Network resilience is crucial for maintaining continuous business operations. Failover mechanisms play a vital role in ensuring high availability and reliability of network services. Two primary failover strategies—Active-Active and Active-Standby—are commonly employed to achieve these goals.

Failover Fundamentals #

Failover mechanisms are designed to automatically switch to a standby system or component when the primary one fails, ensuring minimal downtime and uninterrupted service. The choice between Active-Active and Active-Standby configurations depends on the specific needs and architecture of an organization’s network.

Active-Active Failover #

In an Active-Active failover setup, multiple systems or components run concurrently, sharing the load and providing redundancy. Both (or all) systems are fully operational, and traffic is distributed among them. If one system fails, its load is seamlessly taken over by the remaining active systems, ensuring continuous availability.

Benefits:

• High Availability: With multiple active systems, the network remains available even if one system fails.
• Load Balancing: Traffic is evenly distributed across all active systems, optimizing resource utilization and performance.
• Scalability: Additional systems can be easily added to handle increased traffic and workload.

Implementation Considerations:

• Complexity: Active-Active configurations require sophisticated load balancing mechanisms to distribute traffic effectively.
• Cost: The need for multiple active systems and redundancy can be expensive in terms of hardware and maintenance.
• Synchronization: Ensuring data consistency and synchronization across all active systems is critical to prevent data loss or corruption.

Use Cases:

• Web Hosting: High-traffic websites use Active-Active configurations to distribute traffic across multiple servers, ensuring fast response times and high availability.
• Cloud Services: Cloud providers deploy Active-Active failover to offer seamless and uninterrupted services to their users.

Active-Standby Failover #

In an Active-Standby failover setup, one system (the active) handles all the traffic while the other (the standby) remains idle, ready to take over in case the active system fails. The standby system becomes active only during a failure event.

Benefits:

• Simplicity: Easier to implement and manage compared to Active-Active configurations.
• Cost-Effective: Requires fewer resources since the standby system is not actively handling traffic.
• Predictable Failover: The failover process is straightforward, with a clear primary and backup system.

Implementation Considerations:

• Failover Time: There might be a brief interruption as the standby system takes over the active role.
• Underutilization: The standby system remains idle during normal operations, leading to potential underutilization of resources.
• Maintenance: Regular testing and maintenance of the standby system are essential to ensure it functions correctly during a failover.

Use Cases:

• Databases: Critical databases often use Active-Standby configurations to ensure data integrity and availability during failover.
• Enterprise Applications: Business-critical applications that require predictable and straightforward failover mechanisms.

Choosing the Right Failover Strategy #

Selecting between Active-Active and Active-Standby failover strategies depends on several factors, including:
Availability Requirements: For environments requiring high availability and minimal downtime, Active-Active configurations are preferred.
Budget Constraints: Active-Standby setups are more cost-effective and may be suitable for smaller organizations with limited budgets.
Traffic Load: High-traffic environments benefit from the load balancing capabilities of Active-Active configurations.
Complexity and Management: Active-Standby setups are simpler to manage, making them suitable for organizations with limited IT resources.

How to implement failover with RELIANOID #

Implementing active-active and active-passive failover with RELIANOID involves using load balancing methods like Global Server Load Balancing (GSLB) for active-active configurations and stateful clustering for active-passive configurations. Here’s a detailed guide on how to achieve both setups:

Active-Active Failover with GSLB #

Overview: Active-active failover ensures that all servers are actively handling traffic, distributing the load among multiple servers, thus providing high availability and load balancing.

Prerequisites:

• RELIANOID installed on multiple servers.
• Public IP addresses for each server.
• DNS control to manage GSLB records.

Steps:

1. Set Up GSLB:

• Log in to the RELIANOID web interface.
• Navigate to GSLB > Farms and create a new farm.

2. Configure GSLB:

• Add DNS zones and backends (RELIANOID load balancers in this case) to the GSLB farm, specifying the IP addresses of the servers that will be part of the active-active setup.
• Configure the health checks to ensure each server is operational. These health checks will periodically check the health of each backend server.

3. DNS Configuration:
Configure your DNS provider to use the GSLB farm IP address. This ensures that DNS requests are routed through the GSLB, which in turn distributes traffic to the available servers.

4. Monitor and Adjust:

• Regularly monitor the performance and health of your GSLB setup through the RELIANOID interface.
• Adjust the load balancing algorithm if necessary (e.g., Round Robin, Least Connections) to optimize performance.

Active-Passive Failover with Stateful Clustering #

Overview: Active-passive failover involves one server actively handling traffic while the other server(s) remain in standby mode. If the active server fails, a passive server takes over.

Prerequisites:

• RELIANOID installed on at least two servers.
• Network configuration to allow communication between the servers.
• Carp and gratuitous ARP traffic allowed.

Steps:

1. Cluster Configuration:

• Log in to the RELIANOID web interface on both servers.
• Navigate to System > Cluster on each server.
• Configure one server as the Master and the other as the Slave.

2. Sync Configuration:

• Ensure that configuration files and state information are synchronized between the master and slave servers.
• Use the built-in synchronization tools in RELIANOID to keep the configurations identical.

3. Failover Testing:

• Test the failover mechanism by simulating a failure on the master server.
• Verify that the slave server takes over and that session states are preserved.

4. Monitor and Maintain:

• Regularly monitor the cluster status through the RELIANOID interface.
• Ensure that synchronization remains active and that any configuration changes are propagated to both servers.

Example Configuration for Stateful Clustering (Active-Passive) #

Cluster Setup:

• On the master server: System > Cluster > Configure as Master.
• On the slave server: System > Cluster > Configure as Slave.

Synchronization:

• Ensure configuration and state synchronization are enabled.
• Regularly sync configurations manually if needed or use automatic synchronization features.

Enable Stateful Failover:

• Configure stateful failover settings to preserve session states.

Conclusion #

Both Active-Active and Active-Standby failover strategies play crucial roles in ensuring network resilience and high availability. Understanding their benefits, use cases, and implementation considerations helps organizations choose the right approach to meet their specific needs. Whether aiming for maximum availability with Active-Active configurations or seeking a cost-effective and straightforward solution with Active-Standby setups, implementing a robust failover mechanism is essential for maintaining uninterrupted network services and achieving business continuity.

By following these steps, you can set up both active-active and active-passive failover configurations in RELIANOID to ensure high availability and load balancing for your applications.