Understand terms such as High Availability, Scalability, Elasticity, Agility, Fault Tolerance, and Disaster Recovery

High Availability (HA)

High availability refers to systems that are durable and likely to operate continuously without failure for a long time. The term implies that parts of a system have been fully tested and, in many cases, that there are accommodations for failure in the form of redundant components.

A highly available application absorbs fluctuations in availability, load, and temporary failures in the dependent services and hardware. The application continues to operate at an acceptable user and systemic response level, as defined by business requirements or application service-level agreements (SLAs).

Scalability 

Scalability is an attribute that describes the ability of a process, network, software or organization to grow and manage increased demand. A system, business or software that is described as scalable has an advantage because it is more adaptable to the changing needs or demands of its users or clients.


Scalability is often a sign of stability and competitiveness, as it means the network, system, software or organization is ready to handle the influx of demand, increased productivity, trends, changing needs and even presence or introduction of new competitors.

Elasticity

Elastic computing is a concept in cloud computing in which computing resources can be scaled up and down easily by the cloud service provider. Elastic computing is the ability of a cloud service provider to provision flexible computing power when and wherever required. The elasticity of these resources can be in terms of processing power, storage, bandwidth, etc.

Agility

Fault Tolerance (FT)

A Fault Tolerant system is extremely similar to HA, but goes one step further by guaranteeing zero downtime. HA still comes with a small portion of downtime, hence the ideal of a perfect HA strategy reaching “five nines” rather than 100% uptime. The time it takes for the intermediary layer, like the load balancer or hypervisor, to detect a problem and restart the VM can add up to minutes or even hours over the course of yearly runtime.

Disaster Recovery (DR)

DR goes beyond FT or HA and consists of a complete plan to recover critical business systems and normal operations in the event of a catastrophic disaster like a major weather event (hurricane, flood, tornado, etc), a cyberattack, or any other cause of significant downtime. HA is often a major component of DR, which can also consist of an entirely separate physical infrastructure site with a 1:1 replacement for every critical infrastructure component, or at least as many as required to restore the most essential business functions.