Spark has already over taken Hadoop (MapReduce) in general, because of benefits it provides in terms of faster execution in iterative processing algorithms.
A preview of our new research guide: The DZone Guide to the Java Ecosystem, from Ivar Grimstad about how to build microservices and use containers in Java.
There's more than one way to build microservices. Learn the Aggregator, Proxy, Chained, Branch, Shared Data, and Asynchronous Messaging Microservice Design Patterns
Different techniques can be used to handle multi-tenant data in Solr. This article discusses routing techniques you can use depending on the size and number of shards.