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From Steve Boyle <>
Subject Leader Latch question
Date Wed, 17 Aug 2016 17:43:35 GMT
I'm using the Leader Latch recipe.  I can successfully bring up two instances of my app and
have one become 'active' and one become 'standby'.  Most everything works as expected.  We
had an issue, in production, when adding a zookeeper to our existing quorum, both instances
of the app became 'active'.  Unfortunately, the log files rolled over before we could check
for exceptions.  I've been trying to reproduce this issue in a test environment.  In my test
environment, I have two instances of my app configured to use a single zookeeper - this zookeeper
is part of a 5 node quorum and is not currently the leader.  I can trigger both instances
of the app to become 'active' if I use zkCli and manually delete the latch path from the single
zookeeper to which my apps are connected.  When I manually delete the latch path, I can see
via debug logging that the instance that was previously 'standby' gets a notification from
zookeeper "Got WatchedEvent state:SyncConnected type:NodeDeleted".  However, the instance
that had already been active gets no notification at all.  Is it expected that manually removing
the latch path would only generate notifications to some instances of my app?

Steve Boyle

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