Elastic Load Balancing & Auto Scaling Groups

Question 1

What is Scalability & High Availability ?

Answer 1

• Scalability means that an application / system 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
• Let’s deep dive into the distinction, using a call center as an example

Question 2

What is Vertical Scalability ?

Answer 2

• 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 a t2.large
• Vertical scalability is very common for non
  distributed systems, such as a database.
• There’s usually a limit to how much you can
  vertically scale (hardware limit)

Question 3

What is Horizontal Scalability ?

Answer 3

• 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 the cloud
  offerings such as Amazon EC2

Question 4

What is High Availability ?

Answer 4

• High Availability usually goes hand
  in hand with horizontal scaling
• High availability means running
  your application / system in at
  least 2 Availability Zones
• The goal of high availability is to
  survive a data center loss
  (disaster)

Question 5

Elaborate High Availability & Scalability For EC2 ?

Answer 5

• Vertical Scaling: Increase instance size (= scale up / down)
  
  • From: t2.nano - 0.5G of RAM, 1 vCPU
  • To: u-12tb1.metal – 12.3 TB of RAM, 448 vCPUs
• Horizontal Scaling: Increase number of instances (= 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

Question 6

Elaborate on Scalability vs Elasticity (vs Agility) ?

Answer 6

• Scalability: ability to accommodate a larger load by making the hardware
  stronger (scale up), or by adding nodes (scale out)
• Elasticity: once a system is scalable, elasticity means that there will be
  some “auto-scaling” so that the system can scale based on the load. This
  is “cloud-friendly”: pay-per-use, match demand, optimize costs
• Agility: (not related to scalability - distractor) new IT resources are only
  a click away, which means that you reduce the time to make those
  resources available to your developers from weeks to just minutes.

Question 7

Elaborate on Scalability vs Elasticity (vs Agility) ?

Answer 7

• Scalability: ability to accommodate a larger load by making the hardware
  stronger (scale up), or by adding nodes (scale out)
• Elasticity: once a system is scalable, elasticity means that there will be
  some “auto-scaling” so that the system can scale based on the load. This
  is “cloud-friendly”: pay-per-use, match demand, optimize costs
• Agility: (not related to scalability - distractor) new IT resources are only
  a click away, which means that you reduce the time to make those
  resources available to your developers from weeks to just minutes.

Question 8

What is load balancing?

Answer 8

• Load balancers are servers that forward internet traffic to multiple
  servers (EC2 Instances) downstream.

Question 9

Why use a load balancer?

Answer 9

• Spread load across multiple downstream instances
• Expose a single point of access (DNS) to your application
• Seamlessly handle failures of downstream instances * Do regular health checks to your instances
• Provide SSL termination (HTTPS) for your websites
• High availability across zones

Question 10

Why use an Elastic Load Balancer?

Answer 10

• An ELB (Elastic Load Balancer) is a managed load balancer
  
  • AWS guarantees that it will be working
  • AWS takes care of upgrades, maintenance, high availability
  • AWS provides only a few configuration knobs
• It costs less to setup your own load balancer but it will be a lot more
  effort on your end (maintenance, integrations)
• 4 kinds of load balancers offered by AWS:
  
  • Application Load Balancer (HTTP / HTTPS only) – Layer 7
  • Network Load Balancer (ultra-high performance, allows for TCP) – Layer 4
  • Gateway Load Balancer – Layer 3
  • Classic Load Balancer (retired in 2023) – Layer 4 & 7

Question 11

What’s an Auto Scaling Group?

Answer 11

• In real-life, the load on your websites and application can change
• In the cloud, you can create and get rid of servers very quickly
• The goal of an Auto Scaling Group (ASG) is to:
  
  • Scale out (add EC2 instances) to match an increased load
  • Scale in (remove EC2 instances) to match a decreased load
  • Ensure we have a minimum and a maximum number of machines running
  • Automatically register new instances to a load balancer
  • Replace unhealthy instances
• Cost Savings: only run at an optimal capacity (principle of the cloud)

Question 12

What are the Auto Scaling Groups – Scaling Strategies ?

Answer 12

• Manual Scaling: Update the size of an ASG manually
• Dynamic Scaling: Respond to changing demand
  • Simple / Step Scaling
    
    • When a CloudWatch alarm is triggered (example CPU > 70%), then add 2 units
    • When a CloudWatch alarm is triggered (example CPU < 30%), then remove 1
  • Target Tracking Scaling
    
    • Example: I want the average ASG CPU to stay at around 40%
  • Scheduled Scaling
    
    • Anticipate a scaling based on known usage patterns
    • Example: increase the min. capacity to 10 at 5 pm on Fridays

Question 13

Elaborate on Auto Scaling Groups
– Scaling Strategies ?

Answer 13

• Predictive Scaling
  
  • Uses Machine Learning
    to predict future traffic
    ahead of time
  • Automatically
    provisions the right
    number of EC2
    instances in advance
• Useful when your load
  has predictable time
• based patterns