--- a/Makefile.am
+++ b/Makefile.am
@@ -145,6 +145,7 @@ docrst = \
        doc/design-2.0.rst \
        doc/design-2.1.rst \
        doc/design-2.2.rst \
+       doc/design-cluster-merger.rst \
        doc/devnotes.rst \
        doc/glossary.rst \
        doc/hooks.rst \

diff --git a/doc/design-cluster-merger.rst b/doc/design-cluster-merger.rst
new file mode 100644 (file)
index 0000000..2ab744e
--- /dev/null
+++ b/doc/design-cluster-merger.rst
@@ -0,0 +1,127 @@
+=====================
+Ganeti Cluster Merger
+=====================
+
+Current situation
+=================
+
+Currently there's no easy way to merge two or more clusters together.
+But in order to optimize resources this is a needed missing piece. The
+goal of this design doc is to come up with a easy to use solution which
+allows you to merge two or more cluster together.
+
+Initial contact
+===============
+
+As the design of Ganeti is based on an autonomous system, Ganeti by
+itself has no way to reach nodes outside of its cluster. To overcome
+this situation we're required to prepare the cluster before we can go
+ahead with the actual merge: We've to replace at least the ssh keys on
+the affected nodes before we can do any operation within ``gnt-``
+commands.
+
+To make this a automated process we'll ask the user to provide us with
+the root password of every cluster we've to merge. We use the password
+to grab the current ``id_dsa`` key and then rely on that ssh key for any
+further communication to be made until the cluster is fully merged.
+
+Cluster merge
+=============
+
+After initial contact we do the cluster merge:
+
+1. Grab the list of nodes
+2. On all nodes add our own ``id_dsa.pub`` key to ``authorized_keys``
+3. Stop all instances running on the merging cluster
+4. Disable ``ganeti-watcher`` as it tries to restart Ganeti daemons
+5. Stop all Ganeti daemons on all merging nodes
+6. Grab the ``config.data`` from the master of the merging cluster
+7. Stop local ``ganeti-masterd``
+8. Merge the config:
+
+   1. Open our own cluster ``config.data``
+   2. Open cluster ``config.data`` of the merging cluster
+   3. Grab all nodes of the merging cluster
+   4. Set ``master_candidate`` to false on all merging nodes
+   5. Add the nodes to our own cluster ``config.data``
+   6. Grab all the instances on the merging cluster
+   7. Adjust the port if the instance has drbd layout:
+
+      1. In ``logical_id`` (index 2)
+      2. In ``physical_id`` (index 1 and 3)
+
+   8. Add the instances to our own cluster ``config.data``
+
+9. Start ``ganeti-masterd`` with ``--no-voting`` ``--yes-do-it``
+10. ``gnt-node add --readd`` on all merging nodes
+11. ``gnt-cluster redist-conf``
+12. Restart ``ganeti-masterd`` normally
+13. Enable ``ganeti-watcher`` again
+14. Start all merging instances again
+
+Rollback
+========
+
+Until we actually (re)add any nodes we can abort and rollback the merge
+at any point. After merging the config, though, we've to get the backup
+copy of ``config.data`` (from another master candidate node). And for
+security reasons it's a good idea to undo ``id_dsa.pub`` distribution by
+going on every affected node and remove the ``id_dsa.pub`` key again.
+Also we've to keep in mind, that we've to start the Ganeti daemons and
+starting up the instances again.
+
+Verification
+============
+
+Last but not least we should verify that the merge was successful.
+Therefore we run ``gnt-cluster verify``, which ensures that the cluster
+overall is in a healthy state. Additional it's also possible to compare
+the list of instances/nodes with a list made prior to the upgrade to
+make sure we didn't lose any data/instance/node.
+
+Appendix
+========
+
+cluster-merge.py
+----------------
+
+Used to merge the cluster config. This is a POC and might differ from
+actual production code.
+
+::
+
+  #!/usr/bin/python
+
+  import sys
+  from ganeti import config
+  from ganeti import constants
+
+  c_mine = config.ConfigWriter(offline=True)
+  c_other = config.ConfigWriter(sys.argv[1])
+
+  fake_id = 0
+  for node in c_other.GetNodeList():
+    node_info = c_other.GetNodeInfo(node)
+    node_info.master_candidate = False
+    c_mine.AddNode(node_info, str(fake_id))
+    fake_id += 1
+
+  for instance in c_other.GetInstanceList():
+    instance_info = c_other.GetInstanceInfo(instance)
+    for dsk in instance_info.disks:
+      if dsk.dev_type in constants.LDS_DRBD:
+         port = c_mine.AllocatePort()
+         logical_id = list(dsk.logical_id)
+         logical_id[2] = port
+         dsk.logical_id = tuple(logical_id)
+         physical_id = list(dsk.physical_id)
+         physical_id[1] = physical_id[3] = port
+         dsk.physical_id = tuple(physical_id)
+    c_mine.AddInstance(instance_info, str(fake_id))
+    fake_id += 1
+
+.. vim: set textwidth=72 :
+.. Local Variables:
+.. mode: rst
+.. fill-column: 72
+.. End:

diff --git a/doc/index.rst b/doc/index.rst
index 0d1e1c0..15b5054 100644 (file)
--- a/doc/index.rst
+++ b/doc/index.rst
@@ -17,6 +17,7 @@ Contents:
    design-2.0.rst
    design-2.1.rst
    design-2.2.rst
+   design-cluster-merger.rst
    locking.rst
    hooks.rst
    iallocator.rst