Failover | System Design

This video explains about failover and scenarios in which it can occur and how to avoid these situations.
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[amitkumar]

In system design, *failover* is a process that automatically transfers control from a failing component or system to a redundant or standby component. The goal of failover is to ensure continuity of service with minimal or no interruption in the event of hardware, software, or network failure.

# Key Aspects of Failover
1. Redundancy: Failover relies on having backup components that can take over in case the primary component fails. This can include backup servers, network paths, or storage systems.
2. Automatic Transition: The transition from the failed component to the backup component is typically automated, allowing the system to switch over quickly without requiring manual intervention.
3. Minimal Downtime: The design aims to reduce downtime to the lowest possible level, ideally making the failover process seamless to the end-users.
4. Health Monitoring: Systems that implement failover usually have monitoring tools to continuously check the health and status of components. When a failure is detected, the system triggers the failover process.

# Types of Failover
1. Active-Passive Failover: The primary component is active, while the backup component is passive and only becomes active when a failure is detected. This is common in database replication setups, where the primary database handles all requests and the secondary database is synchronized and ready to take over.
2. Active-Active Failover: Multiple components are active and share the load. If one fails, the others continue to operate and handle the increased load. This approach is common in load-balanced server clusters.
3. Manual Failover: Requires human intervention to switch to the backup system. This is less ideal for critical systems where immediate failover is required.
4. Geographical Failover: Involves switching to systems located in different geographic regions. This is useful for disaster recovery and to mitigate the risk of regional outages.

# Implementation Considerations
- Data Synchronization: Ensuring that the backup system has the most recent data and is in sync with the primary system to prevent data loss or inconsistency.
- Heartbeat Mechanism: A method of monitoring the status of the primary system by sending regular "heartbeat" signals. If these signals stop, it indicates a failure, triggering the failover.
- Testing and Validation: Regularly testing the failover process to ensure it works correctly and meets the required recovery time objectives (RTOs) and recovery point objectives (RPOs).
- Failback: The process of returning to the original component after a failover event has been resolved.

# Importance of Failover
Failover is crucial for maintaining high availability and reliability in systems, especially those that provide critical services, such as financial systems, healthcare applications, telecommunications, and cloud services. By ensuring that there is a backup in place, systems can minimize the impact of failures and continue to operate smoothly, maintaining user trust and service continuity.