Aws Series High Availability and Scaling

Post Date : 2023-12-30T09:31:02+07:00

Modified Date : 2023-12-30T09:31:02+07:00

Category: systemdesign aws

Tags: aws

Vertical Scaling vs Horizontal Scaling

Vertical Scaling

Eg:

Increase your EC2 RAM
Increase your EC2 CPU
…

Horizontal Scaling

Eg:

Add new EC2
Add new EC2
…

But we dont’ only scale EC2, it should include other parts:

Database
VPC
AZ
…

The 3W’s of Scaling

What do we scale?

What sort of resource, we’re going to scale. How do we define template?

Where do we scale?

When applying the model, where does it go? Should we scale out database? Or Webservers?

When do we scale?

How do we know we need more? CloudWatch alarms can tell us it’s time to add more resources.

Launch Template

A launch template specifies the needed settings that go into building out an EC2 instance. It is a collection of settings you can configure so you dont’ have to walk through the EC2 wizard over and over.

It’s a heart of auto scaling feature.

Let’s compare Lauch Template with Configurations:

Launch Template

Capable of leveraging all EC2 auto scaling features.
Supports versioning
More granularity
AWS recommends this approach

Configuration

Only for certain EC2 auto scaling features
Immutable
Limited configuration options
Try not to use them

What can be included inside a Launch Template?

AMI
EC Instance Size
Security Groups
Potentially networking information( if you use autoscaling, this part should be set inside autoscaling group configuration)
Potentially UserData

Scaling EC2 Instances with Auto Scaling Groups

Creating a High Available application
Remember spread the resources out over multiple AZs and utilize load balancers

Auto Scaling Groups

Contain a collection of EC2 Instances that are treated as collective group for purposes of scaling and management.

Auto Scaling Steps

LifeCycle

Step Scaling

Simple Scaling

Relies on metrics for scaling needs

Example: Add 1 instances if CPU Utilization metric > 80%

Target Tracking

Uses a Scaling metric and value that ASG should maintain at all times

Eg: Maintain ASGAverageCPUUtilization = 50%

Instance Warm-up and CoolDown

Warm-Up: stops instances from being placed behind the load balancer, failing the health check, and being terminated prematurely

CoolDown: Pauses Auto Scaling for a set amount of time. Help you avoid runaway scaling events. -> prevent over doing auto scaling

Avoid Thrashing: You want to create instances quickly and spin them down slowly

Scaling Types

Reactive Scaling: Measure and determine if you need to create/remove resources
Schedule Scaling: Have a predictable workload, create a scaling event to get your resources ready to go before they’re actually needed -> shopping events(black Friday, Christmas, Hoildays)
Predictive Scaling: AWS uses it machine learning algorithms to determine when you’ll need to scale. They are reevaluated every 24 hours to create a forecast for the next 48 hours

Key Figures

Desired: initial value
Min: minimum value
Max: maximum value

Scaling Relational Databases

4 Types of Scaling

Vertical Scaling : resize
Scaling Storage: storage can be resized, but it’s only able to go up, not down
Read replicas: creating read-only copies of your data can help spread out the workload
Aurora serverless: We can offload autoscale to AWS. Excels with unpredictable workloads

Scaling Non-Relational Databases

DynamoDB

AWS does all the heavy lifting for you
Just 2 options: provisioned(predictable workload) and on-demand(sporadic workload)
You can switch between 2 options, but only twice per 24hours per table

Some figures

RCU(read capacity unit)

DynamoDB Unit of measurement for reads per second for an item up to 4KB in size.
One strongly consistent read per second
Two eventually consistent read per second

So how many RCUs for 1 strongly consistent read per second for object that are 7KB in size?

1 RCU = 4 KB/ 1 strongly consistent read Round up to the next nearest amount for the item size = 8KB/4KB = 2 RCU

WCU(write capacity unit)

DynanoDB Unit of measurement for writes per second for an item up to 1KB in size

So how many WCUs for 1 write per second for an object that is 3KB in size?

1 WCU = 1KB * 1 write per second
3KB * 1 WCU = 3 WCU