FAILOVER OF APPLICATION SERVICES

The disclosure is directed to a failover mechanism for failing over an application service, e.g., a messaging service, from servers in a first region to servers in a second region. Data is stored as shards in which each shard contains data associated with a subset of the users. Data access requests are served by a primary region of the shard. A global shard manager manages failing over the application service from a current primary region to a secondary region of the shard. A leader service in the application service replicates data associated with the application service from the primary to the secondary region, and ensures that the state of various other services of the application service in the secondary region is consistent. The leader service confirms that there is no replication lag between the primary and secondary regions and fails over the application service to the secondary region.