Understanding Active-Passive, Active/Active load balancing

active/active and active/passive pair

As businesses today, thanks to the extended use of the internet run a 24/7 operation, needs networks to be designed to assure high availability (H/A). The two most popular methods adopted by network managers today to achieve this are to use clustering to deal with failover (Active/Passive Mode) and load balancing. Active/Active mode is employed to provide for database or session replication and to support redundancy. Load balancers can be placed in the network to direct server requests according to server performance and the method of traffic distribution chosen for example round robin.  In certain cases network managers prefer to place the network load balancers outside the cluster to provide for increased horizontal scalability.

As the amount of commerce businesses do over the internet increases it becomes even more important to cluster servers and at the same time to deploy load balancers to take advantage of the inherent fault tolerance that they offer. First of all its good practice to analyze the critical services that you have in your network. These can include your database servers, e commerce services and mail system, for example Microsoft Exchange, set yourself to the task to cluster these to take advantage of the high availability this will offer.

Active passive configuration and advantages

Next you should turn your attention to your load balancers, an Active/Passive configuration will offer you many advantages so you should consider buying a pair of load balancers and configure them in H/A mode. This done the primary load balancer distributes the network traffic to the most suitable server while the second load balancer operates in listening mode to constantly monitor the performance of the primary load balancer, ready at any time to step in and take over the load balancing duties should the primary load balancer be in difficulty and failing.

By operating load balancers in Active/Passive mode the ability to maintain uninterrupted service for your customers is achievable. Another advantage that this configuration presents is the ability to deal with either planned or unplanned service outages. As business today requires 24/7 internet service for customers or staff to suffer any outage at all is costly for the business in terms of trade lost as well as damage to the businesses image.

Active/ Active configuration and advantages

In Active/Active mode two or more servers aggregate the network traffic load and working as a team distributes it to the network servers. The load balancers can also remember information requests from users and keep this information in cache. Should the user return looking for the same information the user will be locked onto the load balancer that previously served them and the information provided again from the cache without the network server having to respond therefore reducing network traffic load.

The one potential disadvantage of setting up your load balancers in Active/Active mode is that you run them near full capacity. What this would mean is that unless you have a spare load balancer to commission and make operational in the network in the event of a load balancer failure your network servers would appear to run slows of user sessions would time out.

Have you now done everything? No

In the same way as an aircraft can be switched to autopilot when cruising, your network with its server clusters and network load balancers is “fit for flight”. However as you would hardly consider being a passenger in an aircraft with no crew, the role of the network administrator is vital too. Your network administrator needs to have complete view of network status, application performance and load balancer throughput at all times. Leading load balancers like KEMP Technologies Load Masters provide advanced statistics conveniently displayed on an easy to understand dashboard. The network administrator can drill down to look at a potential or actual problem in great detail and decide what remedial tactics to employ. Another vital feature found in the Load Masters when configured in H/A active passive mode is the ability to use stateful failover to ensure minimum service disruption.

The way this works is that the passive load balancer is constantly monitoring the user sessions as well as the performance of the active device. Should the primary device fail the passive back up load balancer kicks in, takes the sessions from the active load balancer and seamlessly continues to serve the users. While expensive load balancers such as F5 and Radware provide this support it is not often found in the more economic load balancers. Fortunately for its users KEMP Technologies Load Masters offer this feature across both the virtual as well as physical load balancers.