I have an on-premises load balancer that I wish to use to distribute traffic on EC2s in an Autoscaling group(ASG).
When AWS's Elastic Load Balancer(ELB) registers an ASG as a target, during a scale-out,new instances are automatically registered to ELB to route traffic to.
Can the same functionality be achieved in any way with an on-prem load balancer?
There is in-built integration between Amazon EC2 Auto-Scaling and Elastic Load Balancers. The Auto Scaling systems knows how to modify Target Groups to add/remove instances. However, it has no knowledge about your on-premises load balancer.
You could use Amazon EC2 Auto Scaling lifecycle hooks to trigger additional code (that you write) to add/remove the instances to your own load balancer, but that would require an AWS Lambda function to communicate with the on-premises load balancer to update the configuration.
If you wanted to get the IPs of your target group you can do that do with an API call, and put that into your LB, but I think you may as well proxy calls from your LB to an ELB sitting on AWS which does the actual LoadBalancing. IMO there is way too much work and a lot could go wrong if you were to try and re-implement ELB features using Lambda functions.
I'm a little too confused on the terms and its usage. Can you please help me understand how are these used with Load Balancers?
I referred the aws-doc in vain for this :(
Target groups are just a group of Ec2 instances. Target groups are closely associated with ELB and not ASG.
ELB -> TG - > Group of Instances
We can just use ELB and Target groups to route requests to EC2 instances. With this setup, there is no autoscaling which means instances cannot be added or removed when your load increases/decreases.
ELB -> TG - > ASG -> Group of Instances
If you want autoscaling, you can attach a TG to ASG which in turn gets associated to ELB. Now with this setup, you get request routing and autoscaling together. Real world usecases follow this pattern. If you detach the target group from the Auto Scaling group, the instances are automatically deregistered from the target group
Hope this helps.
What is a target group?
A target group contains EC2 instances to which a load balancer distributes workload.
A load balancer paired with a target group does NOT yet have auto scaling capability.
What is an Auto Scaling Group (ASG)?
This is where auto scaling comes in. An auto scaling group (ASG) can be attached to a load balancer.
We can attach auto scaling rules to an ASG. Then, when thresholds are met (e.g. CPU utilization), the number of instances will be adjusted programatically.
How to attach an ASG to a load balancer?
For Classic load balancer, link ASG with the load balancer directly
For Application load balancer, link ASG with the target group (which itself is attached to the load balancer)
Auto Scaling Group is just a group of identical instances that AWS can scale out (add a new one) or in (remove) automatically based on some configurations you've specified. You use this to ensure at any point in time, there is the specific number of instances running your application, and when a threshold is reached (like CPU utilization), it scales up or down.
Target Group is a way of getting network traffic routed via specified protocols and ports to specified instances. It's basically load balancing on a port level. This is used mostly to allow accessing many applications running on different ports but the same instance.
Then there are the classical Load Balancers where network traffic is routed between instances.
The doc you referred to is about attaching load balancers (either classical or target group) to an auto-scaling group. This is done so scaling instances can be auto-managed (by the auto scaling group) while still having network traffic routed to these instances based on the load balancer.
Target groups
They listen to HTTP/S request from a Load Balancer
Are the Load Balancer's targets which will be available to handle an HTTP/S request from any kind of clients (Browser, Mobile, Lambda, Etc). A target has a specific purpose like Mobile API processing, Web App processing, Etc. Further, these target groups could contain instances with any kind of characteristics.
AWS Docs
Each target group is used to route requests to one or more registered targets. When you create each listener rule, you specify a target group and conditions. When a rule condition is met, traffic is forwarded to the corresponding target group. You can create different target groups for different types of requests. For example, create one target group for general requests and other target groups for requests to the microservices for your application. Reference
So, a Target Group provides a set of instances to process specific HTTP/S requests.
AutoScaling groups
They are a set of instances who were started up to handle a specific workload, i.e: HTTP requests, SQS' message, Jobs to process any kind of tasks, Etc.
On this side, these groups are a set of instances who were started up by a metric which exceeded a specific threshold and triggered an alarm. The main difference is that Autoscaling groups' instances are temporary and they are available to process anything, from HTTP/S requests until SQS' messages. Further, the instances here are temporary and can be terminated at any time according to the configured metric. Likewise , the Autoscaling groups share the same characteristics because the follow something called Launch Configuration.
AWS Docs
An Auto Scaling group contains a collection of EC2 instances that share similar characteristics and are treated as a logical grouping for the purposes of instance scaling and management. For example, if a single application operates across multiple instances, you might want to increase the number of instances in that group to improve the performance of the application or decrease the number of instances to reduce costs when demand is low. Reference
So, an Autoscaling group not only will be able to process HTTP/S requests but also can process backend stuff, like Jobs to send emails, jobs to process tasks, Etc.
As I understand it, Target Groups is a connection between ELB and EC2 instances. Some kind of a service discovery rules. This layer allows to Target Groups for ECS Services for instance when it's possible to have more than one container per instance.
Auto-Scaling Groups is an abstraction for aggregation of EC2 metrics and taking some actions based on that data.
Also, bear in mind, that the possibility of attaching of Auto-Scaling Groups to ELB comes from the previous generation of ELBs. You may compare the first generation and the second one in the CloudFormation docs.
I'm thinking of using cloud formation as a means of blue-green deployment.
Part of it is putting instances of the Autoscaling group instances on stand by.
Is that possible?
Amazon EC2 Auto Scaling groups are responsible for launching and terminating Amazon EC2 instances. Note that instances are launched as new instances -- they are not kept on standby.
You can certainly do blue-green deployments by using two separate CloudFormation stacks, each with their own Auto Scaling group and, presumably, Elastic Load Balancer.
Both Auto Scaling groups would be 'operating', but not necessarily receiving traffic. You would then need some mechanism to 'switch' between the blue/green groups, such as changing a DNS entry in Route 53 to point to the different Load Balancer.
Adding to John's Answer, On route 53 you can use weighted load balancing to route traffic. It allows you to route percentage traffic to the setups.
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
In the above architecture (source: http://media.amazonwebservices.com/AWS_Web_Hosting_Best_Practices.pdf), The application server cluster belong to an autoscaling group. But is load balanced by a software loadbalancer (like nginx or HAProxy). My question is if the how the nodes in autoscaling group registers itself automatically with the loadbalancer(As I understand Elastic loadbalancer has this capability builtinm which may not be case for nginx or HAProxy)
When you create Autoscaling group in AWS, you connect it with launch configuration which is responsible for launching new instances of the specific image, so each instance is automatically assigned to autoscaling group.
In the next step, you register your load balancer with your autoscaling group, so load balancer can use any of the instances that belongs to the group.
Please check this tutorial http://docs.aws.amazon.com/AutoScaling/latest/DeveloperGuide/as-register-lbs-with-asg.html
Zoran
There's a great blog post on how to do this using PHP app.
http://www.kloppmagic.ca/auto-scaling-with-haproxy/
Of course you could use other tools like consul and service discovery baked into your image.