Skip to content

High Availability and Scalability

  • Scalability means that an application / systen can handle greater loads by adapting.

  • There are two kinds of scalability:

    • Vertical scalability
    • Horizontal scalability (= elasticity)

  • Scalability is linked but different to High Availability

Vertican Scalability

  • Vertical scalability means increasing the size of the instance
  • For example, your application runs on a t2.micro
  • Scaling that application vertically means running it on t2.large
  • Vertical scalability is very common for non distributed systems, such as a database.
  • RDS, ElastiCache are services that can scale vertically.
  • There's usually a limit to how much you can vertically scale (hardware limit)

Horizontal Scalability

  • Horizontal Scalability means increasing the number of instances / systems for your application
  • Horizontal scaling implies distributed systems This is very common for web applications / modern applications
  • It's easy to horizontally scale thanks to the cloud offerings such as Amazon EC2

High Availability

  • High availability usually goes hand in hand with horizontal scalin
  • High availability means running your application /system in at least 2 data centers (AZs)
  • The goal of high availability is to survive a data center loss
  • The high availability can be passive (for RDS Multi AZ for example)
  • The high availability can be active (for horizontal scaling)

High Availability & Scalability for EC2

  • Vertical Scaling: Increase instance size (= scale up/down)
    • From: t2.nano - 0.5G of ram, 1 vCPU
    • To: u-12tb1.metal - 12.3TB of ram, 448 vCPUs
  • Horizontal scaling: increase number of isntances (= scale out/in)
    • Auto Scaling Group
    • Load Balancer
  • High Availability: Run instances for the same application across multi AZ
    • Auto Scaling Group multi AZ
    • Load Balancer multi AZ