I have read that we can configure Auto Scaling to used CloudWatch metrics to scale in/or a pool of EC2 instances.
I'm curious to understand how ELB gets to know there is an EC2 instance added/removed to the Auto Scaling Group, so it does send workload to the newly added instance ? (or stop sending workload to the instance that has been removed?)
Regards,
Pascal
When you set them up, you associate the Auto Scaling group with the Elastic Load Balancer. The Auto Scaling Group then notifies the Elastic Load Balancer when instances are added or removed.
Related
Is there a way like assigning a specific tag for the EC2 instances to automatically attached to the load balancer on AWS?
I believe I had done that in the past but unable to find that option now.
Since you say you've done it in the past, I believe you're thinking of a feature offered by EC2 auto-scaling groups (ASGs). ASG is a capability of the EC2 infrastructure that scales machine counts up and down based on workload or maintains a set number of healthy instances always running (destroying and replacing failed instances). When an ASG is attached to a load balancer, the instances controlled by the ASG are automatically registered and deregistered from the balancer.
Amazon EC2 Auto Scaling integrates with Elastic Load Balancing to enable you to attach one or more load balancers to an existing Auto Scaling group. After you attach the load balancer, it automatically registers the instances in the group and distributes incoming traffic across the instances.
https://docs.aws.amazon.com/autoscaling/ec2/userguide/attach-load-balancer-asg.html
Per AWS documentation you can attach multiple Load Balancers to a Single Auto Scaling Group. I would think there would be 1:1 relationship between ELB and ASG. If ASG scales which ELB does it update- All.
How does this work, what is the use case.
Although you can attach, multiple load balancers to a single Auto Scaling group, its rarely being used, specially after AWS introduced Application Load Balancer (ALB) with support for Routing Rules (Domain and Path based) and attaching multiple SSL Certificates for a single load balancer features.
For example few scenarios where it was required previously (Before above mentioned new features were available.)
If you have multiple applications running inside an EC2 (Although it's not recommended) and needed their own SSL certificates, it'd be required to point to multiple load balancers.
If you have an Application Proxy Auto Scaling Group which points to backend services with their own SSL.
For different path and port mappings for internal applications in EC2 (Similar to Point 1)
Looking at the AWS documentation you can attach multiple Load Balancers to an ASG. When the ASG scales up all the Load Balancers will know about the new EC2 instances.
Auto Scaling integrates with Elastic Load Balancing to enable you to attach one or more load balancers to an existing Auto Scaling group. After you attach the load balancer, it automatically registers the instances in the group and distributes incoming traffic across the instances
link to above quote can be found here
In terms of scaling down if one of load balancers is reporting an instance as unhealthy then the instance will be considered unhealthy and eventually terminated.
If you configure your Auto Scaling group to determine health status using both EC2 status checks and Elastic Load Balancing health checks, Auto Scaling considers the instance unhealthy if it fails either the status checks or the health check. Note that if you attach multiple load balancers to an Auto Scaling group, all of them must report that the instance is healthy in order for Auto Scaling to consider the instance healthy. If one load balancer reports an instance as unhealthy, Auto Scaling replaces the instance, even if other load balancers report it as healthy
Link to above quote can be found here
I hope this makes things a bit clearer.
I am new to AWS. I would like to activate load balancing. I need to know that should I create multipl ec2 instance with the same files? Or only one instance is enough?. What will happen while heavy traffic?
AWS Elastic Load balancer (ELB) is for distributing traffic across multiple EC2 instances. You will be registering the instances with the ELB. Even when instances fail and new instances are added to ELB, the traffic is evenly distributed among the remaining active registered instances. Please see the documentation: AWS Elastic Load Balancing
If you have only one instance, ELB will send traffic only to that. But, what is the use of ELB then? It serves no purpose to have only 1.
If you need to scale out as the traffic increases, you need to use AWS Auto Scaling : AWS Auto Scaling
Using ELB for TCP protocol and AWS Auto Scaling I run into the following problem when scaling out.
three EC2 instances each with 2,000 connections
scaling out because that is my specified threshold
a new instance gets added by Auto Scaling
How can I stop now traffic going to the three EC2 instances which have too many connections?
Removing it from ELB will mean that it will get terminated after a maximum of 1h using connection draining. Bad: TCP connections will get closed.
Marking the EC2 instance as unhealthy using CloudWatch. Bad: Auto Scaling will detect and replace unhealthy instances
Detaching EC2 instance from Auto Scaling group manually via AWS CLI.
Bad: Detaching it from Auto Scaling will also remove it from ELB, see 1.
The only possible solution I can see here and I am not sure if it is feasible:
Using CloudWatch mark the EC2 instance as unhealthy. ELB will stop distributing traffic to it. At the same time update the EC2 health for Auto Scaling manually:
aws autoscaling set-instance-health --instance-id i-123abc45d –-health-status healthy
This should override the health in a way that ELB will continue to ignore the EC2 instance and AWS Auto Scaling will not try to replace the instance. Would that work or is there a better solution?
Hi. Does Amazon Elastic Load Balancing incorporate auto scaling?
That is: when the traffic drops to a low level from a high level, does it scale down?
Yes, it does.
According to the ELB product description,
Elastic Load Balancing automatically scales its request handling capacity in response to incoming application traffic.
Auto Scaling with Elastic Load Balancing
Let’s say that you want to make sure that the number of healthy Amazon EC2 instances behind an Elastic Load Balancer is never fewer than two. You can use Auto Scaling to set these conditions, and when Auto Scaling detects that a condition has been met, it automatically adds the requisite amount of Amazon EC2 instances to your Auto Scaling Group. Or, if you want to make sure that you add Amazon EC2 instances when latency of any one of your Amazon EC2 instances exceeds 4 seconds over any 15 minute period, you can set that condition, and Auto Scaling will take the appropriate action on your Amazon EC2 instances — even when running behind an Elastic Load Balancer. Auto Scaling works equally well for scaling Amazon EC2 instances whether you’re using Elastic Load Balancing or not.
As per the Auto Scaling feature description:
Auto Scaling allows you to scale your Amazon EC2 capacity up or down automatically according to conditions you define. With Auto Scaling, you can ensure that the number of Amazon EC2 instances you’re using increases seamlessly during demand spikes to maintain performance, and decreases automatically during demand lulls to minimize costs. Auto Scaling is particularly well suited for applications that experience hourly, daily, or weekly variability in usage.
Features of Auto Scaling
Scale out Amazon EC2 instances seamlessly and automatically when demand increases.
Shed unneeded Amazon EC2 instances automatically and save money when demand subsides.
Scale dynamically based on your Amazon CloudWatch metrics, or predictably according to a schedule that you define.
Yes, You can attach Amazon Auto Scaling with Amazon Elastic Load Balancing. In event an Load increases, new EC2 can be launched by Amazon Auto Scaling and it will seamlessly get attached to Amazon ELB. In event traffic reduces, Auto scaling will terminate EC2 instances which will be deregistered from ELB. This scheme works both in Amazon Classic cloud and Amazon VPC.