Elastic Load Balancer & Auto scaling groups
Lets learn about ELB and ASG
Difference between Scalability, High Availability, Elasticity and Agility.
Scalability :
An app / system can handle greater loads by adapting. There is 2 types of scalability :
Horizontal Scalability -> Increasing your number of resources (nodes, instances) - (Scale out/in) - aka elasticity. => Very common for web applications and modern applications
Vertical Scalability -> Making your current resources better (increasing the size) - Upgrading ( scale up / down) e.g. going from t2.micro to t2.large => Very common for non distributed systems such as database and the it has the (hardware limit)
Elasticity :
This means that the system will have auto-scaling So it will scale up when the demand is high and scale down when the demand is low, This is extremely cost-efficient and useful for on-demand or pay-per-use things as it can save a lot of money and you don't have to keep "guessing capacity"
Agility :
Means that you can do things very quickly because you can get/delete IT resources in a matter of seconds And is not related to scalability - Distractor
High Availability :
Running your application or system across multiple Availability Zones ( in a minimum of Availability Zones).
Elastic Load Balancer
Basically, the load balancer will distribute the traffic across multiple targets/servers and it can across multiple Availability Zones.
Provide SSL termination (HTTPS) for your websites, and expose one point of access (DNS) to your application.
It monitors the health of all your targets and only spreads the load to the healthy targets, so it basically does health check as well.
ELB is a managed Load Balancer by AWS, so AWS takes care of most of the stuff: you can also create your own but it's much more effort to maintain and integrate.
There are 3 main types of Load Balancer :
Application Load balancer - Layer 7 -> HTTP and HTTPS.
Network Load Balancer - Layer 4 .AKA. transport layer -> for high performance, TCP and UDP connections.
Classic Load Balancer (L7+4) -> It can only be used with EC2 classic instances. it is slowly retiring.
Auto-Scaling Group - ASG :
Normally if you have an app or system, it won't continually be under maximum load.
So if you're underestimating or overestimating your load, ,then there could be problems with cost and also, availability for customers/users, e.g. they might not be able to access the website because there might be a lot of latency because of too many users on the platform.
This is when ASG comes in; ASG automatically : -> Scales out when there is an increased load. -> Scales in when there is decreased load. -> It will also replace unhealthy targets/instances.
ASG and ELB work very well together because ASG can provide the instances and ELB can distribute the load between all of them.
ELB & ASG - Summary
High Availability vs Scalability ( Vertical and Horizontal ) vs Elasticity vs Agility in the cloud.
Elastic Load Balancers - ELB -> Distribute traffic across backend EC2 instances, can be Multi-AZ -> Support health checks -> 3 types : App LB ( HTTP/S - L7 ), Network LB ( TCP - L4), Classic LB (old)
Auto Scaling Groups ( ASG ) -> Implement Elasticity for your application, across multiple AZ -> Scale EC2 instances based on the demand on your system, replace unhealthy. -> Integrated with ELB
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