Using Elastic Load Balancing and Auto Scaling via AWS SDK for Java

Elastic Load Balancer acts as a network router that sends incoming requests to multiple EC2 instances sitting behind it in a round-robin fashion. The instances it points to can be added dynamically with an Auto Scaling Group. Amazon's Auto Scaling service automatically adds or removes computing resources allocated to an application, by responding to changes in demand.

Interact with the Elastic Load Balancer via AWS SDK. 

The “listeners” object redirects HTTP:80 requests from the load balancer to HTTP:80 on the instance.

ELB Health Check page could be established via the HealthCheck class and the ConfigureHealthCheckRequest class. Details could be found at "AWS SDK for Java API Reference" at (http://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/)

AutoScaling is commonly used together with CloudWatch which invokes the appropriate scaling policies.
Prior to launching AutoScaling Groups, specify Launch Configuration using the CreateLaunchConfigurationRequest class and the createLaunchConfiguration() method.
Similarly, launch AutoScaling Group using the CreateAutScalingGroupRequest class and createAutoScalingGroup() method.
Utilize the PutScalingPolicyRequest class to specify scaling in/out policies, after setup the policy by putScalngPolicy() method, record down the policy Amazon Resource Number (ARN) by calling getPolicyARN() method.

Create a CloudWatch Alarm could be a little different. First specify the alarm dimension with value as name of launched ASG. 

addARN variable refers to the ARN of the scaling out policy while snsARN refers to ARN of certain SNS action (such as sending emails). Thereafter, create object of PutMetricAlarmRequest class, specify Namespace as “AWS/EC2”, Dimensions&AlarmActions as the ones defined above. Other metrics such as Statistics/Period/Threshold… depend on different scenarios.

Finally, please notice that EC2, ELB, ASG, etc all use different Tag class.