On 06/24/2015 11:36 AM, Oleg Fayans wrote:



On 06/24/2015 11:25 AM, Ludwig Krispenz wrote:
Oleg,

the topology plugin relies on existing connection between servers which remain in a topolgy. If you remove a central node in your topology you are asking for trouble. With Petr's patch it warns you that your topology will be disconnected, and if you insist we cannot guarantee anything.
Agree. I just wanted to try edge cases to see how one can break the system :)
should we completely prohibit this ? I don't know, I think you could also enforce an uninstall of vm175 with probably the same result. what you mean be calculating the remaining topology and send it to the remaining servers does not work, it would require to send a removal of a segment, which would be rejected.

The topology is broken, and I don't know how much we should invest in making this info consistent on all servers.

More interesting would be if we can heal this later by adding new segments.
Yes, here comes the biggest question raised from this case: obviously, when none of the nodes possess the correct topology information (including the one which deleted the central node), there is no way to fix it by adding segments connecting the nodes that became disconnected.
It shoul not need the full information, but it has to be able to reach one of the nodes to be connected. when the topology is broken, you loose to feature to be ably to apply a change on any node, eg in your case if you want to connect vm036 and vm056 an have removed vm175, you have to do it on vm056, vm036 or vm244. This should work, if not we have to fix it - unless we completely prevent disconnecting a topology
I still think that the recalculation of the resulting tree should be done at least on the node that performs the removal action. And when later some other node gets connected, it should understand somehow that it's topology information is outdated

Ludwig
On 06/24/2015 11:04 AM, Oleg Fayans wrote:
Hi everybody,

Current implementation of topology plugin (including patch 878 from Petr) allows the deletion of the central node in the star topology.
I had the following topology:

vm056      vm036
         \         /     |
         vm175     |
         /         \     |
vm127       vm244

I was able to remove node vm175 from node vm244:

[17:54:48]ofayans@vm-244:~]$ ipa-replica-manage del vm-175.idm.lab.eng.brq.redhat.com Topology after removal of vm-175.idm.lab.eng.brq.redhat.com will be disconnected: Server vm-036.idm.lab.eng.brq.redhat.com can't contact servers: vm-056.idm.lab.eng.brq.redhat.com, vm-127.idm.lab.eng.brq.redhat.com Server vm-056.idm.lab.eng.brq.redhat.com can't contact servers: vm-244.idm.lab.eng.brq.redhat.com, vm-036.idm.lab.eng.brq.redhat.com, vm-127.idm.lab.eng.brq.redhat.com Server vm-127.idm.lab.eng.brq.redhat.com can't contact servers: vm-244.idm.lab.eng.brq.redhat.com, vm-056.idm.lab.eng.brq.redhat.com, vm-036.idm.lab.eng.brq.redhat.com Server vm-244.idm.lab.eng.brq.redhat.com can't contact servers: vm-056.idm.lab.eng.brq.redhat.com, vm-127.idm.lab.eng.brq.redhat.com
Continue to delete? [no]: yes
Waiting for removal of replication agreements
unexpected error: limits exceeded for this query

I would expect this operation to delete 4 replication agreements on all nodes:
vm056 - vm175
vm127 - vm175
vm244 - vm175
vm036 - vm175

However an arbitrary set of replication agreements was deleted on each node leading to total infrastructure inconsistency:
===============================================================
vm056**thought the topology was as follows:
vm056      vm036
                   /     |
         vm175     |
         /         \     |
vm127       vm244
[10:28:55]ofayans@vm-056:~]$ ipa topologysegment-find realm
------------------
4 segments matched
------------------
  Segment name: 036-to-244
  Left node: vm-036.idm.lab.eng.brq.redhat.com
  Right node: vm-244.idm.lab.eng.brq.redhat.com
  Connectivity: both

Segment name: vm-036.idm.lab.eng.brq.redhat.com-to-vm-175.idm.lab.eng.brq.redhat.com
  Left node: vm-036.idm.lab.eng.brq.redhat.com
  Right node: vm-175.idm.lab.eng.brq.redhat.com
  Connectivity: both

Segment name: vm-127.idm.lab.eng.brq.redhat.com-to-vm-175.idm.lab.eng.brq.redhat.com
  Left node: vm-127.idm.lab.eng.brq.redhat.com
  Right node: vm-175.idm.lab.eng.brq.redhat.com
  Connectivity: both

Segment name: vm-175.idm.lab.eng.brq.redhat.com-to-vm-244.idm.lab.eng.brq.redhat.com
  Left node: vm-175.idm.lab.eng.brq.redhat.com
  Right node: vm-244.idm.lab.eng.brq.redhat.com
  Connectivity: both
----------------------------
Number of entries returned 4
----------------------------
===============================================================
both vm036**vm244 thought the topology was as follows:
vm056      vm036
         \               |
         vm175     |
         /               |
vm127       vm244

[10:26:23]ofayans@vm-036:~]$ ipa topologysegment-find
Suffix name: realm
------------------
3 segments matched
------------------
  Segment name: 036-to-244
  Left node: vm-036.idm.lab.eng.brq.redhat.com
  Right node: vm-244.idm.lab.eng.brq.redhat.com
  Connectivity: both

Segment name: vm-056.idm.lab.eng.brq.redhat.com-to-vm-175.idm.lab.eng.brq.redhat.com
  Left node: vm-056.idm.lab.eng.brq.redhat.com
  Right node: vm-175.idm.lab.eng.brq.redhat.com
  Connectivity: both

Segment name: vm-127.idm.lab.eng.brq.redhat.com-to-vm-175.idm.lab.eng.brq.redhat.com
  Left node: vm-127.idm.lab.eng.brq.redhat.com
  Right node: vm-175.idm.lab.eng.brq.redhat.com
  Connectivity: both
----------------------------
Number of entries returned 3
----------------------------

===============================================================
**vm127 thought the topology was as follows:
vm056      vm036
         \        /      |
         vm175     |
                  \      |
vm127       vm244

[10:31:08]ofayans@vm-127:~]$ ipa topologysegment-find realm
------------------
4 segments matched
------------------
  Segment name: 036-to-244
  Left node: vm-036.idm.lab.eng.brq.redhat.com
  Right node: vm-244.idm.lab.eng.brq.redhat.com
  Connectivity: both

Segment name: vm-036.idm.lab.eng.brq.redhat.com-to-vm-175.idm.lab.eng.brq.redhat.com
  Left node: vm-036.idm.lab.eng.brq.redhat.com
  Right node: vm-175.idm.lab.eng.brq.redhat.com
  Connectivity: both

Segment name: vm-056.idm.lab.eng.brq.redhat.com-to-vm-175.idm.lab.eng.brq.redhat.com
  Left node: vm-056.idm.lab.eng.brq.redhat.com
  Right node: vm-175.idm.lab.eng.brq.redhat.com
  Connectivity: both

Segment name: vm-175.idm.lab.eng.brq.redhat.com-to-vm-244.idm.lab.eng.brq.redhat.com
  Left node: vm-175.idm.lab.eng.brq.redhat.com
  Right node: vm-244.idm.lab.eng.brq.redhat.com
  Connectivity: both
----------------------------
Number of entries returned 4
----------------------------

If I, for example, add a segment connecting vm127 and vm244, these two nodes will not synchronize the topology info:

[10:51:03]ofayans@vm-127:~]$ ipa topologysegment-add realm 127-to-244 --leftnode=vm-127.idm.lab.eng.brq.redhat.com --rightnode=vm-244.idm.lab.eng.brq.redhat.com --direction=both
--------------------------
Added segment "127-to-244"
--------------------------
  Segment name: 127-to-244
  Left node: vm-127.idm.lab.eng.brq.redhat.com
  Right node: vm-244.idm.lab.eng.brq.redhat.com
  Connectivity: both
[10:53:33]ofayans@vm-127:~]$ ipa topologysegment-find realm
------------------
5 segments matched
------------------
  Segment name: 036-to-244
  Left node: vm-036.idm.lab.eng.brq.redhat.com
  Right node: vm-244.idm.lab.eng.brq.redhat.com
  Connectivity: both

  Segment name: 127-to-244
  Left node: vm-127.idm.lab.eng.brq.redhat.com
  Right node: vm-244.idm.lab.eng.brq.redhat.com
  Connectivity: both

Segment name: vm-036.idm.lab.eng.brq.redhat.com-to-vm-175.idm.lab.eng.brq.redhat.com
  Left node: vm-036.idm.lab.eng.brq.redhat.com
  Right node: vm-175.idm.lab.eng.brq.redhat.com
  Connectivity: both

Segment name: vm-056.idm.lab.eng.brq.redhat.com-to-vm-175.idm.lab.eng.brq.redhat.com
  Left node: vm-056.idm.lab.eng.brq.redhat.com
  Right node: vm-175.idm.lab.eng.brq.redhat.com
  Connectivity: both

Segment name: vm-175.idm.lab.eng.brq.redhat.com-to-vm-244.idm.lab.eng.brq.redhat.com
  Left node: vm-175.idm.lab.eng.brq.redhat.com
  Right node: vm-244.idm.lab.eng.brq.redhat.com
  Connectivity: both
----------------------------
Number of entries returned 5
----------------------------
[10:54:02]ofayans@vm-127:~]$

=============================================================

[10:49:38]ofayans@vm-244:~]$ ipa topologysegment-find realm
------------------
3 segments matched
------------------
  Segment name: 036-to-244
  Left node: vm-036.idm.lab.eng.brq.redhat.com
  Right node: vm-244.idm.lab.eng.brq.redhat.com
  Connectivity: both

  Segment name: 127-to-244
  Left node: vm-127.idm.lab.eng.brq.redhat.com
  Right node: vm-244.idm.lab.eng.brq.redhat.com
  Connectivity: both

Segment name: vm-056.idm.lab.eng.brq.redhat.com-to-vm-175.idm.lab.eng.brq.redhat.com
  Left node: vm-056.idm.lab.eng.brq.redhat.com
  Right node: vm-175.idm.lab.eng.brq.redhat.com
  Connectivity: both
----------------------------
Number of entries returned 3
----------------------------
[10:56:34]ofayans@vm-244:~]$

Conclusion:
We either should completely prohibit the removal of the middle nodes (I mean, nodes that hide another active nodes), or at the removal stage first recalculate the resulting topology and send it to all nodes before actual removal.
--
Oleg Fayans
Quality Engineer
FreeIPA team
RedHat.






--
Oleg Fayans
Quality Engineer
FreeIPA team
RedHat.



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