AWS ELB Exam Preparation

Elastic Load Balancer – Automatically distributes incoming application traffic across multiple Amazon instances(EC2). It enables customers to achieve even greater fault tolerance in their applications, seamlessly providing the amount of load balancing capacity needed in response to incoming application traffic

  • Distributes incoming traffic across multiple instances/targets.
  • Types
    • Network LB
      • Operates at layer-4, listener level (TCP/ip).
      • Network Load Balancer preserves the source IP
    • Application LB
      • Operates at layer 7, HTTP/HTTPS
    • Classic LB
      • Basic load balancing service.
  • Health checks can be done, to divert traffic away from unhealthy instances.
  • Components,
    • Response Timeout – Amount of time to wait for a response.
    • Interval – Time between the 2 health checks
    • Unhealthy Threshold – Number of consecutive health checks failure, and then declare EC2 failed health check.
    • Healthy Threshold – How many consecutive health check it needs to pass before considering healthy.
  • ELB will always have DNS names and not IP.
  • DNS will be used for hitting the ec2 servers, we can use Alias or CNAME @ Route53 to hit this url.

Exam Tips:(A very important Service/topic for exam)

  • There can be more than 1 application behind a single elb and each application can have multiple ec2.
  • Application Load Balancer is best suited for load balancing of HTTP and HTTPS traffic and provides advanced request routing targeted at the delivery of modern application architectures, including microservices and containers.
  • Network Load Balancer is best suited for load balancing of TCP traffic where extreme performance is required.
  • Ec2 instance will always see ELB IP address rather than original requestor’s IP, Configure X-forwarded to see client IP.
  • The controller service monitors the load balancers, adding and removing load balancers as needed and verifying that the load balancers are functioning properly.
  • SSL certificate will have to be installed at ELB.
  • ELB always makes 2 connections one for Instance and other with Client.
  • Elastic Load Balancing health check may be a ping, a connection attempt, or a page that is checked.
  • When connection draining is enabled, the load balancer will stop sending requests to a deregistered or unhealthy instance.


  • Try creating,
    • Network Load Balancer (you can expect 2 – 3 questions on this).
    • Application Load balancer (multiple questions).