7. ELB + ASG

Question 1

What is an ALB?

Answer 1

Application Load Balancer

• Provides Layer 7 load balancing to multiple HTTP applications across machines (target groups)
• Provides balancing to multiple applications on the same machine (containers)
• Supports redirects (from HTTP to HTTPS)
• Can route based on URL path, URL hostname, and Query String
• Has a port mapping feature to redirect to a dynamic port in ECS
• Cross-zone load balancing: always on (can’t be disabled), free for inter-AZ
• Supports SNI for multiple listeners with multiple SSL certificates

Question 2

What is an NLB?

Answer 2

Network Load Balancer

• Layer 4 (TCP and UDP)
• Used for extreme performance, TCP or UDP traffic
• Cross-zone load balancing: disabled by default, you pay for inter-AZ
• Supports SNI for multiple listeners with multiple SSL certificates

Question 3

What is vertical scalability?

Answer 3

Increasing the size of your instance

Question 4

What is horizontal scalability?

Answer 4

Increasing the number of instances / systems for your application

Question 5

What is Load Balancer Stickiness?

Answer 5

The same client is always redirected to the same instance behind a local load balancer
- the “cookie” used for stickiness has an expiration date you can control

Question 6

What is SNI?

Answer 6

Server Name Indication

- solved the problem of loading multiple SSL certificates onto one web server (to serve multiple websites)

Question 7

What is Connection Draining?

Answer 7

Allows time to complete “in-flight requests” while the instance is de-registering or unhealthy

• stops sending new requests to the instance which is de-registering
• between 1 to 3600 seconds (default is 300 sec)
• set to low value if requests are short
• can be disabled

Question 8

Where would you go to analyze incoming requests for latencies and client’s IP address patterns for an ALB?

Answer 8

ALB access logs

Question 9

True or False: A Load Balancer can target EC2 instances only within an AWS Region.

Answer 9

True

Question 10

What Load Balancer HTTP Error means it is at capacity or has no registered target?

Answer 10

HTTP 503

HTTP 503 indicates ‘Service unavailable’ error. This error in ALB is an indicator of the target groups for the load balancer having no registered targets.

Question 11

Load Balancer HTTP Error indicating internal server error

Answer 11

HTTP 500

There are several reasons for their error: A client submitted a request without an HTTP protocol, and the load balancer was unable to generate a redirect URL, there was an error executing the web ACL rules.

Question 12

What is CloudFront?

Answer 12

• Improves read performance, content is cached at edge
• Global Edge Network / Content Delivery Network
• Files are cached for a TTL (maybe a day)
• Great for static content that must be available everywhere

Question 13

What is CNAME used for?

Answer 13

• hostname to hostname

- only for NON-ROOT domain (ex: mail.google.com)

Question 14

What is ALIAS used for

Answer 14

• hostname to AWS resource

- works for ROOT and NON-ROOT domain (ex: google.com and mail.google.com)

Question 15

ACM can be attached to which AWS resources?

Answer 15

Amazon Certificate Manager

1. Elastic Load Balancer
2. CloudFront
3. API Gateway
4. Elastic Beanstalk (through ELB)

Question 16

Which ELB supports assigning an Elastic IP?

Answer 16

Network Load Balancer (NLB)

This is helpful for whitelisting a specific IP

Question 17

Which ELB supports stickiness?

Answer 17

ALB

Question 18

Which ELB(s) have one static IP per AZ?

Answer 18

NLB

Question 19

What is an Elastic IP?

Answer 19

A fixed public IP address

Question 20

What is the error a Load Balancer generates when the target groups for the load balancer have no registered targets?

Answer 20

HTTP 503: Service unavailable