Improving System Availability through Failover

Failover: Failover is a backup operational mode used to enhance system stability and availability. When the primary component fails or is scheduled for downtime, the functions of system components (such as processors, servers, networks, or databases) are transferred to secondary system components.

Cold Backup: Cold backup refers to copying critical files to another location, using features or metrics/alerts to track failures. The system provides a new standby node in the event of a failure; however, cold backup is only suitable for stateless services. For backing up Oracle databases, cold backup is the fastest and safest method.

Hot Backup: This involves maintaining two active systems that share the same task roles, meaning the system operates normally while providing backup. The data between the two systems is nearly mirrored in real-time and contains the same information.

Warm Backup: This keeps two active systems, where the secondary system does not consume traffic unless a failure occurs.

Checkpoint (or similar to Redis snapshots): The system uses write-ahead logging (WAL) to record requests before processing tasks. The standby node recovers from the log during failover.

• Disadvantages
  • A large amount of log recovery can be time-consuming
  • Data loss since the last checkpoint
• User Cases: Storm, WhillWheel, Samza

Dual-host (or all-host) mode: This keeps two active systems behind a load balancer. The hosts operate in parallel, and data replication is bidirectional.