Auto Scaling helps to automatically increase the number of EC2 instances when the user demand goes up, and decrease the number of EC2 instances when demand goes down
ELB service helps to distribute the incoming web traffic (called the load) automatically among all the running EC2 instances
ELB uses load balancers to monitor traffic and handle requests that come through the Internet.
Auto Scaling dynamically adds and removes EC2 instances, while Elastic Load Balancing manages incoming requests by optimally routing traffic so that no one instance is overwhelmed
Using ELB & Auto Scaling
makes it easy to route traffic across a dynamically changing fleet of EC2 instances
load balancer acts as a single point of contact for all incoming traffic to the instances in an Auto Scaling group.
Attaching/Detaching ELB with Auto Scaling Group
Auto Scaling integrates with Elastic Load Balancing and enables to attach one or more load balancers to an existing Auto Scaling group.
After the ELB is attached, it automatically registers the instances in the group and distributes incoming traffic across the instances
ELB registers the EC2 instance with the ELB using its IP address and routes requests to the primary IP address of the primary interface (eth0) of the instance.
When ELB is detached, it enters the Removing state while deregistering the instances in the group.
If connection draining is enabled, ELB waits for in-flight requests to complete before deregistering the instances.
Instances remain running after they are deregistered from the ELB
Auto Scaling adds instances to the load balancer as they are launched, but this can be suspended. Instances launched during the suspension period are not added to load balancer, after resumption, and must be registered manually.
High Availability & Redundancy
Auto Scaling can span across multiple AZs, within the same region
When one AZ becomes unhealthy or unavailable, Auto Scaling launches new instances in an unaffected AZ
When the unhealthy AZs recovers, Auto Scaling redistributes the traffic across all the healthy AZs
Elastic Load balancer can be setup to distribute incoming requests across EC2 instances in a single AZ or multiple AZs within a region
It is recommended to take advantage of the safety and reliability of geographic redundancy by using Auto Scaling & ELB by spanning Auto Scaling groups across multiple AZs within a region and then setting up ELB to distribute incoming traffic across those AZs.
Incoming traffic is load balanced equally across all the AZs enabled for ELB
Auto Scaling group determines the health state of each instance by periodically checking the results of EC2 instance status checks
Auto Scaling marks the instance as unhealthy and replaces the instance, if the instance fails the EC2 instance status check
ELB also performs health checks on the EC2 instances that are registered with the it for e.g. if the application is available by pinging and health check page
Auto Scaling, by default, does not replace the instance, if the ELB health check fails
ELB health check with the instances should be used to ensure that traffic is routed only to the healthy instances
After a load balancer is registered with an Auto Scaling group, it can be configured to use the results of the Elastic Load Balancing health check in addition to the EC2 instance status checks to determine the health of the EC2 instances in your Auto Scaling group.
Elastic Load Balancing sends data about the load balancers and EC2 instances to Amazon CloudWatch. CloudWatch collects data about the performance of your resources and presents it as metrics.
After registering one or more load balancers with the Auto Scaling group, Auto Scaling group can be configured to use ELB metrics (such as request latency or request count) to scale the application automatically
Sample Exam Questions
Questions are collected from Internet and the answers are marked as per my knowledge and understanding (which might differ with yours).
AWS services are updated everyday and both the answers and questions might be outdated soon, so research accordingly.
AWS exam questions are not updated to keep up the pace with AWS updates, so even if the underlying feature has changed the question might not be updated
Open to further feedback, discussion and correction.
A company is building a two-tier web application to serve dynamic transaction-based content. The data tier is leveraging an Online Transactional Processing (OLTP) database. What services should you leverage to enable an elastic and scalable web tier?
Elastic Load Balancing, Amazon EC2, and Auto Scaling
Elastic Load Balancing, Amazon RDS with Multi-AZ, and Amazon S3
Amazon RDS with Multi-AZ and Auto Scaling
Amazon EC2, Amazon DynamoDB, and Amazon S3
A user has configured ELB with Auto Scaling. The user suspended the Auto Scaling AddToLoadBalancer, which adds instances to the load balancer. process for a while. What will happen to the instances launched during the suspension period?
The instances will not be registered with ELB and the user has to manually register when the process is resumed
The instances will be registered with ELB only once the process has resumed
Auto Scaling will not launch the instance during this period due to process suspension
It is not possible to suspend only the AddToLoadBalancer process
You have an Auto Scaling group associated with an Elastic Load Balancer (ELB). You have noticed that instances launched via the Auto Scaling group are being marked unhealthy due to an ELB health check, but these unhealthy instances are not being terminated. What do you need to do to ensure trial instances marked unhealthy by the ELB will be terminated and replaced?
Change the thresholds set on the Auto Scaling group health check
Add an Elastic Load Balancing health check to your Auto Scaling group
Increase the value for the Health check interval set on the Elastic Load Balancer
Change the health check set on the Elastic Load Balancer to use TCP rather than HTTP checks