Load Balancers / High Availability 101 Flashcards
What does TCP stand for?
Transmission Control Protocol
What does a Network Load Balancer do?
- best-suited for load balancing TCP traffic where extreme performance is required
- capable of handling millions of requests per second, while maintaining ultra-low latencies
At what layer do ALBs operate?
Layer 7
At what layer do NLBs operate?
Layer 4
What will your load balancer return if your application is having issues?
A 504 Gateway timeout
What is the purpose of an X-Forwarded-For header?
If you need the IPv4 address of your end user
What are the two report out statuses for ELBs?
- InService
- OutofService
Do you get an IP address for your Load Balancers?
No; Load Balancers have their own DNS name
What do Sticky Sessions do?
They allow you to bind a user’s session to a specific EC2 instance, so that all requests from the user during the session are sent to the same instance.
Suppose you notice that all requests from a user are going to a single EC2 instance from an ELB. What might be causing this?
Sticky sessions are probably enabled
Suppose Route53 is routing traffic evenly between two different availability zones, each of which has an ELB. The first AZ’s ELB is load-balancing 4 different EC2 instances, and the second AZ’s ELB is load-balancing just 1 EC2 instance. You want can you do to ensure that all 5 EC2 instances receive the same amount of traffic?
Turn on Cross Zone Load Balancing
Suppose Route53 is routing all traffic to US-EAST-1A, where an ELB is load-balancing traffic between 4 different EC2 instances. For high availability, you bring up another EC2 instance in US-EAST-1B. How can you get the load balancer in US-EAST-1A to start sending traffic to the new EC2 instance?
Enable Cross Zone Load Balancing
Suppose Route53 is routing all traffic to US-EAST-1A, where an ELB is load-balancing traffic between 4 different EC2 instances. You bring up another 2 EC2 instances in US-EAST-1B, your goal is to send traffic to www.myurl.com to one of the instances in US-EAST-1A, and traffic to www.myurl.com/images/ to one of the instances in US-EAST-1B. How can this be accomplished without creating new load balancers or changing anything in Route53?
Enable Path Patterns
Suppose you are using a load balancer, but some of your user’s requests store information locally on the target EC2 instance, so you’ll need to ensure that your users stick to the same EC2 instance. How can you accomplish this?
Turn on Sticky Sessions
What do Path Patterns do?
Path Patterns allow you to direct traffic to different EC2 instances based on the URL contained in the request
