From what I understood, by reading the solrcloud examples is that you can declare a number of solr instances cores, for example 2, and than create on them a distributed index.
But what if by adding more items to the index, those 2 cores, servers are not big enough and I need to expand the index by adding another core? Would I need to stop all cores, delete the index and reindex everything, declaring this time that solrcloud may use 3 cores, servers? This would create downtime.
From what I’ve read sites like dailymotion use solr. How do they handle expanding on the index without downtime?
Under the assumption that expanding index means adding new shards, then the answer is that it is not possible to create new shards without a reindexing. This is because sharding is done using hashing and adding another bucket (shard) requires the hash function to be changed in order for new items into the shard.
As stated in http://wiki.apache.org/solr/SolrCloud#Re-sizing_a_Cluster it is a feature on the road map.