Active-Passive failover is a high availability (HA) configuration designed to ensure system uptime and minimize data loss in the event of a failure. Here’s a detailed explanation of how it works:
Overview
In an Active-Passive failover setup, there are at least two nodes: one active node and one passive node. The active node handles all the traffic and processes all requests, while the passive node remains on standby, ready to take over if the active node fails.
Mechanism
Primary and Standby Nodes:
Active Node: This is the primary node that handles all the incoming traffic and processes all requests.
Passive Node: This is the standby node that remains idle but is configured identically to the active node. It does not handle any traffic or requests unless the active node fails.
Heartbeat Monitoring:
The active and passive nodes are connected via heartbeat cables or software mechanisms that continuously monitor the health of the active node. This is often referred to as a "heartbeat" or "pulse" signal.
As long as the passive node detects the heartbeat from the active node, it remains idle.
Failover Process:
Detection: If the passive node detects a failure in the active node (e.g., the heartbeat signal stops), it initiates the failover process.
Switching: The passive node takes over the role of the active node. This involves mounting shared disks, starting necessary services, and taking over the IP address of the active node to ensure seamless transition.
Notification: The system may also send alerts to administrators or technicians to inform them of the failover event and the need to bring the original active node back online.
Manual vs. Automated Failover:
Automated Failover: The failover process is fully automated, with the passive node taking over immediately upon detecting a failure.
Manual Failover: The system alerts administrators, who then manually initiate the failover process. This can result in longer downtime compared to automated failover.
Advantages
Increased Availability: The passive node is always ready to take over, ensuring minimal downtime.
Cost-Effective: Only one node is actively handling traffic, which can reduce operational costs compared to active-active configurations.
Simpler Implementation: Active-passive setups are generally easier to implement and manage compared to active-active configurations, which require load balancing and more complex synchronization.
Disadvantages
Potential Downtime: There is a brief period of downtime during the switch from the active to the passive node.
Underutilization: The passive node remains idle most of the time, leading to underutilization of resources.
