AWS Fundamentals: ELB + ASG Flashcards
What is vertical scalability?
Increasing the size of an instance, e.g., from t2.micro to t2.large.
What is horizontal scalability (elasticity)?
Increasing the number of instances in a system.
What is high availability?
Running an application in at least two Availability Zones to survive failures.
What AWS features support horizontal scaling and high availability?
Auto Scaling Groups and Load Balancers across multiple AZs.
What does an Elastic Load Balancer (ELB) do?
Distributes traffic to multiple EC2 instances.
What are the benefits of using a load balancer?
Load spreading, health checks, SSL termination, DNS endpoint, stickiness, high availability.
What is the advantage of a managed ELB?
AWS handles uptime, maintenance, scaling, and integration with other services.
What is a health check in ELB?
It monitors instance health using a port and route, expecting a 200 OK.
What are the 4 types of AWS load balancers?
CLB, ALB, NLB, GWLB.
What protocols does CLB support?
HTTP, HTTPS, TCP, SSL.
What is the primary use of ALB?
HTTP/HTTPS Layer 7 load balancing, routing, container support.
How does ALB support routing?
Based on URL path, hostname, headers, or query strings.
What can ALB target groups contain?
EC2, ECS tasks, Lambda functions, IP addresses.
How does ALB expose client IPs?
Via the X-Forwarded-For header.
What is a Network Load Balancer (NLB)?
Layer 4 load balancer for TCP/UDP traffic with low latency.
What feature makes NLB suitable for whitelisting?
Supports static and Elastic IPs.
What is a Gateway Load Balancer (GWLB)?
Handles traffic for third-party appliances like firewalls at Layer 3.
How does sticky session work in ELB?
Client is always redirected to the same backend instance using cookies.
What are the cookie names for sticky sessions?
AWSALBAPP (application), AWSALB (duration), AWSELB (CLB).
What is Cross-Zone Load Balancing?
Distributes requests evenly across all AZs.
What is the default state of Cross-Zone Load Balancing?
Enabled for ALB, disabled for NLB & GWLB (can incur costs).
What is SSL/TLS used for?
Encrypting in-flight traffic between client and load balancer.
How are SSL certs managed in AWS?
Using AWS Certificate Manager (ACM).
What is Server Name Indication (SNI)?
Allows multiple SSL certs on a single listener.
Which load balancers support SNI?
ALB, NLB, and CloudFront.
How many SSL certs does CLB support?
Only one. Multiple CLBs needed for multiple certs.
What is connection draining?
Allows in-flight requests to complete before instance termination.
What is the ASG goal?
Maintain instance count, scale based on load, auto-register to ELB, replace unhealthy instances.
What components make up an ASG launch template?
AMI, instance type, user data, volumes, security groups, key pair, IAM role.
What scaling can be triggered by CloudWatch alarms?
Scale-out or scale-in actions.
What is predictive scaling?
Forecasts future load and pre-scales instances.
What metrics can be used for scaling?
CPUUtilization, RequestCountPerTarget, Network In/Out, custom metrics.
What is ASG cooldown period?
Delay after scaling to stabilize metrics (default 300 seconds).
What is ASG Instance Refresh?
Recreates instances using a new launch template.
