Basic Concepts

Scalability

Scalability describes the ability of a system to add or remove resources.

There are two types of scaling strategies:

1. Vertical Scaling
2. Horizontal Scaling

Availability

Availability is a measure of the time a system is operational and available to the users.

Availability	Downtime per year	Downtime per month	Downtime per week
90%	36.5 days	72 hours	16.8 hours
99%	3.65 days	7.2 hours	1.68 hours
99.9%	8.76 hours	43.2 minutes	10.1 minutes
99.99%	52.6 minutes	4.32 minutes	1.01 minutes
99.999%	5.26 minutes	25.9 seconds	6.05 seconds

Agility

Agility is the ability of a system to quickly adapt to changes.

Elasticity

Elasticity is the ability of a system to automatically and dynamically adjust resources based on the demand.

Fault Tolerance

Fault tolerance is the ability of a system to continue operating in the event of a failure.

Disaster Recovery

Disaster recovery is the ability of a system to recover from a catastrophic event.