What is High Availability (HA)?

High Availability (HA) ensures your applications and systems remain operational with minimal downtime, even in case of failures.

Key points:

• Redundancy: Duplicate resources (servers, storage, networks) to handle failures.
• Failover: Automatic switching to backup resources if primary fails.
• Monitoring: Continuous health checks to detect failures.
• Recovery: Quick restoration of services to maintain uptime.

Example (kaptaindevops):

kaptaindevops runs a web app across multiple EC2 instances in different Availability Zones (AZs). If one AZ goes down, traffic automatically redirects to healthy instances, ensuring the app remains accessible.

What is Scalability?

Scalability is the ability of a system to handle growing or shrinking workloads efficiently.

Types of scalability:

1. Vertical Scaling (Scale-Up)
   • Increase resources of a single instance (CPU, RAM, storage)
   • Example: Upgrading t2.medium to t2.2xlarge
   • Easy but limited by instance type limits
2. Horizontal Scaling (Scale-Out)
   • Add more instances or servers to distribute load
   • Example: Adding more EC2 instances behind an Elastic Load Balancer (ELB)
   • Highly flexible, supports almost unlimited growth

Example (kaptaindevops):

During a product launch, kaptaindevops’s web traffic spikes. Horizontal scaling with Auto Scaling Groups (ASG) automatically launches new EC2 instances to handle the load, then scales down when traffic decreases.

High Availability vs Scalability