We have just done an upgrade of ZK to 3.3.0. Previous to this, ZK has been
up for about a year with no problems.
On two nodes, we killed the previous instance and started the 3.3.0
instance. The first node was a follower and the second a leader.
All went according to plan and no clients seemed to notice anything. The
stat command showed connections moving around as expected and all other
indicators were normal.
When we did the third node, we saw this in the log:
2010-04-20 14:07:49,010 - FATAL [QuorumPeer:/0.0.0.0:2181:follo...@71] -
Leader epoch 18 is less than our epoch 19
The third node refused all connections.
We brought down the third node, wiped away its snapshot, restarted and it
joined without complaint. Note that the third node
was originally a follower and had never been a leader during the upgrade
Does anybody know why this happened?
We are fully upgraded and there was no interruption to normal service, but
this seems strange.