Can we have cassandra only nodes and solr enabled

I just started with solr and would like your suggestion in below scenario. We have 2 data centers with 3 nodes in each data center(both in different aws regions for location advantage). We have a requirement for which they asked me if we can have 2 solr nodes in each data center. so it will be 2 solr nodes and 1 cassandra only node in each data center. I want to understand if its fine to have this kind of setup and I am little confused whether solr nodes will have data on it along with the indexes? does all 6 nodes share data and 4 solr nodes will have indexes on it along with data? Kindly provide some information on this. Thanks.

Short answer is no, this will not work. If you turn on DSE Search on one node in a DC you need to turn it on for all the nodes in the DC.

But why??

DSE Search builds lucene indexes on the data that is stored local to a node. Say you have a 3 node DC with RF1 (the node only has 1/3rd of the data) and you only turn on search on one of the nodes. 1/3 of your search queries will fail.

So I should just turn search on everywhere?

If you have a relatively small workloads with loose SLA's (both c* and search) and/or if you are over provisioned, you may be fine turning on Search on your main Cassandra nodes. However, in many cases with heavy c* workloads and tight SLA's, Search queries will negatively affect cassandra performance (because they are contending against the same hardware).

I need search nodes in both Physical DC's

If you want search enabled only in two out of your three nodes in a physical DC, the only way to do this is to actually split up your physical DC into two logical DC's. In your case you would have:

US - Cassandra

US - Search

Singapore - Cassandra

Singapore - Search

This gives you geographic locality for your search and c* queries and also provides workload isolation between your c* and search workloads since they contend against different OS Subsystems.