Achieving High Availability - Fault Tolerance

There are several approaches to achieve HA. The most important of them is to make the system fault-tolerant.

What is fault tolerance?#

Fault tolerance is a system’s ability to stay up despite taking hits.

A fault-tolerant system is equipped to handle faults. Being fault-tolerant is an essential element in designing life-critical systems.

In a fault-tolerant system, out of several instances/nodes running a service, a few go offline and bounce back all the time. In case of these internal failures, the system can work at a reduced level without going down entirely.

An elementary example of a system like this is social networking platforms. In the case of backend node failures, a few services of the app, such as image upload, post likes, etc., may stop working. However, the application as a whole will still be up. This approach technically is also known as fail soft.

A highly available fault-tolerant service – Architecture#

A fault-tolerant system can be designed at the application and the deployment level. Since apps are typically deployed on the cloud in the modern web landscape, I discuss the deployment infrastructure in detail in my cloud computing course. It would be overkill to state everything in this one.

Also, this course, Web Application and Software Architecture 101, is part one of my Zero to Application Architect learning track, which enables you to be a pro at designing large-scale distributed services from knowing nothing. The Cloud computing 101 course follows this course in the learning track. Future courses will be released soon. I’ll talk more about this track at the end of this course, though.

So, to achieve high availability at the application level, the entire massive service is architecturally broken down into more granular loosely coupled services called microservices.

There are many upsides of splitting a big monolith into several microservices:

• Easy management and maintenance
• Ease of development
• Ease of adding new features to a service without affecting other services
• Scalability and high availability of the system

Every microservice takes the onus of running different features of an application such as photo upload, comment system, instant messaging, groups, marketplace, etc. In this case, even if a few services go down, the other services of the application are still up.