Solr search and index rate optimization

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i wanted to ask that i need to index after evey 15 min with hard commit
(real time records) and currently have 5 zookeeper instances and 2 solr
instances in one machine serving 200 users with 32GB RAM. whereas i wanted
to serve more than 10,000 users so what should be my machine specs and what
should be my architecture for this much serve rate along with index rate.
my index size is 30GB increases gradually. Thankyou in advance and i am
newbee hoping to get response