Migrating HDInsight HBase → Azure Cosmos DB (and/or Fabric Mirroring)

A field guide for migrating production HDInsight HBase clusters (HBase 2.x with Phoenix SQL, REST gateway, Thrift) to:

1. Azure Cosmos DB for NoSQL — primary target for new development; richest API, serverless option, Direct Lake-friendly via Fabric mirroring.
2. Azure Cosmos DB for Apache Cassandra — minimal-rewrite target when the existing data model is genuinely wide-column (CQL drop-in works for many HBase-via-Phoenix patterns).
3. Cosmos DB Mirroring in Microsoft Fabric — analytics overlay, not a write target. Mirrored Cosmos data appears as Delta in OneLake for Power BI / Spark / KQL.

Why this migration? HDInsight 4.0 has reached end-of-standard-support; HDInsight 5.x is the last classic generation, and HBase has no continuation in HDInsight on AKS. Microsoft's recommended landing zone for HDInsight HBase is Cosmos DB. For OLAP overlays previously served by Phoenix-on-HBase + HDI Spark, the recommended pattern is Cosmos DB (write) + Fabric Mirroring (read for analytics).