Section 8: High Availability and Scalability, ELB & ASG

Question 1

What are the two types of scalability?

Answer 1

Horizontal Scaling and Vertical Scaling

Question 2

Define Vertical Scalability and its use cases

Answer 2

Vertical scaling is increasing / decreasing the instance size/power (from regular EC2 to baremetal, for example).
Use Cases: non-distributed systems, like DBs, and when you have a hardware limit for scaling

Question 3

Define Horizontal Scalability and its use cases

Answer 3

Horizontal Scaling (elasticity) is increasing / decreasing the number of instances.
Use Cases: Distributed systems (web apps, modern apps) & ASGs / load balancers

Question 4

High availability and ____ go hand in hand

Answer 4

Horizontal Scaling (for running instances for the same app, across multiple AZs

Question 5

What is the goal of High availability?

Answer 5

To survive an unexpected data center loss

Question 6

What is a load balancer?

Answer 6

Load balancers are physical / virtual servers that forward traffic to multiple servers (EC2 instances) downstream. They do not need to be internet facing.

Question 7

What are some reasons to use a load balancer? 5 things.

Answer 7

1) Spread load across multiple downstream instances
2) Expose a signle point of access (DNS) to your application
3) Easily handle failure of downstream instances
4) Separate private and public traffic
5) regular health checks and SSL termination (HTTPS) for websites

Question 8

What are the four (4) types of Elastic Load Balancers (ELBs)?

Answer 8

1) ALB (application load balancer)
2) Network Load Balancer (NLB)
3) Gateway Load Balancer (GLB)
4) Classic Load Balancer (CLB)

Question 9

When should you use an ALB?

Answer 9

ALBs are best suited for load balancing of HTTP, Websocket & HTTPS traffic. They provide a static DNS name but not a static IP.

Question 10

What level do ALB’s perform health checks

Answer 10

ALBs perform health checks at the target group level. Target groups include EC2 instances, Lambda Functions, IP addresses, and more.

Question 11

What are two ALB use cases

Answer 11

1) Micro Services
2) Container based applications (docker, amazon ECS)

Question 12

When should you use an NLB?

Answer 12

NLBs are suited for load balancing of TCP (transmission control protocol) traffic where extreme performance is required

Question 13

What are three (3) main qualities of NLBs?

Answer 13

1) provides Static DNS name and Static IP
2) Can support millions of requests per second and ultra-low latencies compared to ALB
3) NLBs are meant for extreme performance, TCP and UDP traffic

Question 14

When should you use a GLB?

Answer 14

A GLB should be used when network traffic must be inspected before sending it to an application

Question 15

What are some use cases for GLB?

Answer 15

1) firewalls, intrusion detection, preventative systems
2) deploying, scaling and managing a fleet of 3rd party network virtual appliances

Question 16

What re some use cases for CLB (Classic load balancer?)

Answer 16

None. CLBs are deprecated.

Question 17

What are Sticky Sessions (session affinity) and what do they do?

Answer 17

Sticky Sessions bind a user’s session to a specific EC2 instance or target (ALB).
Sticky Sessions ensure all requests from the user will be sent to the same place to make sure the user doesn’t lose session data

Question 18

What are two cons of Sticky Sessions?

Answer 18

1) If you aren’t getting connected to a specific EC2 instance, you might need to disable Sticky Sessions
2) Enabling stickiness can bring imbalance to the load

Question 19

Stickiness is achieved by using two types of cookies. What are these cookies called?

Answer 19

1) Application based cookies
2) Duration based cookies

Question 20

What are Application Based Cookies?

Answer 20

Application Based Cookies are generated by an an application or a load balancer, named specifically for each target group

Question 21

What are Duration Based Cookies?

Answer 21

Cookie generated by a load balancer, named AWSALB for ALBs, AWSELB for CLB

Question 22

What is Cross Zone Load Balancing?

Answer 22

When a load balancer balances a load evenly across targets in Multiple AZs

Question 23

What if Cross Zone Load Balancing is not enabled?

Answer 23

Requests will be distributed in the instances of the load balances, but no guarantee the loads will be balanced across AZs. Cross Zone is always on for ALBs

Question 24

What if Cross Zone Load Balancing is not enabled?

Answer 24

Requests will be distributed in the instances of the load balances, but no guarantee the loads will be balanced across AZs

Question 25

What Does an SSL (Secure Socket Layer) / TSL (Transport Layer Security) certificate do?

Answer 25

SSL certificates allow traffic between your clients and your load balancer to be encrypted in transit (in-flight encryption)

Question 26

How does SSL / LS work with load balancers?

Answer 26

1) User connects to load balancer via HTTPs 2) Load Balancer verifies if network is encrypted 3) Load Balancer navigates encrypted traffic to EC2 Instance

Question 27

What is SNI (Server Name Indication) and what does it do?

Answer 27

SNI allows users to load multiple SSL certificates into one or different web servers via load balancers. Only applicable to ALB / NLB / CloudFront, and all traffic is HTTPS

Question 28

What are the four (4) main goals of an ASG (Auto Scaling Group)?

Answer 28

1) Scale out (add EC2 instances) to match increased load 2) Scale in (remove EC2 instances) to match decreased load 3) ensure a minimum and maximum amount of machines running 4) Automatically register new instances to a load balancer

Question 29

Can you assign IAM roles to an ASG?

Answer 29

Yes. IAM roles attached to an ASG will get assigned to the correlative EC2 instances

Question 30

How much does an ASG cost?

Answer 30

ASG's are free, you only pay for the underlying resources launched in the ASG

Question 31

What happens if an instance in an ASG fails a health check?

Answer 31

the ASG will automatically create a new instance as a replacement

Question 32

What are the attributes of an ASG?

Answer 32

1) Launch configuration (resources to be used, SGs, Storage, etc.) 2) Min / Max size, Initia; / desired capacity 3) Network, load balancer & subnet information 4) Scaling policies (what triggers a scale in or scale out)

Question 33

What are the two types of Automatic Scaling policies for an ASG?

Answer 33

1) Dynamic scaling policies 2) Predictive scaling policies

Question 34

What are the three types of Dynamic Scaling Policies for an Automatic Scaling ASG?

Answer 34

1) Target Tracking Scaling 2) Simple / Step Scaling 3) Schedule Actions

Question 35

What is Target Tracking Scaling for an ASG?

Answer 35

Sets an average ASG CPU preference, and is the most simple scaling policy to set up / use

Question 36

What is Simple / Step Scaling for an ASG?

Answer 36

Simple / Step scaling utilizes CloudWatch alarms to configure scaling steps. For example: when a CloudWatch alarm is triggered, then a preset action is performed (like add or subtract a certain amount of EC2s)

Question 37

What are Scheduled Action scaling policies for an ASG?

Answer 37

Scheduled Action policies are used to anticipate scaling based on known usage patterns. This proactive scaling helps to scale during desired time windows For example: People come to your site to stream the new show every Friday at 5 pm, so you preset EC2 scaling.

Question 38

What are four (4) good metrics to base your ASG scaling on?

Answer 38

1) CPU utilization: average CPU usage across instances 2) Request count per target: ensures number of requests per EC2 instances is stable 3) Average in / out operations: for network bound apps 4) Custom metrics pushed using CloudWatch

Question 39

What is Manual Scaling for an ASG?

Answer 39

Manual Scaling for an ASG is when you specify maximum and minimum ASG capacity

Question 40

What is an ASG Scaling Cooldown period and why is it beneficial?

Answer 40

An ASG scaling cooldown period is a default 300 second waiting period that prevents ASGs from launching or terminating additional instances before the effects of previous activities are visible.

Question 41

What is the default ASG Termination Policy?

Answer 41

The default termination policy finds the AZ which has the most instances. If there are are multiple instances in the AZ to choose from, it will delete the one with the oldest launch configuration

Question 42

By default, how do ASGs manage EC2 instances in an Az?

Answer 42

By default, ASGs try to balance the number of instances across an AZ