134 lines
7.5 KiB
Markdown
134 lines
7.5 KiB
Markdown
# Elastic Load Balancing & Auto Scaling Groups
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- [Elastic Load Balancing & Auto Scaling Groups](#elastic-load-balancing--auto-scaling-groups)
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- [Scalability & High Availability](#scalability--high-availability)
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- [Vertical Scalability](#vertical-scalability)
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- [Horizontal Scalability](#horizontal-scalability)
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- [High Availability](#high-availability)
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- [High Availability & Scalability For EC2](#high-availability--scalability-for-ec2)
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- [Scalability vs Elasticity (vs Agility)](#scalability-vs-elasticity-vs-agility)
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- [What is load balancing?](#what-is-load-balancing)
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- [Why use a load balancer?](#why-use-a-load-balancer)
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- [Why use an Elastic Load Balancer?](#why-use-an-elastic-load-balancer)
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- [What’s an Auto Scaling Group?](#whats-an-auto-scaling-group)
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- [Auto Scaling Groups Scaling Strategies](#auto-scaling-groups-scaling-strategies)
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- [ELB & ASG Summary](#elb--asg-summary)
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## Scalability & High Availability
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- Scalability means that an application / system can handle greater loads by adapting.
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- There are two kinds of scalability:
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- Vertical Scalability
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- Horizontal Scalability (= elasticity)
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- Scalability is linked but different to High Availability
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- Let’s deep dive into the distinction, using a call center as an example
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## Vertical Scalability
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- Vertical Scalability means increasing the size of the instance
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- For example, your application runs on a t2.micro
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- Scaling that application vertically means running it on a t2.large
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- Vertical scalability is very common for non distributed systems, such as a database.
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- There’s usually a limit to how much you can vertically scale (hardware limit)
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## Horizontal Scalability
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- Horizontal Scalability means increasing the number of instances / systems for your application
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- Horizontal scaling implies distributed systems.
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- This is very common for web applications / modern applications
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- It’s easy to horizontally scale thanks the cloud offerings such as Amazon EC2
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## High Availability
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- High Availability usually goes hand in hand with horizontal scaling
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- High availability means running your application / system in at least 2 Availability Zones
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- The goal of high availability is to survive a data center loss (disaster)
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## High Availability & Scalability For EC2
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- Vertical Scaling: Increase instance size (= scale up / down)
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- From: t2.nano - 0.5G of RAM, 1 vCPU
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- To: u-12tb1.metal – 12.3 TB of RAM, 448 vCPUs
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- Horizontal Scaling: Increase number of instances (= scale out / in)
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- Auto Scaling Group
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- Load Balancer
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- High Availability: Run instances for the same application across multi AZ
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- Auto Scaling Group multi AZ
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- Load Balancer multi AZ
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## Scalability vs Elasticity (vs Agility)
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| Scalability | Elasticity | Agility |
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| --------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
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| ability to accommodate a larger load by making the hardware stronger (scale up), or by adding nodes (scale out) | 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 | (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. |
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## What is load balancing?
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- Load balancers are servers that forward internet traffic to multiple servers (EC2 Instances) downstream.
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### Why use a load balancer?
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- Spread load across multiple downstream instances
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- Expose a single point of access (DNS) to your application
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- Seamlessly handle failures of downstream instances
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- Do regular health checks to your instances
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- Provide SSL termination (HTTPS) for your websites
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- High availability across zones
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### Why use an Elastic Load Balancer?
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- An ELB (Elastic Load Balancer) is a managed load balancer
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- AWS guarantees that it will be working
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- AWS takes care of upgrades, maintenance, high availability
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- AWS provides only a few configuration knobs
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- It costs less to setup your own load balancer but it will be a lot more effort on your end (maintenance, integrations)
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- 3 kinds of load balancers offered by AWS:
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- Application Load Balancer (HTTP / HTTPS only) – Layer 7
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- Network Load Balancer (ultra-high performance, allows for TCP) – Layer 4
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- Classic Load Balancer (slowly retiring) – Layer 4 & 7
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## What’s an Auto Scaling Group?
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- In real-life, the load on your websites and application can change
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- In the cloud, you can create and get rid of servers very quickly
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- The goal of an Auto Scaling Group (ASG) is to:
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- Scale out (add EC2 instances) to match an increased load
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- Scale in (remove EC2 instances) to match a decreased load
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- Ensure we have a minimum and a maximum number of machines running
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- Automatically register new instances to a load balancer
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- Replace unhealthy instances
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- Cost Savings: only run at an optimal capacity (principle of the cloud)
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### Auto Scaling Groups Scaling Strategies
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- Manual Scaling: Update the size of an ASG manually
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- Dynamic Scaling: Respond to changing demand
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- Simple / Step Scaling
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- When a CloudWatch alarm is triggered (example CPU > 70%), then add 2 units
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- When a CloudWatch alarm is triggered (example CPU < 30%), then remove 1
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- Target Tracking Scaling
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- Example: I want the average ASG CPU to stay at around 40%
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- Scheduled Scaling
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- Anticipate a scaling based on known usage patterns
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- Example: increase the min. capacity to 10 at 5 pm on Fridays
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- Predictive Scaling
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- Uses Machine Learning to predict future traffic ahead of time
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- Automatically provisions the right number of EC2 instances in advance
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- Useful when your load has predictable time - based patterns
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## ELB & ASG Summary
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- High Availability vs Scalability (vertical and horizontal) vs Elasticity vs Agility in the Cloud
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- Elastic Load Balancers (ELB)
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- Distribute traffic across backend EC2 instances, can be Multi-AZ
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- Supports health checks
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- 3 types: Application LB (HTTP – L7), Network LB (TCP – L4), Classic LB (old)
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- Auto Scaling Groups (ASG)
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- Implement Elasticity for your application, across multiple AZ
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- Scale EC2 instances based on the demand on your system, replace unhealthy
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- Integrated with the ELB
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* * *
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[<img align="center" src="../images/back-arrow.png" height="20" width="20"/> EC2 Instance Storage](./ec2_storage.md) [<img align="center" src="../images/list.png" height="30" width="30"/> List](../README.md) [Amazon S3 <img align="center" src="../images/forward-arrow.png" height="20" width="20"/>](./s3.md)
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