Well, replicas _can_ cross data centers, there's nothing explicitly preventing it. But the network latency will cause "interesting" problems, not to mention ZooKeeper Quorum sensing being challenging. But your description is accurate, there's no such thing as a "read only replica" in SolrCloud.
That said, if you're just looking at doing the same thing you're doing pre Solr 4.0, then you can just go ahead and set it up like your older version; replication still works just like it did before, and it's not going away. In fact, it's used in SolrCloud to handle replica syncing under certain circumstances. SolrCloud is an alternate model that overcomes some of the pain points of managing (particularly sharded) installations that have things like NRT requirements etc. But there's nothing in Solr 4.x that _requires_ that you operate in "cloud mode", you can use master/slave just like 3.x for instance if it suits your problem better. Best, Erick On Sat, Sep 27, 2014 at 7:42 PM, Sandeep Tikoo <sti...@digitalriver.com> wrote: > Hi- > > I have been reading up on SolrCloud and it seems that it is not possible > to have a cross-datacenter read-only slave anymore but wanted to ask here > to be sure. > We currently have a pre Solr 4.0 installation with the master instance in > our US mid-west datacenter. The datacenter in Europe has read-replicas > which pull data using solr.ReplicationHandler. We wanted to upgrade to > SolrCloud. As far as I have been able to figure out, with SolrCloud you > cannot have a read-only replica anymore. A replica has to be able to become > a leader and writes against all replicas for a shard have to succeed. > Because of the a strong consistency model across replicas, it seems that > replicas cannot be across datacenters anymore. > > So my question is, how can we have a read-ony replica in a remote > datacenter in Solr 4.0+ similar to pre Solr 4.0? Is it not possible anymore > without doing it all yourself? > > cheers, > Tikoo > >
