Fault Tolerance At Scale

Fault tolerance is something that should be considered when developing anything, but it's particularly important when dealing with systems and applications that a business considers mission-critical. Without fault tolerance, a mission-critical system outage can have a cascading effect that wastes countless hours for employees and customers while developers work overtime to restore it.

Whether you're running in the cloud or locally, achieving fault tolerance at-scale is no easy feat. Let's walk through the methods and challenges you must address in order to get there.

What is Fault Tolerance?

The concept of fault tolerance is that a system, be it a computer, network, or cluster of clouds, should be able to operate uninterrupted, even if one or multiple components fail.

By creating a fault tolerant system, developers are able to prevent a single point of failure from disrupting service, which in turn improves availability and business continuity.

A fault tolerant system can operate uninterrupted, even when a component fails. Fault tolerance is something every developer strives for and it's becoming easier to achieve thanks to the increasing focus on loose coupling, containerization, and cloud development.

Fault tolerance plays a role in disaster recovery strategies, too, whether a company is trying to recover from a natural disaster (like one that took out power or hardware) or from any incident that destroys or compromises IT infrastructure.  

How Does Fault Tolerance Work?

Developers are able to create fault-tolerant systems by designing backup components that the system automatically switches to if the original, failed component is unavailable.

Examples include:

• Equivalent hardware running in parallel or mirroring the original hardware system so that it can take over in the event of a failure.
• Software instances that replicate another software instance so that operations can automatically redirect to the backup.
• Generators and other power sources that can turn on automatically in the event of a power failure.

By implementing redundancy, any component can be made fault tolerant.

Fault Tolerance vs. High Availability

Many organizations use fault tolerance and high availability interchangeably, but these are two different goals.

The definition of highly available is a service with minimal downtime. Meanwhile, a fault-tolerant system should never have any downtime.

Here's an analogy to make the difference clear: A car with a spare tire is highly available because the flat tire will require the car to pull over, but it minimizes downtime since the flat tire can be quickly installed.

Meanwhile, a self-sealing tire is an example of fault tolerance, because it allows you to keep driving even after a minor puncture, so you can head straight to the service station for a permanent fix.

If you can't decide when you should strive for high availability or fault tolerance, consider these two parameters:

• Downtime: Fault-tolerant systems are expected to work non-stop without any interruption. Highly available services allow a very small amount of service interruption. If you promise 99.999% availability, you promise to be down less than 5 minutes per year.
• Scope: Fault-tolerant systems require replicas, backups, and redundancy in the form of hardware, software, and power supplies. Highly available systems use a shared set of resources to help minimize downtime in the event of a failure.

Without a doubt, fault tolerance is more costly and more difficult to achieve, but it's necessary for mission-critical systems.

So, how do you achieve fault tolerance at scale?

Fault Tolerance at Scale

Before you seek to achieve fault tolerant design with any system, you need to weigh your tolerance for interruptions, the cost of interruptions, and the complexity of implementing fault tolerance.

When you decide that fault tolerance is valuable, the next step is implementing load balancing and failover solutions to help you achieve and maintain fault tolerance at scale.

Load balancing distributes an application across multiple nodes, making a single point of failure impossible.

Load balancers tend to optimize the workload, allowing you to improve performance and resiliency.

If a partial network failure occurs, load balancing will automatically shift the workload to the working server(s) so that your application can keep working without interruption.

Load balancing is ideal for smoothly handling spikes in activities and other variables that could slow down or interrupt a less fault tolerant system. Meanwhile, failover solutions help you stay alive even in an extreme situation, like the complete failure of your network.

A failover solution auto-activates a secondary platform to keep your application running. Meanwhile, your team will try to get the primary platform working again.

Achieving Fault Tolerance

Designing a fault tolerant system is no easy task, and it requires continuous maintenance, monitoring, and new implementations of backups to ensure that your system is truly fault tolerant, even as it scales.

Ultimately, the best team to design a fault tolerant solution is one that knows the intricacies of effectively planning and implementing fault tolerance.

Adservio is committed to building a resilient digital experience. If you need help achieving high availability or fault tolerance across your systems, our dedicated team of professionals can help.

Contact us today to discuss your needs and how we can apply our expertise to help you achieve your goals efficiently.