# Async Replication and Multi DC

**URL:** https://discuss.elastic.co/t/async-replication-and-multi-dc/22122
**Category:** Elasticsearch
**Created:** [February 12, 2015, 12:56am UTC](https://discuss.elastic.co/t/async-replication-and-multi-dc/22122 "2015-02-12T00:56:08Z")
**Posts on this page:** 1
**Showing post:** 2

<div class="post-metadata">

### Author: ![warkolm](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/warkolm/32/39224_2.png) [@warkolm](https://discuss.elastic.co/u/warkolm)
#### Post date: [February 12, 2015, 1:52am UTC](https://discuss.elastic.co/t/async-replication-and-multi-dc/22122/2 "2015-02-12T01:52:46Z")

</div>

Do not setup cross DC clusters, it's not recommended and ends up providing  
more headaches than it is worth.

You are better off replicating your data using either snapshot+restore or  
sending it to each individual cluster through your code.

On 12 February 2015 at 11:56, Parag Shah [parags@gmail.com](mailto:parags@gmail.com) wrote:

> Hi all,
> 
> ```
> I am trying to setup async replication with a multi-dc setup. Here is
> 
> ```
> 
> my scenario:
> 
> 1. I will have 3 nodes in each DC. For now, assume I have only 2 DCs.
> 2. I would like to use async replication, such that it writes  
> synchronously to the primary shard, but writes to only one node  
> asynchronously in the remote DC.
> 3. I would like to have 2 replicas. So, 3 copies in all.
> 
> I have looked at the cluster awareness settings here  
> [http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/modules-cluster.html](http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/modules-cluster.html).  
> However, I am not sure how it will work in practice, because if I simply  
> set "async" replication on each indexing request, it may choose to  
> replicate all 3 copies locally (including the primary) or even worse, 1  
> copy locally and 2 copies in the remote DC.
> 
> If I use the dc as the cluster awareness attribute, it will create only 1  
> copy in the local dc and another one in the remote DC. That won't satisfy  
> by 3 copies requirement.
> 
> If I create an additional attribute which is zone like this:
> 
> cluster.routing.allocation.awareness.attributes: dc, zone
> 
> and divide my DC into zone 1 (1 node?) and zone 2 (2 nodes?) and  
> vice-versa in the remote DC, I might be able to distribute the load  
> between zones in a DC and between DCs for the 3rd copy. However, there is  
> still the possibility that 2 of it's replica shards might be allocated in  
> the remote DC, which will prevent me from obtaining local (DC) quorums.
> 
> Can someone shed light on how shard allocation works when you have more  
> cluster allocation attributes than 1?
> 
> Also, if there is some known best practice for doing Async Replication  
> with MultiDC such that local quorums are always possible for reads/writes,  
> it will be greatly appreciated. In summary, I am looking for 3 copies  
> including primary. 2 in the local DC and 1 in the remote DC and want to  
> write synchronously only to the primary shard.
> 
> Thanks in advance,  
> Parag
> 
> --  
> You received this message because you are subscribed to the Google Groups  
> "elasticsearch" group.  
> To unsubscribe from this group and stop receiving emails from it, send an  
> email to [elasticsearch+unsubscribe@googlegroups.com](mailto:elasticsearch+unsubscribe@googlegroups.com).  
> To view this discussion on the web visit  
> [https://groups.google.com/d/msgid/elasticsearch/8f2a2c8c-4910-487c-9e5e-bfcfb96a235d%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/8f2a2c8c-4910-487c-9e5e-bfcfb96a235d%40googlegroups.com)  
> [https://groups.google.com/d/msgid/elasticsearch/8f2a2c8c-4910-487c-9e5e-bfcfb96a235d%40googlegroups.com?utm\_medium=email&utm\_source=footer](https://groups.google.com/d/msgid/elasticsearch/8f2a2c8c-4910-487c-9e5e-bfcfb96a235d%40googlegroups.com?utm_medium=email&utm_source=footer)  
> .  
> For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout).

--  
You received this message because you are subscribed to the Google Groups "elasticsearch" group.  
To unsubscribe from this group and stop receiving emails from it, send an email to [elasticsearch+unsubscribe@googlegroups.com](mailto:elasticsearch+unsubscribe@googlegroups.com).  
To view this discussion on the web visit [https://groups.google.com/d/msgid/elasticsearch/CAEYi1X9fun9091RLeXZci29dHFHwXs-L8X%3DzEsZ%2BxOerhg9%3DCA%40mail.gmail.com](https://groups.google.com/d/msgid/elasticsearch/CAEYi1X9fun9091RLeXZci29dHFHwXs-L8X%3DzEsZ%2BxOerhg9%3DCA%40mail.gmail.com).  
For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout).

---

_[View the full topic](https://discuss.elastic.co/t/async-replication-and-multi-dc/22122)._