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From aaron morton <>
Subject Re: advice for EC2 deployment
Date Thu, 28 Apr 2011 10:11:23 GMT
If you are not going to be multi-region straight away, but wish to be in the near future I
would consider:

- 1 region
- 2 AZ's, with the same number of nodes
- Using the EC2Snitch as is, this will map to 1 cassandra DC and 2 cassandra Racks
- Using the NetworkTopology strategy 

For background see this excellent discussion from Peter and jump into NetworkTopologyStrategy.calculateNaturalEndpoints()
if you are so inclined.
In each DC the NTS will first spread the replicas across each rack (aws AZ). It then choses
replicas based on token order. 

I thinking you may be able to spread the replicas evenly across the racks (aws AZ), so that
a total failure of one AZ means the cassadra DC still has enough nodes in the other AZ to
continue working, this would mean a high RF in the DC (4 or 6 say). Not 100% sure, but I think
thats correct.

The reason for doing would be to make life easier in the future when you want to add another
DC. You would update the options for the NTS replication strategy and add the DC with the
correct RF, then run repair. 

Hope that helps. 

On 28 Apr 2011, at 01:38, William Oberman wrote:

> I think you're right about changing NetworkToplogyStrategy, but the timing isn't working
in my favor at this point.  I wonder how bad that will really be....
> On Wed, Apr 27, 2011 at 9:35 AM, Sasha Dolgy <> wrote:
> so can you not simply leverage a strategy that replicates data between
> "racks" and at some point in the future when you move to multi-dc
> upgrade the replication strategy to maintain the current replication
> and add in some replication between DC's ... ?
> i'll go re-read your posts to see if you've already tried this.  I
> vaguely remember Ellis saying it's not a good idea to switch
> NetworkTopologyStrategy ...
> On Wed, Apr 27, 2011 at 3:29 PM, William Oberman
> <> wrote:
> > Thanks Sasha.  Fortunately/unfortunately I did realize the default & current
> > behavior of the Ec2Snitch, but my application isn't multi-region capable
> > (yet), so I need to get intra-region redundancy.  And having a
> > SingleRegionEc2Snitch that did DC=ec2zone and RACK=??? would be much better
> > for me (for now).
> -- 
> Will Oberman
> Civic Science, Inc.
> 3030 Penn Avenue., First Floor
> Pittsburgh, PA 15201
> (M) 412-480-7835
> (E)

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