Section 8: High Availability and Scalability: ELB & ASG

Vertical Scalability

means increasing the size of the instance. (t2.micro to t2.large is an example of this)

There is a hardware limit on how much you can scale Vertically

True

Horizontal Scalability

means increasing the number of instances/systems for your applications.

Its easier to scale horizontal thanks to cloud offering services like

Amazon EC2

High Availability

means running your application/system in at least 2 data centers. (Run instances on same applications across multiple AZs)

Load Balancers

Are servers that forward traffic to multiple servers.

An Elastic Load balancer is a

Managed load balancer

ELB (Elastic Load Balancer)

AWS guarantees it will be working; takes care of upgrades, maintenance, highly available; integrated with many AWS services

Health Checks

crucial for load balancers. enables load balancers to know if instances it forwards traffic to are available to reply to requests.

4 Types of Load Balancers on AWS

-Classic Load Balancer (CLB) (NOT on EXAM)

-Application Load Balancer

-Network Load Balancer

-Gateway Load Balancer

Application Sec Group

Allows traffic only from Load Balancer

Application Load Balancer (ALB)(V2)

-Layer 7 only (HTTP)

-Support for HHTP/2 and Websocket

-Are a great fit for micro-services and container based applications

-has a port mapping feature to redirect to a dynamic port in ECS

-Fixed Hostname

ALB can route to multiple target groups

True

Network Load Balancer (NLB)

-Layer 4 Load Balancer that allows you to forward TCP and UDP traffic to your instances

-High performance, low latency

-Has one static IP per AZ and supports assigning Elastic IP

NLB target groups

-Can be EC2 Instances

-IP addresses must be private

-Application Load Balalncer

Health checks support

TCP, HTTP, and HTTPS protocols

Gateway Load Balancer (GWLB)

-Operates at level 3 network layer (IP packets)

-deploys, scales, and manages a fleet of 3rd party network virtual appliances in AWS

-Combines functions of a transparent network gateway, distributes traffic to virtual appliances, and uses the GENEVE protocol on port 6081

GLB Target Groups

-EC2 Instances

-IP addresses - must be private IPs

ELB stickiness

same client is always redirected to the same instance behind a load balancer. (works for classic application, and network load balancers.(done by the use of “cookies”)

Applicated-based cookies

-custom cookie (generated by the target)

-application cookie (generated by the load balancer)

-duration-based cookie (generated by the load balancer)