Removed node, jumps back into the cluster

[Fredrik <fr...@sitevision.se>]

I've tested a scenario where I wanted to reuse a removed node in a new 
cluster with same IP, maybe not very common but anyway, found some 
strange behaviour in Gossiper.

Here is what I think/see happening:
- Cassandra 1.1. Three node cluster A, B and C.
- Shutdown node C and remove token for node C.
- Everything looks ok in logs, reporting that node C is removed etc..
- Node A and B still sends Gossip digest about the removed node, but I 
guess that's ok since they know about it (Gossiper.endpointStateMap).
- Node C has status removed when checking in JMX console.
- Checked in LocationInfo that Ring only contains token/IP for node A and B.
- Removed system/data tables for C.
- Changed seed on C to point to itself.
- Startup node C, node C only gossips itself and node A and B doesn't 
recognize that node C is running, which is correct.
- Restart e.g. node A. Now node A will loose all gossip information 
(Gossiper.endpointStateMap) about node C. Node A will request 
information from LocationInfo and ask node B
   about endpoint states. Node A will receive information from node B 
about node C, this will trigger Gossiper.handleMajorStateChange and node 
C will be first marked as unreachable
   because it's in dead state (removed), node A will try to Gossip 
(unreachable endpoints) to node C, which will reply that it's up and 
node C becomes incorporated into the "old" cluster again.

Is this a a bug or is it a requirement that if you take a node out of 
the cluster you must change IP on the removed node if you want to use it 
in another cluster?
Please enlight me.

Regards
/Fredrik

Re: Removed node, jumps back into the cluster

[Fredrik Stigbäck <fr...@sitevision.se>]

Wrong assumption of me. I found the answer in
GossipDigestSynVerbHandler. I forgot to change the cluster name of the
new cluster.

/Fredrik

2012/9/11 Fredrik <fr...@sitevision.se>:
> I've tested a scenario where I wanted to reuse a removed node in a new
> cluster with same IP, maybe not very common but anyway, found some strange
> behaviour in Gossiper.
>
> Here is what I think/see happening:
> - Cassandra 1.1. Three node cluster A, B and C.
> - Shutdown node C and remove token for node C.
> - Everything looks ok in logs, reporting that node C is removed etc..
> - Node A and B still sends Gossip digest about the removed node, but I guess
> that's ok since they know about it (Gossiper.endpointStateMap).
> - Node C has status removed when checking in JMX console.
> - Checked in LocationInfo that Ring only contains token/IP for node A and B.
> - Removed system/data tables for C.
> - Changed seed on C to point to itself.
> - Startup node C, node C only gossips itself and node A and B doesn't
> recognize that node C is running, which is correct.
> - Restart e.g. node A. Now node A will loose all gossip information
> (Gossiper.endpointStateMap) about node C. Node A will request information
> from LocationInfo and ask node B
>   about endpoint states. Node A will receive information from node B about
> node C, this will trigger Gossiper.handleMajorStateChange and node C will be
> first marked as unreachable
>   because it's in dead state (removed), node A will try to Gossip
> (unreachable endpoints) to node C, which will reply that it's up and node C
> becomes incorporated into the "old" cluster again.
>
> Is this a a bug or is it a requirement that if you take a node out of the
> cluster you must change IP on the removed node if you want to use it in
> another cluster?
> Please enlight me.
>
> Regards
> /Fredrik
>
>
>



-- 
Fredrik Larsson Stigbäck
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