Auto Scaling with ELB integration in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Architecture

intermediate

How does an Auto Scaling group interact with an Elastic Load Balancer?

When you attach an Auto Scaling group to an Elastic Load Balancer (ELB), what happens to the instances launched by the Auto Scaling group?

A The instances must be manually registered with the ELB after launch to receive traffic.

B The instances are automatically registered with the ELB and receive traffic based on health checks.

C The ELB only routes traffic to instances outside the Auto Scaling group.

D The Auto Scaling group disables ELB health checks and uses its own only.

💡 Hint

Think about how ELB and Auto Scaling work together to distribute traffic.

When an Auto Scaling group is attached to an ELB, instances launched by the group are automatically registered with the ELB. The ELB then routes traffic only to healthy instances based on health checks.

❓ service_behavior

intermediate

What happens when an instance fails ELB health checks in an Auto Scaling group?

If an instance in an Auto Scaling group attached to an ELB fails the ELB health checks, what is the expected behavior?

A The instance remains running but is removed from the ELB's routing until healthy again.

B The Auto Scaling group disables the ELB health checks and relies on EC2 status checks.

C The ELB ignores the health check failure and continues routing traffic to the instance.

D The instance is immediately terminated and replaced by the Auto Scaling group.

💡 Hint

Consider how ELB and Auto Scaling handle instance health separately.

When an instance fails ELB health checks, the ELB stops sending traffic to it but the instance remains running. The Auto Scaling group may terminate it only if EC2 health checks fail or scaling policies trigger.

❓ security

advanced

Which security group configuration allows Auto Scaling instances to register with an ELB?

You have an Auto Scaling group and an ELB in the same VPC. Which security group rule is required to allow the ELB to send traffic to the instances?

A Allow inbound traffic on all ports from the instances' security group in the ELB's security group.

B Allow inbound traffic on the ELB listener port from 0.0.0.0/0 in the instances' security group.

C Allow outbound traffic on all ports from the instances' security group to 0.0.0.0/0.

D Allow inbound traffic on the ELB listener port from the ELB's security group in the instances' security group.

💡 Hint

Think about how security groups reference each other for traffic control.

The instances' security group must allow inbound traffic on the ELB listener port from the ELB's security group. This allows the ELB to send traffic securely to instances.

❓ Configuration

advanced

What is the effect of setting ELB health check grace period in Auto Scaling?

In an Auto Scaling group attached to an ELB, what does setting a health check grace period do?

A It forces immediate termination of instances failing ELB health checks during the grace period.

B It disables ELB health checks permanently for all instances in the group.

C It delays the start of ELB health checks on new instances to allow them to initialize.

D It sets the timeout for ELB health checks to wait for a response from instances.

💡 Hint

Consider why new instances might need time before health checks start.

The health check grace period delays ELB health checks on new instances to give them time to start up and become healthy before being evaluated.

✅ Best Practice

expert

How to ensure zero downtime during Auto Scaling group updates with ELB?

You want to update the launch configuration of an Auto Scaling group attached to an ELB without causing downtime. Which approach ensures zero downtime?

A Create a new Auto Scaling group with the updated launch configuration and gradually shift traffic using ELB target group deregistration delay.

B Update the launch configuration and immediately terminate all instances to force replacement.

C Detach the ELB from the Auto Scaling group during update and reattach after all instances are replaced.

D Manually deregister instances from the ELB before terminating them to avoid traffic loss.

💡 Hint

Think about how to replace instances gradually without dropping traffic.

Creating a new Auto Scaling group with the updated launch configuration and shifting traffic gradually using ELB's deregistration delay allows zero downtime updates.