Thanks to all of you guys. I will try it out. By any chance does anyone know when would the final/stable version of 3.5.0 be available. Because I can see it's in 3.5.0-alpha.
Thanks, Srini -----Original Message----- From: Rakesh [mailto:[email protected]] Sent: Tuesday, July 14, 2015 10:12 AM To: [email protected]; Srinivasan Veerapandian Cc: Alexander Shraer Subject: Re: ZooKeeper ensemble. Size and Impact ? Thank you Alex for the info. Hi Srini, I think Observer would be fine for your case. Probably you can try it out. -Rakesh On 13 Jul 2015 21:41, Alexander Shraer <[email protected]> wrote: > > In 3.4 releases you can't connect an observer to a standalone > zookeeper server, but in 3.5.0 if you set standaloneEnabled=false your > server will run in a "distributed" > mode even if its the only one and > you'll be able to have observers or reconfigure adding more servers > later if needed. > > On Mon, Jul 13, 2015 at 5:34 AM, Rakesh R <[email protected]> wrote: > > > > > >>>>> Is it so that only ensemble would be down but other functions > > >>>>> would > > be up and running like data-sync ... ? > > Say, if a ZooKeeper server lost connection with the quorum. It will > > shutdown all the services and try to join the quorum by starting > > internal election algo. There is a special type of "read-only" > > server, on connection lost, it will automatically transition to r-o > > mode and serve only the requests from r-o client. Please visit > > http://zookeeper.apache.org/doc/trunk/zookeeperAdmin.html for more > > details about r-o feature. > > > > >>>>> My need to run only 2 ZKS as I'm ok with have +1 copy of the data. > > Is there a way to run a dummy ZKS in any of the instance ? > > There is a typical 'Observer' server mode which will act as an > > observer and only syncup data with the Leader server, but I'm not > > really sure whether it will work along with Standalone server. I > > haven't tried yet, probably you can do a try > > http://zookeeper.apache.org/doc/r3.5.0-alpha/zookeeperObservers.html > > > > To begin with, you can run both as Participant and later if you want > > to change servers you can use reconfig feature, > > http://zookeeper.apache.org/doc/trunk/zookeeperReconfig.html > > In 1+1 deployment, tolerated failure is 0 and you should ensure both > > servers are up & running for the availability of ZooKeeper service. > > I could see one advantage of this approach is, you have a backup 'dataDir'. > > Administrator can use this if one is lost. > > > > > > -Rakesh > > -----Original Message----- > > From: Srinivasan Veerapandian > > [mailto:[email protected] > > ] > > Sent: 13 July 2015 15:01 > > To: [email protected] > > Subject: RE: ZooKeeper ensemble. Size and Impact ? > > > > Rakesh & Garry, > > > > > > > > Thanks for the information and details. From both of your responses > > I can see that, more failures will cause drop of quorum automatically. > > > > Is it so that only ensemble would be down but other functions would > > be up and running like data-sync ... ? Sorry If this is very basic question. > > > > > > > > I see a note below note, does this means we can form ensemble with > > leaderServes turned ON. > > > > Turning on leader selection is highly recommended when you have more > > than three ZooKeeper servers in an ensemble. > > http://zookeeper.apache.org/doc/r3.3.2/zookeeperAdmin.html > > > > My need to run only 2 ZKS as I'm ok with have +1 copy of the data. > > Is there a way to run a dummy ZKS in any of the instance ? > > > > > > > > Thanks, > > > > Srini > > > > -----Original Message----- > > From: Rakesh R [mailto:[email protected]] > > Sent: Monday, July 13, 2015 1:43 PM > > To: [email protected]; Srinivasan Veerapandian > > Subject: RE: ZooKeeper ensemble. Size and Impact ? > > > > > > > > Hi Srini, > > > > > > > > ZooKeeper service will be available if 'quorum' number of servers > > are running(simple majority voting factors). > > > > > > > > I could see, one of the reason to get a majority vote is to avoid > > "split-brain" problem. In a network failure we don't want the two > > parts of the system to continue as usual. We need only one part to > > continue and the other to understand that it is out of the cluster and keep > > quiet. > > > > > > > > The main reason for suggesting odd number is, with even there won't > > get much benefit to the tolerated failures in terms of majority. > > With 3 and 4 servers, we could see the majority is 2 and 3. But in > > both the cases, the tolerated number of failure is 1. > > > > > > > > Quorum = Leader + Followers, > > > > (2n+1) nodes can tolerate failure of 'n' nodes. > > > > > > > > For example, > > > > n=0, (2*0+1) -> 1 server = standalone. Here there is no quorum majority. > > > > -> 2 servers = majority is 2. So it needs min 2 servers > >to form quorum. Tolerated failure is 0, if >0 failure will drop > >quorum automatically. > > > > > > > > n=1, (2*1+1) -> 3 servers = majority is 2. So it needs min 2 servers > > to form quorum. Tolerated failure is 1, if >1 failures will drop > > quorum automatically. > > > > -> 4 servers = majority is 3. So it needs min 3 servers > >to form quorum. Tolerated failure is 1, if >1 failures will drop > >quorum automatically. > > > > > > > > n=2, (2*2+1) -> 5 servers = majority is 3. So it needs min 3 servers > > to form quorum. Tolerated failure is 2, if >2 failures will drop > > quorum automatically. > > > > -> 6 servers = majority is 4. So it needs min 4 servers > >to form quorum. Tolerated failure is 2, if >2 failures will drop > >quorum automatically. > > > > > > > > n=3, (2*3+1) -> 7 servers = majority is 4. So it needs min 4 servers > > to form quorum. Tolerated failure is 3, if >3 failures will drop > > quorum automatically. > > > > -> 8 servers = majority is 5. So it needs min 5 servers > >to form quorum. Tolerated failure is 3, if >3 failures will drop > >quorum automatically. > > > > > > > > > > > > -Rakesh > > > > > > > > -----Original Message----- > > > > From: Srinivasan Veerapandian > > [mailto:[email protected] > > ] > > > > Sent: 13 July 2015 11:48 > > > > To: [email protected]<mailto:[email protected]> > > > > Subject: ZooKeeper ensemble. Size and Impact ? > > > > > > > > Hi, > > > > > > > > We know ZK demands odd number of servers to provide reliability. > > > > My requirement on having zookeeper in my application is to "know the > > application status" from all the clients(Max 100). > > > > And today my application can support deployment 1+1(=2) to N+1(=100) > > Given this I would like to go with 2 ZK servers in two different > > instances because adding one more server for this purpose would be > > demand one more instance itself in my 1+1 deployment model. > > > > > > > > Questions: > > > > > > > > > > > > 1. What would happen to ensemble formed ? Would the service > > goes down automatically ? > > > > > > > > 2. What would be the impact if number ZK server instances are > > even (E.g. 2) > > > > > > > > How do I size a Zoo Keeper ensemble (cluster)? > > > > https://cwiki.apache.org/confluence/display/ZOOKEEPER/FAQ > > > > > > > > Designing a Zoo Keeper Deployment > > > > http://zookeeper.apache.org/doc/r3.1.2/zookeeperAdmin.html > > > > > > > > > > > > Thanks, > > > > Srini > > > > > >
