Any even number that is greater than half of the configured number of nodes is fine.
The only *really* bad even number of servers is 0. On Thu, Mar 8, 2012 at 4:24 PM, Ted Dunning <ted.dunn...@gmail.com> wrote: > It won't be any different than a temporary state when one of 3 or 5 nodes > is down. > > > On Thu, Mar 8, 2012 at 4:10 PM, Jordan Zimmerman > <jzimmer...@netflix.com>wrote: > >> AlsoŠ >> >> I thought that ZK ensembles need to be odd in number. How would ZK handle >> a temporary state where there is an even number? >> >> -JZ >> >> On 3/8/12 3:39 PM, "Alexander Shraer" <shra...@yahoo-inc.com> wrote: >> >> >I don't think there is a problem if you do it as you say, or even if you >> >just change the config files of all servers at once and restart them, >> >because a majority of the new config >> >necessarily intersects with a majority of the old one, so a server who >> >has the latest state will be elected leader. >> > >> >Alex >> > >> >> -----Original Message----- >> >> From: Jordan Zimmerman [mailto:jzimmer...@netflix.com] >> >> Sent: Thursday, March 08, 2012 3:31 PM >> >> To: user@zookeeper.apache.org >> >> Subject: Rolling upgrades >> >> >> >> I've been reading the archives regarding rolling upgrades. Here's the >> >> scenario, given a stable ensemble: >> >> >> >> ZK1 <-> ZK2 <-> ZK3 >> >> >> >> In the above, the zoo.cfg for each server looks like this (pseudo): >> >> server.1=ZK1 >> >> server.2=ZK2 >> >> server.3=ZK3 >> >> >> >> I want to add a new server, ZK4. If I understand this correctly, I'd >> >> bring up ZK4 with this config: >> >> server.1=ZK1 >> >> server.2=ZK2 >> >> server.3=ZK3 >> >> server.4=ZK4 >> >> >> >> At this point, though, the configs don't match in the ensemble. How do >> >> the ZK instances handle this? >> >> >> >> Continuing... >> >> >> >> Once ZK4 is up, ZK1 would get the new config and get restarted. Once >> >> ZK1 is up, ZK2 gets new config, etc. >> >> >> >> At each point of config change, the cluster is in a confused state >> >> about the config. Is there code in ZK to handle this? >> >> >> >> -JZ >> > >> > >> >> >
