What are the principles of clustering: active-active and active-passive — what is the difference?

Active-active and active-passive are two main clustering principles for ensuring high availability and fault tolerance.

Active-active:

• All cluster nodes operate simultaneously and handle requests.
• Load is distributed among all active nodes.
• If one node fails, the others continue to operate without interruption.
• Requires data synchronization between nodes to avoid conflicts.

Active-passive:

• One node is active and handles requests, while others are in standby mode (reserve).
• If the active node fails, one of the passive nodes becomes active.
• Failover may take some time.
• Easier to implement as there is no simultaneous data access.

In the end, active-active provides higher performance and fault tolerance without downtime, but is more complex to implement. Active-passive is simpler but may have a small downtime during switch-over.