ELB - Elastic Load Balancer
It is a managed service by AWS (Scalability and Availablity is managed by AWS). Mainly it used for distributing traffic between instances. Once if the instance is registered with ELB, it performs continuous Health check. Once if it finds the unhealthy instance ELB will stop sending the traffic.
ELB can either be public or private it is based on the subnet where we are launching it. It is highly recommended to use 2 AZ's for high availablity.
ELB creates instances in the subnet's in backend which we cannot see. Private IP's for ELB will be assigned from the subnet which we have selected for the ELB. ELB will expand based on the traffic. Traffic will be distributed to Availablity zone's in round robin manner.
ELB creates instances in the subnet's in backend which we cannot see. Private IP's for ELB will be assigned from the subnet which we have selected for the ELB. ELB will expand based on the traffic. Traffic will be distributed to Availablity zone's in round robin manner.
Note: ELB can be accessed only by DNS CNAME and not by IP.
Cross zone load balancing
It will be useful if we are using multiple zones and if the number of instances in the zones are not equal. For example, If we have 6 Instances in 2 AZ's and in Zone A 4 instance and Zone B 2 instance. ELB will blindly forward the requests in Round robin manner to Zone A & B which causes the instances in Zone B to handle more load compared to the instances in Zone A. To Over com this we can enable cross zone load balancing option.
It will be useful if we are using multiple zones and if the number of instances in the zones are not equal. For example, If we have 6 Instances in 2 AZ's and in Zone A 4 instance and Zone B 2 instance. ELB will blindly forward the requests in Round robin manner to Zone A & B which causes the instances in Zone B to handle more load compared to the instances in Zone A. To Over com this we can enable cross zone load balancing option.
If cross Load Balancing is enabled then ELB will take
the count of all the instances in all the availablity zone's and will forward the traffic to instance
which has least number of connections.
Pre - Warming
If you expect a sudden increase in your hits. For eg: from 1 to 10,000 hits in particular time then it will take some time for ELB to auto scale in backend. To avoid this get your ELB pre warmed by contacting AWS support. They will configure the load balancer to have the appropriate level of capacity based on the traffic that you expect.
They also need some more details like Start and End dates, Expected flash traffic, Expected request rate per second and the total size of the typical request/response.
Pre - Warming
If you expect a sudden increase in your hits. For eg: from 1 to 10,000 hits in particular time then it will take some time for ELB to auto scale in backend. To avoid this get your ELB pre warmed by contacting AWS support. They will configure the load balancer to have the appropriate level of capacity based on the traffic that you expect.
They also need some more details like Start and End dates, Expected flash traffic, Expected request rate per second and the total size of the typical request/response.
Connection Draining
If enabled, time you give to the instances to complete the already establieshed connection for the unhealthy instances. But it wont send any new traffic to those unhelathy instance.
If enabled, time you give to the instances to complete the already establieshed connection for the unhealthy instances. But it wont send any new traffic to those unhelathy instance.
Internal load balancer - Load balancer launched in the private network.
If an instance is using ELB that doesnt mean the EC2 can download files from internet.
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