[Freeipa-devel] Topology: Central node removal in star topology
Ludwig Krispenz
lkrispen at redhat.com
Wed Jun 24 10:28:48 UTC 2015
On 06/24/2015 12:02 PM, Oleg Fayans wrote:
>
>
> On 06/24/2015 11:47 AM, Ludwig Krispenz wrote:
>>
>> 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
> Well, this is exactly the problem here: all replicas should contain
> precise copies of all the info: accounts, hosts, sudorules, etc,
> including topology information. However, if in this case I manually
> connect disconnected node at vm127 (or vm056, does not matter) it
> results in topology information inconsistency across the infrastructure:
> This would be the topology from the point of view of vm127:
did you add teh connection on vm127 or on vm244 ? sorry, but in these
situations to understand what's going on, it can matter.
to me it looks like you did it on vm127, so its there, it got replicated
to vm244, but replicationback does not work and so the deletion of teh
segs to vm175, which should still be in the changelogs of 036 and 244,
don#t get to 127. Do you have something in the error logs of 244 ?
>
> vm056 vm036
> \ / |
> vm175 |
> \ |
> vm127 vm244
>
> And this - from the point of view of vm244 and vm036
>
> vm056 vm036
> \ |
> vm175 |
> |
> vm127 ----- vm244
>>> 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 at 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 at 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 at 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 at 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 at 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 at 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 at vm-127:~]$
>>>>>
>>>>> =============================================================
>>>>>
>>>>> [10:49:38]ofayans at 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 at 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.
>>>
>>>
>>
>>
>>
>
> --
> Oleg Fayans
> Quality Engineer
> FreeIPA team
> RedHat.
>
>
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