Understanding Active-Active Clustering: A Comprehensive Guide 101

While installing a server infrastructure, the common problem faced by administrators is to deploy a fault-tolerant and nonresistant design that has the potential to handle a single or multi-node failure. Most enterprises and companies require zero downtime for their customers to prevent node failure. This is where the concept of Active-Active Clustering comes into the picture. Active-Active Clustering architecture is a perfect approach to eliminate zero downtime. 

In this article, you will gain information about Active-Active Clustering. You will also gain a holistic understanding of the architecture of Active-Active Clustering, its advantages, and disadvantages, and comparison with Active-Passive Clustering.

What is Active-Active Clustering?

In Active-Active Clustering, a data adaptability architecture is deployed to distribute client tasks over two to three nodes in a cluster format to store data in a safe, protected, and accessible position. By keeping data in a cluster format, the workload of client data will remain protected from the possibility of an unplanned segment failure. The architecture of this clustering model is usually made up of more than two nodes that operate simultaneously to achieve redundancy and load balancing. 

With a load balancer, the workload is spread all over the nodes to avoid any idle node from being overloaded. The presence of more than two nodes will help improve the throughput and response times of service requests.

Some administrators are also called Active-Active clustering as dual-active clustering due to the availability of two nodes. All the idle or independent node points have their own replicated database server, and these nodes can access this copied database at any instance, resulting in high performance of applications running over the architecture.

Another benefit of using a replicated database is to experience the synchronization of data defined as continuous availability where a pair of companion nodes are present. If the primary node, for instance, fails to respond, then the secondary node comes into action and resumes the work of a primary node. Thus, the design will not suffer any node failure.

The job of a secondary node is to monitor all the traffic held by the primary node until it comes back from recovery mode and resumes its work. All the unissued transactions are kept and then resent to the presently operating node during the failover and failback process to prevent duplication and clean data thoroughly. 

Architecture of Active-Active Clustering

To understand the architecture of Active-Active Clustering, you can check the following infrastructure wherein the load balancer is connected to two HTTP nodes and multiple web clients. The purpose of a load balancer is to indirectly connect web clients to servers. The assignment of web clients to nodes in a cluster depends on the algorithm of a load balancer.

For example, if the load balancer is running a Round Robin algorithm, then the first client will go to the first node, the second client will go to the second node, the third client will be connected to a first node, and so on. For high availability and redundancy configuration during disaster recovery mode, all nodes must operate in a virtually identical manner. 

Advantages of Active-Active Clustering

The deployment of Active-Active clustering offers the following benefits:

• It provides high availability data architecture to annihilate a single point of failure, ensuring the full-time response of mission-critical applications, solutions, systems, and databases.
• It continuously maintains uptime longer than usual time.
• It enables the architecture to balance the load over a cluster of servers.
• It’s easy to increase the capacity of the methodology as traffic increases. Consequently, the network team can add additional nodes whenever it’s required. 
• As there’s no single point of failure in this system, the admin can experience high reliability and complete backup. 
• Provision of data monotony and resiliency as both failures and recovery become transparent across architecture and network.
• Presence of zero Recovery Point Object (RPO) and zero Recovery Time Objective (RTO) functionalities.

Active-Active vs Active-Passive Clustering

In Active-Active Clustering architecture, the units of a client are fastened to a load balancer to allocate workloads onto multiple active servers. Here, a user can access all the resources of computing servers during the regular function of architecture. 

In Active-Passive Clustering architecture, the systems of a client are joined to the main server instead of a load balancer to hold the full workload, while a backup server stays idle. It only gets activated in the event of an outage. Here, the backup server examines action during outage failure. 

Although the Active-Passive cluster also contains two nodes, it connects web clients directly to nodes, as shown in the following image. Unlike Active-Active clustering architecture, if the first node is active, the second node will remain in a standby position, and vice versa. Therefore, the second node or server takes full responsibility for the web clients when the primary server faces any failure or event outage. For this reason, the configuration setting of nodes or servers must be identical. 

Disadvantages of Active-active Clustering

The deployment of Active-Active clustering has the following limitations:

1) Requirement of Load Balancers

One of the most significant disadvantages suffered by administrators while deploying Active-Active clustering is that the load balancer bears all the workload of a web client. In the presence of a single load balancer, the network servers along with the user sessions would become slow or perform a limited operation during the failure of an independent load balancer. To avoid such a type of incident, it is recommended to embed more than one load balancer in the architecture of Active-Active clustering. 

2) Cost

The Active-Active clustering architecture approach is comparatively more expensive than the Active-Passive method due to the presence of additional load balancers. Moreover, the hardware and design of such type of infrastructure must be of premium quality to run all the operations smoothly. 

3) Maintenance

Active-Active clustering architecture requires 24/7 maintenance and monitoring of hardware, network nodes, and design to improve infrastructure reliability. 

Conclusion

Active-Active Clustering architecture is one of the most robust, trusted, reliable and upgradeable server setups currently in use. With this configuration, the admin team receives a complete view of the network status, infrastructure and load balancer output at all times. It also enables the team members to keep an eye on potential problems and unveil what solutions can be used to solve those issues. 

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