Configuring Elastic Load Balancing

The Elastic Load Balancer (ELB) works within a single AWS region. You can scale both horizontally (adding more EC2 instances) and vertically (increasing EC2 instance size) within AWS, but it's best practice to scale horizontally. It can, however, load balance across several instances in multiple availability zones. If you don't want to load balance instances across multiple availability zones, then you can also disable it. If we want to load balance the instances across multiple regions, then we have to use Route 53 (instead of an ELB). ELB continuously checks the health of the instances, and only routes traffic to healthy instances. The health check frequency and the URL parameters are configurable.

If a healthy instance comes online, then the ELB recognizes the instance and routes traffic to it. ELB can be used to implement high-availability application architectures. If we use Route 53 with ELB, we can enable failover to a different region. ELB can also be configured with autoscaling, thereby enabling load balancing across new instances created by auto-scaling groups.

ELB can work with instances in EC2-Classic and VPC. There are two types of load balancers we can create internal or internet facing. We can't create internal load balancer without VPC. We can create both internal and internet facing load balancers within VPC. You can also enable sticky sessions on ELB using either application generated cookies or ELB generated cookies. In addition, you can assign security groups to ELBs. If you don't assign any security group while creating the ELB in VPC, it uses the default security group of the VPC. SSL termination is also supported in ELB, using this obviates the need to install SSL certificate on each and every EC2 instance.

$ aws elb create-load-balancer 
--load-balancer-name [LoanBalancerName] 
--listeners [Listeners]
--subnets [SubnetIds] 
--security-groups [SecurityGroups]

$ aws elb create-load-balancer
--load-balancer-name WebLoadBalancer
--listeners Protocol=HTTP,LoadBalancerPort=80,InstanceProtocol=HTTP,InstancePort=8080 
--subnets subnet-aed11acb 
--security-groups sg-c6b873a3

$ aws elb configure-health-check 
--load-balancer-name [LoanBalancerName] 
--health-check [HealthCheckup]

$ aws elb configure-health-check 
--load-balancer-name WebLoadBalancer
--health-check Target=HTTP:8080/index.html,Interval=30,UnhealthyThreshold=2,HealthyThreshold=2,Timeout=3 

$ aws elb register-instances-with-load-balancer
--load-balancer-name [LoanBalancerName] 
--instances [Instances]

$ aws elb register-instances-with-load-balancer 
--load-balancer-name WebLoadBalancer 
--instances i-d3ff2c1e i-2e7dace3