Implementing Decentralized Per-Partition Automatic Failover in Azure Cosmos DB

Josh Rowe; Mikael Horal; Hari Sudan Sundar; Muthukumaran Arumugam; Burak Kose; Sravani Mitra Palivela; Geni Marsh; Varun Jain; Abhishek Kumar; Dhaval Patel

arXiv · 2505.14900

Implementing Decentralized Per-Partition Automatic Failover in Azure Cosmos DB

Josh Rowe·Mikael Horal·Hari Sudan Sundar·Muthukumaran Arumugam·Burak Kose·Sravani Mitra Palivela·Geni Marsh·Varun Jain·Abhishek Kumar·Dhaval Patel

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Abstract

Azure Cosmos DB is a cloud-native distributed database, operating at a massive scale, powering Microsoft Cloud. Think 10s of millions of database partitions (replica-sets), 100+ PBs of data under management, 20M+ vCores. Failovers are an integral part of distributed databases to provide data availability during outages (partial or full regional outages). While failovers within a replica-set within a single region are well understood and commonly exercised, geo failovers in databases across regions are not as common and usually left as a disaster recovery scenario. An upcoming release of Azure Cosmos DB introduces a fine grained (partition-level) automatic failover solution for geo failovers that minimizes the Recovery Time Objective (RTO) and honors customer-chosen consistency level and Recovery Point Objective (RPO) at any scale. This is achieved thanks to a decentralized architecture which offers seamless horizontal scaling to allow us to handle outages ranging from node-level faults to full-scale regional outages. Our solution is designed to handle a broad spectrum of hardware and software faults, including node failures, crashes, power events and most network partitions, that span beyond the scope of a single fault domain or an availability zone.

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BibTeX RIS

Josh Rowe, Mikael Horal, Hari Sudan Sundar, Muthukumaran Arumugam, Burak Kose, Sravani Mitra Palivela, Geni Marsh, Varun Jain, Abhishek Kumar, Dhaval Patel. 2025-05-20. Implementing Decentralized Per-Partition Automatic Failover in Azure Cosmos DB. https://arxiv.org/abs/2505.14900

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