I have recently started running on EC2 and am seeing quite a few
ConnectionLoss exceptions.  Should I just catch these and retry?  Since I
assume that eventually, if the shit truly hits the fan, I will get a

On Mon, Jul 6, 2009 at 11:35 AM, Ted Dunning <ted.dunn...@gmail.com> wrote:

> We have used EC2 quite a bit for ZK.
> The basic lessons that I have learned include:
> a) EC2's biggest advantage after scaling and elasticity was conformity of
> configuration.  Since you are bringing machines up and down all the time,
> they begin to act more like programs and you wind up with boot scripts that
> give you a very predictable environment.  Nice.
> b) EC2 interconnect has a lot more going on than in a dedicated VLAN.  That
> can make the ZK servers appear a bit less connected.  You have to plan for
> ConnectionLoss events.
> c) for highest reliability, I switched to large instances.  On reflection,
> I
> think that was helpful, but less important than I thought at the time.
> d) increasing and decreasing cluster size is nearly painless and is easily
> scriptable.  To decrease, do a rolling update on the survivors to update
> their configuration.  Then take down the instance you want to lose.  To
> increase, do a rolling update starting with the new instances to update the
> configuration to include all of the machines.  The rolling update should
> bounce each ZK with several seconds between each bounce.  Rescaling the
> cluster takes less than a minute which makes it comparable to EC2 instance
> boot time (about 30 seconds for the Alestic ubuntu instance that we used
> plus about 20 seconds for additional configuration).
> On Mon, Jul 6, 2009 at 4:45 AM, David Graf <david.g...@28msec.com> wrote:
> > Hello
> >
> > I wanna set up a zookeeper ensemble on amazon's ec2 service. In my
> system,
> > zookeeper is used to run a locking service and to generate unique id's.
> > Currently, for testing purposes, I am only running one instance. Now, I
> need
> > to set up an ensemble to protect my system against crashes.
> > The ec2 services has some differences to a normal server farm. E.g. the
> > data saved on the file system of an ec2 instance is lost if the instance
> > crashes. In the documentation of zookeeper, I have read that zookeeper
> saves
> > snapshots of the in-memory data in the file system. Is that needed for
> > recovery? Logically, it would be much easier for me if this is not the
> case.
> > Additionally, ec2 brings the advantage that serves can be switch on and
> off
> > dynamically dependent on the load, traffic, etc. Can this advantage be
> > utilized for a zookeeper ensemble? Is it possible to add a zookeeper
> server
> > dynamically to an ensemble? E.g. dependent on the in-memory load?
> >
> > David
> >

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