Re: 3 etcd nodes don't work well in single zone

Amit Kumar Gupta

Hi Tony,

All options are possible. You can run:

- one instance in a one-zone deployment
- one instance in one zone of a multi-zone deployment
- three instances in a one-zone deployment, will all three instances in the
same zone
- three instances in a multi-zone deployment, spreading out the instances
across zones
- three instances in a multi-zone deployment, where you still cram all
instances into one of the many zones

Running multiple instances improves availability in case one node dies, is
temporarily out of commission, being updated, etc. Multiple instances
incurs a performance cost though, since the data needs to be replicated
across nodes in the etcd cluster.

Running across multiple zones further improves availability and
fault-tolerance, since you're now resilient to even a whole zone (e.g.
hardware cluster) going down. This again incurs an additional performance
penalty, as network traffic between zones often suffers higher latency, as
well as a higher risk for network partitions.

I'm not sure where you found "Should be run as 1 node (but can NOT be run as
3 nodes) in environment with only one zone." I do not see it in the release
notes, but perhaps they were edited after you posted this question.

Amit, CF OSS Release Integration PM
Pivotal Software, Inc.

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